Bioenergetics and high-energy compounds

Transcription

1 Bioenergetics and high-energy compounds Tomáš Kučera Department of Medical Chemistry and Clinical Biochemistry 2nd Faculty of Medicine, Charles University in Prague and Motol University Hospital 2017

2 Bioenergetics how organisms gain, convert, store and utilize energy

3 Gibbs free energy G = H TS G = H T S = Q p T S G decrease in a biological process represents its maximum recoverable work. equilibrium: G = 0 spontaneous (exergonic) process: G < 0 (it can do work) endergonic process: G > 0

4 Gibbs free energy one of the thermodynamic potentials no information on the rate it is given by the mechanism (im-)possibility of a process given only by the initial and final states a catalyst (enzyme) can accelerate equilibrium attainment, not change its state possibility of coupling depends on temperature: equilibrium: T = H S H S G = H T S + Both enthalpically favored (exothermic) and entropically favored. Spontaneous (exergonic) at all temperatures. Enthalpically favored but entropically opposed. Spontaneous only at temperatures below T = H S. + + Enthalpically opposed (endothermic) but entropically favored. Spontaneous only at temperatures above T = H S. + Both enthalpically and entropically opposed. Unspontaneous (endergonic) at all temperatures. Rewritten from Voet, D., Voet, J. G.: Biochemistry, John Wiley & Sons, Inc., 2011 (4th edition)

5 Chemical equilibria Reaction a A + b B c C + d D G = G 0 + RT ln [C]c [D] d [A] a [B] b ( G 0 = standard G change of the reaction) constant term depends only on the reaction variable term depends on temperature and concentrations of reactants and products Equilibrium G = 0 [C] c [D] d K eq = [A] a [B] b G 0 = RT ln K eq = e G 0 RT G 0 and K eq directly related 10-fold change in K eq changes G 0 by 5.7 kj mol 1

6 Free energy changes G 0 = G 0 f (products) G 0 f (reactants) G 0 f = G 0 of formation Compound G 0 f (kj mol 1 ) acetaldehyde acetate acetyl-coa a cis-aconitate C 2 (g) C 2 (aq) HC citrate dihydroxyacetone ethanol fructose fructose-6-phosphate fructose-1,6-bisphosphate fumarate α-d-glucose glucose-6-phosphate Compound G 0 f (kj mol 1 ) glyceraldehyde-3-phosphate H H 2 (g) 0.0 H 2 (l) isocitrate α-ketoglutarate lactate l-malate H oxaloacetate phosphoenolpyruvate phosphoglycerate phosphoglycerate pyruvate succinate succinyl-coa a a for formation from free elements + free CoA Rewritten after Voet, D., Voet, J. G.: Biochemistry, John Wiley & Sons, Inc., 2011 (4th edition)

7 Free energy changes standard state activity 1 mol l 1 25 C 1 bar biochemical standard state water activity = 1 ph = 7 substances undergoing acid-base dissociation: c = total c of all species at ph = 7

8 Coupled reactions A + B C + D G 1 D + E F + G G 2 A + B + E C + F + G G 3 = G 1 + G 2 < 0 Glucose phosphorylation: Glc + ATP Glc-6- P + ADP endergonic reaction: glucose + P glucose-6- P G 0 = 13.8 kj mol 1 exergonic reaction: ATP + H 2 ADP + P G 0 = 30.5 kj mol 1 coupled reaction: glucose + ATP glucose-6- P + ADP G 0 = 16.7 kj mol 1

9 Redox potential also oxidation-reduction (reduction) potential expresses the substance s readiness to accept electrons ox + n e red (half-cell) Voet, D., Voet, J. G.: Biochemistry, John Wiley & Sons, Inc., 2011 (4th edition) A ox + B red n e A red + B ox ernst equation G = G 0 + RT ln [A red][b ox ] [A ox ][B red ] G = nf E E = E 0 RT nf ln [red] [ox] E = E 0 RT nf ln [A red][b ox ] [A ox ][B red ]

10 Redox potential E as an energy scale Reduced form xidized form E 0 (V) ΔG 0 acetaldehyde acetate -0,60 values higher H2 2H + -0,42 (reductant) isocitrate 2-oxoglutarate + C2-0,38 glutathione-sh glutathione-ss -0,34 ADH + H + AD + -0,32 glyceraldehyde-3-phosphate + H3P4 1,3-bisphosphoglycerate -0,28 FADH2 FAD -0,20 lactate pyruvate -0,19 malate oxalacetate -0,17 cytochrome b (Fe 2+ ) cytochrome b (Fe 3+ ) 0,00 succinate fumarate +0,03 dihydroubiquinone ubiquinone +0,10 cytochrome c (Fe 2+ ) cytochrome c (Fe 3+ ) +0,26 +ne ne H ,29 + values H2 ½ 2 +0,82 (oxidant) lower exergonic reaction endergonic reaction Voet, D., Voet, J. G.: Biochemistry, John Wiley & Sons, Inc., 2011 (4th edition) The actual direction of the reaction depends also on the [red]/[ox] ratio (and/or other factors)

11 Redox potential E 0 = 0 V for standard hydrogen half-reaction (electrode) H + at ph0, 25 C, 1 bar in equilibrium with Pt-black electrode saturated with H 2 ph = 7 E 0 = 0.421V

12 High-energy compounds contain high-energy bond hydrolyzed to drive endergonic reactions ATP a central role (universal energy currency of the cell) 3 phosphoryl groups bound by one phosