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1 Supplementary Materials for Conversion of alcohols to enantiopure amines through dual-enzyme hydrogenborrowing cascades Francesco G. Mutti,* Tanja Knaus, Nigel S. Scrutton, Michael Breuer, Nicholas J. Turner* *Corresponding author. (N.J.T.); (F.G.M.) Published 25 September 2015, Science 349, 1525 (2015) DOI: /science.aac9283 This PDF file includes: Materials and Methods Figs. S1 to S12 Tables S1 to S20

2 List of Abbreviations ADH: alcohol dehydrogenase LBv-ADH: ADH variant NAD + -dependent originated from the ADH from Lactobacillus brevis AA-ADH: ADH originated from Aromatoleum aromaticum ht-adh: ADH originated from Bacillus stearothermophilus AmDH: amine dehydrogenase (variant) Ph-AmDH: amine dehydrogenase variant originated from the phenylalanine dehydrogenase from Bacillus badius. Ch1-AmDH: chimeric amine dehydrogenase generating through domain shuffling of Ph-AmDH variant and L-AmDH variant, the latter originated from the leucine dehydrogenase from Bacillus stearothermophilus GDH: glucose dehydrogenase from Bacillus subtilis 1

3 List of substrates List 1 O O OH F OH OH OH 1a 1b 1c 1d OH OH OH 1e 1f 1g OH OH OH O OH 1h OH 1i OH 1j F OH F F 1k 1l 1m 1n List 2 OH OH 1o 1p OH OH OH 1q 1r 1s 2

4 List 3 1t OH 1u OH 1v OH 1w OH 1x OH 1y OH 1z OH Materials and Methods Chemicals Racemic secondary alcohols 1a,g,i,l-s, enantiopure secondary alcohol (R)-1a,i,l,g, enantiopure secondary alcohols (S)-1a,i,l,o-r, primary alcohols 1t-z, ketones 2a,b,f-l, aldehydes 2t-y, enantiopure (R), (S) or racemic amines 3g,i,l,r,s and non-chiral amines 3t-z were purchased from Sigma-Aldrich (Steinheim, Germany). Ketones 2c,d,e,m,n were purchased from Alfa Aesar (Shore Road, Heysham, UK). Aldehyde 2z was purchased from Acros Organics (Geel, Belgium). Nicotinamide cofactors (NADH and NAD + ) were purchased from Melford Biolaboratories (Chelsworth, Ipswich, UK). Racemic secondary alcohols 1b-f,h, were chemically synthesised by reduction with LiAlH 4 from the related ketones. Enantiopure secondary alcohols (S)-1b-h,j,k,m,n and (R) 1b-f,h,j,k,m-s were synthesised by enzymatic reduction of the related ketones with stereocomplementary ADHs according to procedures reported in literature (33). Enantiopure (S) and (R) amines 3a-f,h,j,k,m-q were synthesised by stereoselective amination using established enzymatic methods (commercially available stereocomplementary ω-transaminases) (34). Enzymes The stereocomplementary NAD-dependent ADHs (AA-ADH and LBv-ADH) were prepared as described before (22,24). The primary ht-adh and the Ph-AmDH were expressed as recombinant enzyme in E. coli BL21(DE3) cells. Synthetic genes encoding for ht-adh and Ph-AmDH were purchased from GeneArt -Life Technologies (ZMarketPlace, UK). Lysozyme from chicken egg white (3.2 mg, Sigma L6876, lyophilised powder, protein 95%, >40000 U/mg protein) was purchased from Sigma- Aldrich (Steinheim, Germany). E. coli BL21(DE3) cells and Thrombin Cleavage Capture Kit were purchased from Novagen (San Diego, CA, USA). Ni 2+ affinity columns (HisTrap FF, 5 ml) were purchased from GE Healthcare Bio- Sciences (Munich, Germany). 5

5 Analytics The conversions for the hydrogen-borrowing amination of the alcohols were measured by GC using an Agilent 7890 A GC system, equipped with an FID detector and using an Agilent J&W DB-1701 column (60 m, 250 μm, 0.25 μm) or an Agilent J&W DB-1701 column (30 m, 250 μm, 0.25 μm). Helium was used as carrier gas and CH 2 Cl 2 or EtOAc was used as solvent. The ees of amines were measured by GC using an Agilent 7890 A GC system, equipped with a FID detector and using a Varian Chrompack Chiracel Dex-CB column (25 m, 320 μm, 0.25 μm) Enzymes expression and purification a) His-tagged Ph-AmDH The Ph-AmDH variant was expressed in E. coli BL21 (DE3) according to the standard protocol from the supplier. Colonies were cultivated on an agar plate LB/Kanamycin (50 mg L -1 ). A single colony of E. coli BL21/His-tagged Ph-AmDH was taken from the agar plate and it was inoculated in LB/Kan (50 mg L -1 ) and grown overnight at 37 C, 170 rpm, for 16 h. Then, 4 large cultures (4 800 ml) containing LB/Kan (50 mg L -1 ) were inoculated with the overnight culture (15 ml each). The OD 600 was checked after 2 h and it was found to be around 0.7. Then, cultures were induced with IPTG (final concentration 0.5 mm) and further shaken at 170 rpm, at 20 C, for 24 h. Cultures were harvested, centrifuged and the pellets were washed with an aqueous solution of NaCl (5% w w -1 ). Pellets were frozen and stored at -20 ºC. The total amount of wet cells was 15.2 g. Two Ni 2+ columns (5 ml 2) were washed with water (50 ml) and conditioned with lysis buffer (10 mm imidazole, ph 8, 50 mm KH 2 PO 4, 300 mm NaCl, 50 ml). The wet cells containing the Ph-AmDH variant (ca. 9.2 g) were suspended in the lysis buffer (40 ml, 10 mm imidazole buffer, ph 8, 50 mm KH 2 PO 4, 300 mm NaCl). The whole cells were initially disrupted with lysozyme (1 mg ml -1 ) by shaking at 150 rpm, at 20 C for minutes. The mixture was diluted with the lysis buffer up to 80 ml. Then, the disruption was completed by sonication (5 min, amplitude 45%, pulse on 20 s, pulse off 40 s). The suspension was centrifuged (20000 rpm, 1 h, 4 C) and the supernatant was filtrated first through a 0.45 µm filter and then through 0.20 µm filter. The solution was then loaded into the previously conditioned columns. The columns were washed with the washing buffer (imidazole 25 mm, ph 8, 50 mm KH 2 PO 4, NaCl 300 mm, 75 ml). The column was then eluted with the elution buffer (4 ml 10 fractions, imidazole 300 mm, ph 8, 50 mm KH 2 PO 4, NaCl 300 mm). Fractions were analyzed by SDS-gel page. SDS-gel page showed that Ph-AmDH was obtained with elevate purity (> 99%). The fractions containing the highly purified His-tagged Ph-AmDH were combined and dialyzed overnight against potassium phosphate buffer (8 L, ph 8, 50 mm). The enzyme solution was concentrated and the concentration was measured spectrophotometrically (ε = M -1 cm -1 at λ= 280 nm). 477 mg of protein were obtained from 9.2 g of wet cells, equal to 1.9 L of culture, without further optimization. 6

6 Fig. S1 SDS-gel page showing the fractions containing the purified His-tagged Ph- AmDH b) His-tagged Ch1-AmDH The chimeric Ch1-AmDH variant was expressed in E. coli BL21 (DE3) as previously described for the Ph-AmDH variant. The total amount of wet cells was ca. 5.5 g of cells per liter of culture. Purification of the His-tagged Ch1-AmDH was carried out as previously described for the Ph-AmDH. Fractions were analyzed by SDS-gel page. SDS-gel page showed that Ch1-AmDH was obtained with elevate purity (> 99%). The fractions containing the highly purified His-tagged Ch1-AmDH were combined and dialyzed overnight against potassium phosphate buffer (8 L, ph 8, 50 mm). The enzyme solution was concentrated and the concentration was measured spectrophotometrically ( ɛ = M -1 cm -1 at λ= 280 nm). The yield of purification was ca. 165 mg of pure enzyme per liter of culture, without further optimization. Fig. S2 SDS-gel page showing the fractions containing the purified His-tagged Ch1- AmDH c) AA-ADH and LBv-ADH Crude cell extracts of AA-ADH and LBv-ADH were prepared as described elsewhere (22,24). An aliquot of enzyme cell extract was thawed and centrifuged (18000 rpm, 40 min, 4 C). The lysate was used for the enzyme purification whereas cell debris was discharged. The lysate was first passed onto a HiPrep 26/10 Desalting column (GE 7

7 Healthcare, bed volume 53 ml), eluting with Tris-HCl buffer (20 mm, ph 8.0). The buffer was supplemented with MgCl 2 (1 mm) for the purification of LBv-ADH. The solutions AA-ADH and LBv-ADH were then purified by anion exchange chromatography using a HiPrepQ HP 16/10 column (GE Healthcare). The elution of the ADH was performed with a gradient between start buffer (Tris-HCl buffer 20 mm, ph 8.0) and elution buffer (20 mm Tris-HCl, 1M NaCl, ph 8.0). The buffer was supplemented with MgCl 2 (1 mm) for the purification of LBv-ADH. After SDS-gel page, fractions containing the desired ADH in a sufficient purity were pooled. In the second step, AA-ADH and LBv-ADH were additionally purified using size exclusion chromatography (Superdex /10, GE Healthcare) using a 50 mm Tris- HCl, 150 mm NaCl ph 8.0 buffer. The buffer was supplemented with MgCl 2 (1 mm) for the purification of LBv-ADH. The fractions containing the ADH in high purity were combined and dialyzed overnight in 50 mm Tris-HCl ph 8.0. The protein solutions were concentrated using Centripreps (Millipore) and the final protein concentration determined at 280 nm (ε 280 [M -1 cm -1 ]: LBv-ADH = 20000, AA- ADH = 22500). Fig. S3 SDS-gel page of purified alcohol dehydrogenases. A) Lane 1: Biorad Precision Plus Protein Unstained Standard, lane 2: AA-ADH; B) lane 3: Biorad Precision Plus Protein Unstained Standard, lane 4: LBv-ADH. d) ht-adh The plasmid harboring the gene for the ht-adh was cloned in E. coli BL21 (DE3) cells. Colonies were cultivated on an agar plate LB/Amp (100 mg L -1 ). A single colony of E. coli BL21/hT-ADH was taken from the agar plate and it was inoculated in LB/Amp (100 mg L -1 ) and grown overnight at 37 C, 170 rpm, for 16 h. Then, 4 large cultures (4 800 ml) containing LB/Amp (100 mg L -1 ) were inoculated with the overnight culture (15 ml each). After 3 hours the OD 600 reached the value of 0.5. The cultures were induced with IPTG (1 mm) and further shaken at 170 rpm, at 20 C, for 24 h. Cultures were harvested, centrifuged and the pellets were washed with an aqueous solution of NaCl (5% w w -1 ). Pellets were frozen and stored at -20 ºC. The wet cell pellets (16.8 g) were suspended in the start buffer (80 ml, Tris-HCl, 20 mm, ph 8.0) and disrupted by sonication (pulse on 20 s; pulse off 30 s; cycles 10). The 8

8 mixture was then centrifuged (20000 rpm, 45 min, 4 C). The lysate was used for the enzyme purification whereas cell debris was discharged. The lysate was first passed onto a HiPrep 26/10 Desalting column (GE Healthcare, bed volume 53 ml), eluting with Tris- HCl buffer (20 mm, ph 8.0). ht-adh was initially purified by anion exchange chromatography using a HiPrepQ HP 16/10 column (GE Healthcare). The crude enzyme solution was loaded onto the column and the elution was performed with a gradient between start buffer and elution buffer (20 mm Tris/HCl, 1M NaCl, ph 8.0), After SDS-gel page, fractions containing the enzyme in a sufficient purity were combined and used in the following step. In the second step, the solution of ht-adh was additionally purified using size exclusion chromatography (Superdex200 16/10, GE Healthcare) and using a 50 mm Tris, 150 mm NaCl ph 8.0 buffer. The fractions containing the ht-adh in high purity were combined and dialyzed overnight in Tris-HCl (50 mm, ph 8.0). The protein solutions were concentrated using Centripreps (Millipore) and the final protein concentration determined at 280 nm (ε 280 [M -1 cm -1 ]: ADH-HT = 33390). Fig. S4 SDS-gel pages of purified ht-adh. C) lane 5: Biorad Precision Plus Protein Unstained Standard, lane 6: ht-adh. Reductive amination of para-fluoro phenyl-2-propanone (2b) in various buffer systems and at varied ph The reductive amination of ketone 2b has been reported in literature (19). This reaction was conducted using ammonium chloride buffer ca. 200 mm and at ph 9.6. NADH was used as cofactor. Nevertheless, the conditions for the reductive amination (2 nd step of the hydrogenborrowing cascade) should match, as far as possible, the optimal conditions for the alcohol oxidation (1 st step of the hydrogen-borrowing cascade). Hence, the influence of the ph was systematically investigated for the conversion of para-fluoro phenyl-acetone 2b (20 mm) as test substrate. All buffers were prepared from a solution of ammonia in distilled water (124 mm) that has an initial ph of ca Then, various buffer systems were prepared at different ph values by taking an aliquot of the ammonia solution and adjusting the ph through the subsequent addition of aliquots of an acid. Depending on the acid employed, the following buffers were obtained and used in this study: 9

9 a) Ammonium chloride b) Ammonium sulphate c) Ammonium formate d) Ammonium acetate e) Ammonium phosphate f) Ammonium borate g) Ammonium citrate h) Ammonium oxalate The range of ph values investigated obviously differed dependently on the chemical nature of the acid employed. The following reaction was performed in the previously mentioned buffers at different ph: Ph-AmDH NH + 4 / NH 3 F 2b O NADH NAD + F 3b NH 2 Scheme 1. Reductive amination of 2b employing His-tagged Ph-AmDH and stoichiometric NADH in ammonium/ammonia buffers at varied ph. For every ph value in a given buffer, the reaction was performed as a triplicate. The samples were then independently worked-up and analyzed. Every single point of the determination (Figure S1) was therefore the average value obtained from three independent experiments. Each sample was prepared by addition of highly purified Histagged Ph-AmDH (40 U) into the ammonium buffer at a given ph (final volume 1 ml). The substrate 2b was used at 20 mm concentration (2.67 µl). The cofactor NADH was used in stoichiometric amount with an excess of 10% (1.1 eq, 22 mm) and it was predissolved in the ammonium/ammonia buffer. The NADH was not used in catalytic amount in order to avoid the addition of a second enzyme such as the glucose dehydrogenase (for cofactor regeneration) that may be not stable in all the buffers and ph investigated. Reactions were shaken at 30 C, in an orbital shaker at 150 rpm, for 38 h. Work-up was performed as follows: a solution of KOH (200 µl, 10 N) was added and the aqueous solution was extracted with EtOAc (2 times 500 µl). The samples were dried with MgSO 4 anhydrous and the conversion was measured by GC-FID as reported in the section Analytics. The results are reported in figure S4. Results are reported as relative conversion (ordinate) vs ph (abscissa). 10

10 Rel. Conversion [%] ph NH 3 -chloride buffer NH 3 -acetic buffer NH 3 -phosphoric buffer NH 3 -boric buffer NH 3 -citric buffer NH 3 -oxalic buffer NH 3 -formic buffer NH 3 -solphoric buffer Figure S5. Reductive amination of 2b using the His-tagged Ph-AmDH in different buffer systems and at different ph. Reaction conditions: buffer (1 ml), Ph-AmDH highly pure (40 U), substrate 1b (20 mm), NADH (22 mm). Figure S4 shows that the optimal ph for the reductive amination is ph and the optimal buffer is ammonium chloride. Reductive amination of para-fluoro phenyl-2-propanone (2b) at different ammonium/ammonia concentration The reductive amination of 2b was further investigated under the optimised reaction conditions (ammonium chloride buffer ph 8.7). In particular, the reductive amination was carried out at increasing concentration of ammonium/ammonia in the buffer while keeping the ph constant. Ammonium chloride buffers at ph 8.7 were prepared at the following concentrations: 1) 100 mm; 2) 200 mm; 3) 381 mm; 4) 566 mm; 5) 727 mm; 6) 893 mm; 7) 1293 mm; 8) 1695 mm. The reductive amination of 2b was carried out using stoichiometric amount of NADH with an excess of 10% as well as with catalytic amount of NADH in presence of GDH/glucose for cofactor regeneration. The experiments and the results for the reductive amination of 2b with catalytic amount of NADH in presence of GDH / glucose are described below: 11

11 Ph-AmDH NH 4 Cl / NH 3 F O NADH NAD + F NH 2 Glucose GDH Gluconolactone Scheme S2. Reductive amination of 2b using His-tagged Ph-AmDH and catalytic NADH in ammonium chloride buffer (ph 8.7) at varied concentration. GDH and glucose were used for cofactor regeneration. A stock solution of NADH (1 mm), GDH (150 U) and glucose (60 mm) was prepared in the ammonium chloride buffer at a given concentration of the ammonium species. A concentrated solution of highly purified His-tagged Ph-AmDH (20 U) was added into the ammonium buffer (final volume 500 µl). The substrate 2b (20 mm) was finally added. Reactions were shaken at 30 C, in an orbital shaker at 150 rpm, for 16 h. Work-up was performed as follows: a solution of KOH (100 µl, 10 N) was added and the aqueous solution was extracted with EtOAc (2 300 µl). The samples were dried with MgSO 4 anhydrous and the conversion was measured by GC-FID as reported in the section Analytics. The results are reported in table S1. 12

12 Table S1 Reductive amination of 2b using the His-tagged Ph-AmDH at varied concentration of ammonium chloride buffer (ph 8.7). Reaction conditions: buffer (500 µl), Ph-AmDH (20 U), substrate 1b (20 mm), NADH (1 mm), glucose (60 mm), GDH (150 U). Sample Ammonium / ammonia concentration [mm] Conversion [%] >99.9 The biocatalytic reductive amination of para-fluoro-phenylacetone (20 mm) led to quantitative conversion (>99.5) when ca. 700 mm of ammonia / ammonium was applied. The cofactor NADH was used in catalytic amount (1 mm) and recycled with GDH / glucose. The ee of the amine product was >99% (R) Time study for the reductive amination of para-fluoro phenyl-2-propanone (2b) applying the optimal reaction conditions. In the previous set of experiments, it was shown that the biocatalytic reductive amination of 2b (20 mm) afforded quantitative conversion within 16 h when a 35-fold excess of ammonia/ammonium species was applied in presence of catalytic NADH (1 mm) and GDH/glucose for cofactor regeneration. In this further experiment, the conversion of the substrate into the amine product was monitored during the time. The optimal reaction conditions were applied (ammonium chloride buffer at ph 8.7, T 30 C). Catalytic NADH (1 mm) was recycled with GDH and glucose as previously described. A stock solution of NADH (1 mm), GDH (150 U) and glucose (60 mm) was prepared in the ammonium chloride buffer (ph 8.7, 727 mm). Every sample was prepared by addition of a concentrated solution of His-tagged Ph-AmDH (20 U) into the ammonium buffer (final volume 500 µl). The substrate 2b (20 mm) was finally added. Reactions were shaken at 30 C, in an orbital shaker at 150 rpm. The samples were quenched at different times according to the time schedule reported in Figure S5 (abscissa). Work-up was performed as follows: a solution of KOH (100 µl, 10 N) was added to each sample and the aqueous solution was extracted with EtOAc (2 300 µl). The samples were dried with MgSO 4 anhydrous and the conversion was measured by GC-FID as reported in the section Analytics. The results are depicted in figure S5. 13

13 Fig. S6 Time study for the reductive amination of 2b using the His-tagged Ph-AmDH applying the optimised reaction conditions (ammonium chloride ph 8.7, 727 mm). Reaction conditions: buffer (500 µl), Ph-AmDH highly pure (20 U), substrate 1b (20 mm), NADH (1 mm), glucose (60 mm), GDH (150 U). Under these reaction conditions, quantitative conversion was achieved after 12 h. The ee of the amine product was >99% (R) Hydrogen-borrowing amination of (R)-phenyl 2-propanol ((R)-1a) employing crude extract of LBv-ADH and purified His-tagged Ph-AmDH The hydrogen-borrowing amination of (R)-phenyl 2-propanol (1a) was performed using a crude cell extract of LBv-ADH in combination with the purified His-tagged Ph- AmDH. An aliquot of LBv-ADH crude extract was defrosted and the suspension was centrifuged (5 min, rpm, 4 ºC). Cell debris was removed and the supernatant was used for the experiments. The purified His-tagged Ph-AmDH was prepared as previously described in paragraph S3.a. The hydrogen-borrowing amination of 1a was accomplished in the following buffer systems: a) NH 4 Cl / NH 3 buffer (ca. ph 8.7, 100 mm). b) (NH 4 ) 2 SO 4 / NH 3 (ca. ph 8.7, 100 mm) c) HCOONH 4 / NH 3 buffer (ph 7.5, 100 mm) d) HCOONH 4 / NH 3 buffer (ph 8.0, 100 mm) e) HCOONH 4 / NH 3 buffer buffer (ph 8.5, 100 mm) f) Phosphate buffer (ph 7, 50 mm) + (NH 4 ) 2 SO 4 (100 mm) g) Phosphate buffer (ph 7.5, 50 mm) + (NH 4 ) 2 SO 4 (100 mm) h) Phosphate buffer (ph 8.0, 50 mm) + (NH 4 ) 2 SO 4 (100 mm) i) Phosphate buffer (ph 8.5, 50 mm) + (NH 4 ) 2 SO 4 (100 mm) j) Tris buffer (ph 7, 50 mm) + (NH 4 ) 2 SO 4 (100 mm) k) Tris buffer (ph 7.5, 50 mm) + (NH 4 ) 2 SO 4 (100 mm) l) Tris buffer (ph 8.0, 50 mm) + (NH 4 ) 2 SO 4 (100 mm) 14

14 m) Tris buffer (ph 8.5, 50 mm) + (NH 4 ) 2 SO 4 (100 mm) n) TEA buffer (ph 7, 50 mm) + (NH 4 ) 2 SO 4 (100 mm) o) TEA buffer (ph 7.5, 50 mm) + (NH 4 ) 2 SO 4 (100 mm) p) TEA buffer (ph 8.0, 50 mm) + (NH 4 ) 2 SO 4 (100 mm) q) TEA buffer (ph 8.5, 50 mm) + (NH 4 ) 2 SO 4 (100 mm) A stock solution of NAD + was prepared for every buffer employed in this study. The concentration of NAD + in the final reaction mixture, after the addition of the concentrated enzyme solutions of ADH and AmDH, was 1 mm. Therefore, every sample was prepared by addition of a concentrated solution of the purified N-terminal His-tagged Ph-AmDH (20 U) and a solution of crude cell extract of LBv-ADH (50 µl) into the reaction buffer (final volume 500 µl). The substrate (R)-1a (20 mm) was finally added. Reactions were shaken at 30 C, in an orbital shaker at 150 rpm, for 16 h. Work-up was performed as follows: a solution of KOH (100 µl, 10 N) was added to each sample and the aqueous solution was extracted with EtOAc (2 300 µl). The samples were dried with MgSO 4 anhydrous and the conversion was measured by GC-FID as reported in the section Analytics. The Results are reported in table 2. Table S2 Hydrogen-borrowing amination of (R)-1a using a crude cell extract of LBv- ADH and the N-terminal His-tagged Ph-AmDH in various buffer containing ammonium species (100 mm). Reaction conditions: buffer (500 µl), LBv-ADH (crude extract, 50 µl), purified Ph-AmDH (20 U), substrate 1a (20 mm), NADH (1 mm). Sample Buffer Amine Alcohol Ketone [%] [%] [%] 1 a b c d e f g h i j k l m n o p q

15 Formation of the amine product 3a was observed for the first time. However, conversions were mediocre. Furthermore, accumulation of the ketone intermediate 2a was observed. However, in this hydrogen-borrowing cascade, the concentration of 2a cannot theoretically exceed the concentration of the cofactor NAD + (that was 5 mol% in this experiment). The origin of the accumulation of 2a must be attributed to the presence of, at least, one NAD-oxidase from the host organism (E. coli) used for the expression of the ADH, as previously observed by other groups (35). The NADH-oxidase can compete with the AmDH in the second step for the oxidation of the NADH, leading to accumulation of 2a (scheme S3). H 2 O 2 or H 2 O Ph 20 mm NAD + OH 1a NADHoxidase ADH NADH Ph NAD + 1 mm NADH O Ph NH 2 * AmDH H 2 O O 2 2a Scheme S3. Schematic representation of the mechanism for the hydrogen-borrowing amination using purified Ph-AmDH in combination with crude cell extract of LBv-ADH. The first cycle performs the formal alcohol amination through oxidation of the alcohol 1a to the ketone 2a followed by the reductive amination to afford the amine product 3a. The NAD cofactor is recycled internally. However, using solutions containing recombinant non-purified enzyme, other enzymes can be present as impurities. In particular, a NADHoxidase from E. coli is highly active to perform the oxidation of NADH to NAD + at the expense of molecular oxygen. This second side-cycle produces an imbalance of the hydrogen-borrowing cascade, leading to the accumulation of the ketone intermediate 2a. 3a NH 3 Hydrogen-borrowing amination of (R)-phenyl 2-propanol ((R)-1a) combining purified LBv-ADH with purified His-tagged Ph-AmDH The hydrogen-borrowing amination of (R)-phenyl 2-propanol (1a) was performed using the purified LBv-ADH in combination with the purified His-tagged Ph-AmDH. The alcohol dehydrogenase was purified as described in paragraph S3.c. The purified His-tagged Ph-AmDH was prepared as previously described in paragraph S3.a. The hydrogen-borrowing amination of (R)-1a was accomplished in the following buffer systems: 16

16 The following buffers were employed, all of them at ph : 1) NH 4 Cl / NH 3 buffer (ca. ph 8.7, 100 mm). 2) (NH 4 ) 2 SO 4 / NH 3 (ca. ph 8.7, 100 mm) 3) HCOONH 4 / NH 3 buffer buffer (ph 8.5, 100 mm) 4) Phosphate buffer (ph 8.5, 50 mm) + (NH 4 ) 2 SO 4 (100 mm) 5) Tris buffer (ph 8.5, 50 mm) + (NH 4 ) 2 SO 4 (100 mm) 6) TEA buffer (ph 8.5, 50 mm) + (NH 4 ) 2 SO 4 (100 mm) A stock solution of NAD + was prepared for every buffer employed in this study. The concentration of NAD + in the final reaction mixture, after the addition of the concentrated enzyme solutions of ADH and AmDH, was 1 mm. Therefore, every sample was prepared by addition of a concentrated solution of the purified His-tagged Ph-AmDH (20 U) and a solution of purified LBv-ADH (50 µl, 50 mg ml -1 ) into the reaction buffer (final volume 500 µl). The substrate (R)-1a (20 mm) was finally added. Reactions were shaken at 30 C, in an orbital shaker at 150 rpm, for 16 h. Work-up was performed as follows: a solution of KOH (100 µl, 10 N) was added to each sample and the aqueous solution was extracted with EtOAc (2 300 µl). The samples were dried with MgSO 4 anhydrous and the conversion was measured by GC-FID as reported in the section Analytics. The Results are reported in table 3. Table S3 Hydrogen-borrowing amination of (R)-1a using purified LBv-ADH and the His-tagged Ph-AmDH in various buffer containing ammonium species (100 mm). Reaction conditions: buffer (500 µl), LBv-ADH (50 µl, 50 mg ml -1 ), purified Ph- AmDH (20 U), substrate 1a (20 mm), NADH (1 mm). Sample Buffer Amine [%] Alcohol [%] Ketone [%] Table S3 shows that the use of highly purified enzymes (LBv-ADH and Ph-AmDH) avoided for the accumulation of the ketone intermediate as observed in the previous set of experiments (paragraph S7). We have therefore demonstrated that the accumulation of the ketone was due to the activity of, at least, another enzyme that was present as an impurity in the crude cell extract of LBv-ADH. This enzyme must have been a NADHoxidase from E. coli as it was previously observed in other studies by other groups (35). In fact, NADH-oxidase oxidises the reduce cofactor that is produced in the first step of the cascade; therefore, NADH is not accessible to the Ph-AmDH for the reductive amination step. In fact, table S3 shows that the concentration of the ketone intermediate 2a was always below the maximum theoretical value of 5%, considering that the NAD + cofactor was present in 5 mol% concentration. 17

17 The concentration of the amine product 3a was really low (< 1%). However, we noticed that the reaction mixture containing the two enzymes became cloudy after the first few minutes of the reaction and, later, enzymes precipitation occurred. The precipitation of the enzymes was independent from the buffer of choice. A similar issue was also observed previously during the experiment combining the crude cell extract of LBv-ADH with the purified His-tagged Ph-AmDH (paragraph S7). Interestingly, when the enzymes LBv-ADH and the His-tagged Ph-AmDH were incubated separately in the same ammonium buffer, the solution did not become turbid and precipitation did not occur. As a consequence, the enzyme precipitation in the reaction mixture must be due to a mutual interaction between the LBv-ADH and the Histagged Ph-AmDH under the reaction conditions (buffer ph with ammonium species 100 mm). The ADHs employed in this study possess additional divalent cations (e.g. Mg 2+ ) that are essential for their stability. Furthermore, we noticed that stability of LBv-ADH is significantly improved during purification if Mg 2+ is added into the buffer, indicating a reversible dissociation process of the cation from the enzyme (see SM 4). At this stage, we speculated that enzyme precipitation may have been generated by interaction of the divalent cations such as Mg 2+ from the ADH with the His-terminal tag of the Ph-AmDH. This might lead to aggregation (the solution becomes initially turbid) followed by precipitation of the inactivated enzymes. To check if this was the reason for the enzymes precipitation and the consequent low conversion into amine 3a during the cascade reaction, the His-tag of the Ph-AmDH was cleaved (see paragraph S10). Cleavage of the His-tag from the purified Ph-AmDH and Ch1-AmDH Cleavage of the His-tag from purified Ph-AmDH The cleavage of the His-tag was carried out using biotinylated thrombin (Novagen) and following the procedure from the supplier with a slight modification (36). A solution of His-tagged Ph-AmDH (126 mg of enzyme in 2.25 ml of potassium phosphate buffer ph 8, 50 mm) was added to the cleavage buffer (50 ml, 20 mm Tris- HCl ph 8.4, 150 mm NaCl, 2.5 mm CaCl 2 ). A solution of biotinylated thrombin was then added (5 U). Preliminary experiments showed that the cleavage of the His-tag proceeded quantitatively at 20 C within 2 h with a negligible loss of the activity of the Ph-AmDH into the cleavage buffer. The results for the cleavage of the His-tag are reported in Fig. S7. 18

18 L A B C D Fig. S7. SDS gel page for the cleavage of the His-tag of the Ph-AmDH using biotinylated thrombin. L: ladder; A: sample of His-tagged Ph-AmDH (before the cleavage of the Histag); B,C and D: three samples of Ph-AmDH (cleavage of the His-tag after 60 min, 90 min and 120 min). The difference of MW between sample A and the other samples (B,C and D) is due to the cleavage of the protein tag. The residual thrombin present in the solution was removed by addition of streptavidin agarose beads. The residual thrombin bound to the beads. The agarose beads were then removed by centrifugation and subsequent filtration. The final solution contained the Ph-AmDH and the free His-tag. The cleaved His-tag was removed through Ni 2+ affinity chromatography. The final solution of highly pure Ph-AmDH devoid of the His-tag was dialyzed overnight in phosphate buffer (ph 8, 50 mm), concentrated, frozen in liquid nitrogen and stored at -80 C. The enzyme concentration was measured spectrophotometrically (ε = M -1 cm -1 at λ= 280 nm). Cleavage of the His-tag from purified Ch1-AmDH A solution of His-tagged Ch1-AmDH (138 mg of enzyme in 1.53 ml of potassium phosphate buffer ph 8, 50 mm) was added to the cleavage buffer (50 ml, 20 mm Tris- HCl ph 8.4, 150 mm NaCl, 2.5 mm CaCl 2 ). A solution of biotinylated thrombin was then added (5 U). Preliminary experiments showed that the cleavage of the His-tag proceeded quantitatively at 20 C within 2 h with a negligible loss of the activity of the Ch1-AmDH into the cleavage buffer. The results for the cleavage of the His-tag are reported in Fig. S8. 19

19 A B Fig. S8. SDS gel page for the cleavage of the His-tag of the Ch1-AmDH using biotinylated thrombin. A: sample of His-tagged Ch1-AmDH (before the cleavage of the His-tag); B: cleavage of the His-tag after 120 min. The difference of MW between sample A and B is due to the cleavage of the protein tag. The residual thrombin present in the solution was removed by addition of streptavidin agarose beads. The residual thrombin bound to the beads. The agarose beads were then removed by centrifugation and subsequent filtration. The final solution contained the Ch1-AmDH and the free His-tag. The cleaved His-tag was removed through Ni 2+ affinity chromatography. The final solution of highly pure Ph-AmDH devoid of the His-tag was dialyzed overnight in phosphate buffer (ph 8, 50 mm), concentrated, frozen in liquid nitrogen and stored at -80 C. The enzyme concentration was measured spectrophotometrically (ε = M -1 cm -1 at λ= 280 nm). Hydrogen-borrowing amination of (S)-phenyl 2-propanol ((S)-1a) combining purified AA-ADH with purified Ph-AmDH devoid of His-tag in ammonium chloride buffer (ph 8.7) at varied concentration of ammonium/ammonia The hydrogen-borrowing amination of (S)-phenyl 2-propanol ((S)-1a) was performed using the purified AA-ADH in combination with the purified Ph-AmDH devoid of the His-tag. The alcohol dehydrogenase AA-ADH was purified as described in paragraph S3.c. The purified His-tagged Ph-AmDH was prepared as described in paragraph S3.a and its His-tag was cleaved as described in paragraph S10). This set of experiments was performed in ammonium chloride buffer (ph 8.7) as these are the optimal conditions for the second step of the cascade (i.e. reductive amination). The concentration of the ammonium buffer was varied from 100 mm up to 4680 mm in order to test the impact of the concentration of ammonium/ammonia on the conversion. A stock solution of NAD + was prepared for every buffer employed in this study. The concentration of NAD + in the final reaction mixture, after the addition of the concentrated enzyme solutions of AA-ADH and Ph-AmDH, was 1 mm. Therefore, every sample was prepared by addition of a concentrated solution of the purified Ph-AmDH devoid of His- 20

20 tag (20 U) and a solution of the purified AA-ADH (20 µl, 47 mg ml -1 ) into the reaction buffer (final volume 500 µl). The substrate (S)-1a (20 mm) was finally added. Reactions were shaken at 30 C, in an orbital shaker at 150 rpm, for 24 h. Work-up was performed as follows: a solution of KOH (100 µl, 10 N) was added to each sample and the aqueous solution was extracted with CH 2 Cl 2 or EtOAc (2 300 µl). The samples were dried with MgSO 4 anhydrous and the conversion was measured by GC-FID as reported in the section Analytics. Table S4. Hydrogen-borrowing amination of (S)-1a using purified AA-ADH and Ph- AmDH devoid of the His-tag in ammonium chloride buffer (ph 8.7) at varied concentration. Reaction conditions: buffer (500 µl), AA-ADH (20 µl, 47 mg ml -1 ), purified Ph-AmDH (20 U), substrate (S)-1a (20 mm), NAD + (1 mm). Reaction time: 24 h. Ammonium/Ammonia concentration [mm] Amine [%] Alcohol [%] Ketone [%] The hydrogen-borrowing amination of (S)-1a proceeded indeed as expected, affording the amine product (R)-3a in all the cases investigated. The conversion gradually increased using increasing concentration of ammonium chloride buffer. However, concentrations above 2 M of ammonium/ammonia species seemed to be detrimental for the stability of, at least, one of the enzymes and/or NAD cofactor. In particular, ammonium/ammonia concentration above 4 M significantly worsened the conversion after 24 h. The amine product (R)-3a was obtained in perfect optically pure form. Time study for the hydrogen-borrowing amination of (S)-phenyl 2-propanol ((S)-1a) combining purified AA-ADH with purified Ph-AmDH devoid of His-tag in ammonium chloride buffer (ph 8.7, 2 M). The study was performed at varied concentration of NAD + cofactor. The hydrogen-borrowing amination of (S)-phenyl 2-propanol ((S)-1a) was performed using the purified AA-ADH in combination with the purified Ph-AmDH 21

21 devoid of the His-tag. The alcohol dehydrogenase AA-ADH was purified as described in paragraph S3.c. The purified His-tagged Ph-AmDH was prepared as described in paragraph S3.a and its His-tag was cleaved as described in paragraph S10. This set of experiments was performed in ammonium chloride buffer (ph 8.7, 2 M) as these were the optimal conditions from the study reported in paragraph S11. For a given set of experiments (fixed concentration of NAD + ), several samples were prepared in the same way and then quenched at different times according to the following schedule (1 h, 3 h, 6 h, 12 h, 18 h, 24 h, 48 h, 120 h). Every point was obtained as the average of three samples, quenched and worked-up at the same time. Stock solutions of NAD + were prepared in the ammonium chloride buffer (ph 8.7, 2 M). The concentrations of NAD + in the final reaction mixtures, after the addition of the concentrated enzyme solutions of AA-ADH and Ph-AmDH, were 1 mm or 0.5 mm or 0.2 mm or 0.1 mm. Each sample was prepared by addition of a concentrated solution of the purified Ph-AmDH devoid of His-tag (20 U) and a solution of the purified AA-ADH (20 µl, 47 mg ml -1 ) into the reaction buffer (final volume 500 µl). The substrate (S)-1a (20 mm) was finally added. Reactions were shaken at 30 C, in an orbital shaker at 150 rpm. The reactions were stopped according to the previously described time schedule. Work-up was performed as follows: a solution of KOH (100 µl, 10 N) was added to each sample and the aqueous solution was extracted with CH 2 Cl 2 or EtOAc (2 300 µl). The samples were dried with MgSO 4 anhydrous and the conversion was measured by GC-FID as reported in the section Analytics. The results are reported in table S5 and in Fig. 1 (main manuscript), and Fig. S7, S8, S9 Table S5. Time study for the hydrogen-borrowing amination of (S)-1a using purified AA-ADH and Ph-AmDH devoid of the His-tag in ammonium chloride buffer (ph 8.7, 2 M). The experiment was conducted with different concentrations of NAD + (1 mm, 0.5 mm, 0.2 mm and 0.1 mm). Reaction conditions: buffer (500 µl), AA-ADH (20 µl, 47 mg ml -1 ), purified Ph-AmDH (20 U), substrate (S)-1a (20 mm). Reaction time: 24 h. The amine product 3a was obtained in optically pure form (> 99% (R)). Time [h] NAD + [1 mm] NAD + [0.5 mm] NAD + [0.2 mm] NAD + [0.1 mm] Am Alc Ket Am Alc Ket Am Alc Ket Am Alc Ket End

22 Fig. 1. (as reported in the main manuscript). Asymmetric hydrogen-borrowing biocatalytic amination of (S)-1a (20 mm) to give (R)-3a using the AA-ADH and the Ph- AmDH with catalytic NAD + (1 mm, equal to 5 mol%). The reaction proceeds with inversion of configuration. Concentrations of the amine product (solid line), ketone intermediate (dotted line) and alcohol substrate (dashed line) were monitored during the time. As expected, the concentration of the ketone intermediate 2a remains constant during the time and below the concentration of the nicotinamide cofactor. Fig. S9. Asymmetric hydrogen-borrowing biocatalytic amination of (S)-1a (20 mm) to give (R)-3a using the AA-ADH and the Ph-AmDH with catalytic NAD + (0.2 mm, equal to 1 mol%). The reaction proceeds with inversion of configuration. Concentrations of the amine product (solid line), ketone intermediate (dotted line) and alcohol substrate (dashed line) were monitored during the time. As expected, the concentration of the ketone intermediate 2a remains constant during the time and below the concentration of the nicotinamide cofactor. 23

23 Fig. S10. Asymmetric hydrogen-borrowing biocatalytic amination of (S)-1a (20 mm) to give (R)-3a using the AA-ADH and the Ph-AmDH with catalytic NAD + (0.1 mm, equal to 0.5 mol%). The reaction proceeds with inversion of configuration. Concentrations of the amine product (solid line), ketone intermediate (dotted line) and alcohol substrate (dashed line) were monitored during the time. As expected, the concentration of the ketone intermediate 2a remains constant during the time and below the concentration of the nicotinamide cofactor. Time study for the hydrogen-borrowing amination of (S)-phenyl 2-propanol ((S)-1a) employing purified AA-ADH and purified Ph-AmDH devoid of the His-tag in ammonium chloride buffer (ph 8.7) and at different ammonium/ammonia concentration (2 M, 3 M, 4 M). The hydrogen-borrowing amination of (S)-phenyl 2-propanol ((S)-1a) was performed using the purified AA-ADH in combination with the purified Ph-AmDH devoid of the His-tag. The alcohol dehydrogenase AA-ADH was purified as described in paragraph S3.c. The purified His-tagged Ph-AmDH was prepared as described in paragraph S3.a and its His-tag was cleaved as described in paragraph S10. This set of experiments was performed in ammonium chloride buffer (ph 8.7) at different concentration of ammonium/ammonia (2 M, 3 M, 4 M). Several samples were prepared in the same way and then quenched at different times according to the following schedule (6 h, 12 h, 24 h, 48 h, 72 h). Every point was obtained as the average of three samples, quenched and worked-up at the same time. A stock solution of NAD + was prepared for every buffer employed in this study. The concentration of NAD + in the final reaction mixture, after the addition of the concentrated enzyme solutions of ADH and AmDH, was 1 mm. Therefore, every sample was prepared by addition of a concentrated solution of the purified Ph-AmDH devoid of the His-tag (20 U) and a solution of the purified AA-ADH (21 µl, 44.5 mg ml -1 ) into the reaction buffer (final volume 500 µl). The substrate (S)-1a (20 mm) was finally added. Reactions were shaken at 30 C, in an orbital shaker at 150 rpm. Work-up was performed as follows: a solution of KOH (100 µl, 10 N) was added to each sample and the aqueous solution was 24

24 extracted with CH 2 Cl 2 or EtOAc (2 300 µl). The samples were dried with MgSO 4 anhydrous and the conversion was measured by GC-FID as reported in the section Analytics. Results are reported in Table S6, S7 and S8. Table S6. Time study for the hydrogen-borrowing amination of (S)-1a using purified AA-ADH and Ph-AmDH devoid of the His-tag in ammonium chloride buffer (ph 8.7, 2 M). Reaction conditions: buffer (500 µl), AA-ADH (21 µl, 44.5 mg ml -1 ), purified Ph- AmDH (20 U), substrate (S)-1a (20 mm), NAD + (1 mm). The amine product 3a was obtained in optically pure form (> 99% (R)). Sample Time [h] Conversion [%] Amine Alcohol Ketone Table S7. Time study for the hydrogen-borrowing amination of (S)-1a using purified AA-ADH and Ph-AmDH devoid of the His-tag in ammonium chloride buffer (ph 8.7, 3 M). Reaction conditions: buffer (500 µl), AA-ADH (21 µl, 44.5 mg ml -1 ), purified Ph- AmDH (20 U), substrate (S)-1a (20 mm), NAD + (1 mm). The amine product 3a was obtained in optically pure form (> 99% (R)). Sample Time [h] Conversion [%] Amine Alcohol Ketone

25 Table S8. Time study for the hydrogen-borrowing amination of (S)-1a using purified AA-ADH and Ph-AmDH devoid of the His-tag in ammonium chloride buffer (ph 8.7, 4 M). Reaction conditions: buffer (500 µl), AA-ADH (21 µl, 44.5 mg ml -1 ), purified Ph- AmDH (20 U), substrate (S)-1a (20 mm), NAD + (1 mm). The amine product 3a was obtained in optically pure form (> 99% (R)). Sample Time [h] Conversion [%] Amine Alcohol Ketone Increasing the concentration of the ammonium chloride buffer from 2 M, to 3 M and finally 4 M, only slightly increased the conversion. The highest value for the conversion was 95% after 72 h and using 4 M of ammonium chloride buffer at ph 8.7. Hydrogen-borrowing amination of (R)-phenyl 2-propanol ((R)-1a) combining purified LBv-ADH with purified Ph-AmDH devoid of His-tag in ammonium chloride buffer (ph 8.7) at varied concentration of ammonium/ammonia The hydrogen-borrowing amination of (R)-phenyl 2-propanol ((R)-1a) was performed using the purified LBv-ADH in combination with the purified Ph-AmDH devoid of the His-tag. The alcohol dehydrogenase LBv-ADH was purified as described in paragraph S3.c. The purified His-tagged Ph-AmDH was prepared as described in paragraph S3.a and its His-tag was cleaved as described in paragraph S10. This set of experiments was performed in ammonium chloride buffer (ph 8.7) as these are the optimal conditions for the second step of the cascade (i.e. reductive amination). The concentration of the ammonium buffer was varied from 25 mm up to 4 M in order to test the impact of the concentration of the ammonium/ammonia on the conversion. A stock solution of NAD + was prepared for every buffer employed in this study. The concentration of NAD + in the final reaction mixture, after the addition of the concentrated enzyme solutions of LBv-ADH and Ph-AmDH, was 1 mm. Therefore, every sample was prepared by addition of a concentrated solution of the purified Ph-AmDH devoid of Histag (20 U) and a solution of the purified LBv-ADH (10 µl, 60 mg ml -1 ) into the reaction buffer (final volume 500 µl). The substrate (R)-1a (20 mm) was finally added. Reactions were shaken at 30 C, in an orbital shaker at 150 rpm, for 40 h. Work-up was performed as follows: a solution of KOH (100 µl, 10 N) was added to each sample and the aqueous solution was extracted with CH 2 Cl 2 or EtOAc (2 300 µl). The samples were dried with MgSO 4 anhydrous and the conversion was measured by GC-FID as reported in the section Analytics. The hydrogen-borrowing amination of (R)-1a did not proceed as expected. The highest conversion into the amine 3a was 3.62% using 200 mm of ammonium chloride buffer (ph 8.7). At this stage, we speculated that the reason might be a mediocre stability of the LBv-ADH in ammonium chloride buffer at ph 8.7. In fact, a white precipitate was 26

26 observed in all the samples prepared within 1 day reaction time. Hence, further experiments for the hydrogen-borrowing amination of (R)-1a combining LBv-ADH with Ph-AmDH will be conducted in other buffers (see paragraph S14). Table S9. Hydrogen-borrowing amination of (R)-1a using purified LBv-ADH and Ph-AmDH devoid of the His-tag in ammonium chloride buffer (ph 8.7) at varied concentration. Reaction conditions: buffer (500 µl), LBv-ADH (10 µl, 60 mg ml -1 ), purified Ph-AmDH (20 U), substrate (R)-1a (20 mm), NAD + (1 mm). Reaction time: 40 h. Ammonium/ammonia Concentration [mm] Amine [mm] Alcohol [mm] Ketone [mm] n. d n. d n. d Hydrogen-borrowing amination of (R)-phenyl 2-propanol ((R)-1a) combining purified LBv-ADH with purified Ph-AmDH devoid of His-tag in ammonium formate buffer (2 M) at varied ph The hydrogen-borrowing amination of (R)-phenyl 2-propanol ((R)-1a) was performed using the purified LBv-ADH in combination with the purified Ph-AmDH devoid of the His-tag. The alcohol dehydrogenase LBv-ADH was purified as described in paragraph S3.c. The purified N-terminal His-tagged Ph-AmDH was prepared as described in paragraph S3.a and its His-tag was cleaved as described in paragraph S10. This set of experiments was performed in ammonium formate buffer (2 M) at varied ph. Ammonium formate buffer was chosen as: i) the Ph-AmDH well-tolerates different buffers (i.e. ammonium chloride, formate, borate, citrate, acetate, oxalate, etc.); ii) the LBv-ADHs is a Mg 2+ dependent enzyme and, therefore, strong chelators such as oxalate, citrate and acetate must be avoided as buffer salts. Stock solutions of NAD + were prepared in the ammonium formate buffer (2 M) at ph 7, 7.5, 8 and 8.5. The buffers were additionally supplemented with MgCl 2 6H 2 0 (1 mm). The concentration of NAD + in the final reaction mixtures, after the addition of the concentrated enzyme solutions of LBv-ADH and Ph-AmDH, was 1 mm. Therefore, every sample was prepared by addition of a concentrated solution of the purified Ph- AmDH devoid of His-tag (20 U) and a solution of the purified LBv-ADH (25 µl, 38 mg ml -1 ) into the reaction buffer (final volume 500 µl). The substrate (R)-1a (20 mm) was finally added. Reactions were shaken at 30 C, in an orbital shaker at 150 rpm, for 24 h. 27

27 Work-up was performed as follows: a solution of KOH (100 µl, 10 N) was added to each sample and the aqueous solution was extracted with CH 2 Cl 2 or EtOAc (2 300 µl). The samples were dried with MgSO 4 anhydrous and the conversion was measured by GC-FID as reported in the section Analytics. Results are reported in table S10 Table S10. Hydrogen-borrowing amination of (R)-1a using purified LBv-ADH and Ph- AmDH devoid of the His-tag in ammonium buffer (2 M) at ph 7, 7.5, 8 and 8.5, supplemented with MgCl 2 6H 2 O (1 mm). Reaction conditions: buffer (500 µl), LBv- ADH (25 µl, 38 mg ml -1 ), purified Ph-AmDH (20 U), substrate (R)-1a (20 mm), NAD + (1 mm). Reaction time: 24 h. Sample ph Conversion [%] Amine Alcohol Ketone From Table S10, we can conclude that the LBv-ADH is much more stable in ammonium formate buffer rather than in ammonium chloride buffer since conversion of the alcohol (R)-1a into the amine (R)-3a was over 70%, although the reaction time was limited to 24 h. In particular, the optimum ph was 8.5. Therefore this ph value was used in the following experiments. Time study for the hydrogen-borrowing amination of (R)-phenyl 2-propanol ((R)- 1a) combining purified LBv-ADH with purified Ph-AmDH devoid of the His-tag in ammonium formate buffer (ph 8.5) and at different ammonium/ammonia concentration (2 M, 3 M, 4 M). The hydrogen-borrowing amination of (R)-phenyl 2-propanol ((R)-1a) was performed using the purified LBv-ADH in combination with the purified Ph-AmDH devoid of the His-tag. The alcohol dehydrogenase LBv-ADH was purified as described in paragraph S3.c. The purified His-tagged Ph-AmDH was prepared as described in paragraph S3.a and its His-tag was cleaved as described in paragraph S10. This set of experiments was performed in ammonium chloride formate (ph 8.5) at different concentration of ammonium/ammonia (2 M, 3 M, 4 M). Several samples were prepared in the same way and then quenched at different times according to the following schedule (6 h, 12 h, 24 h, 48 h, 72 h). Every point was obtained as the average of three samples, quenched and worked-up at the same time. A stock solution of NAD + was prepared for every buffer employed in this study. The concentration of NAD + in the final reaction mixture, after the addition of the concentrated enzyme solutions of LBv-ADH and Ph-AmDH, was 1 mm. Therefore, every sample was prepared by addition of a concentrated solution of the purified Ph-AmDH devoid of the His-tag (20 U) and a solution of the purified LBv-ADH (20 µl, 51.4 mg ml -1 ) into the 28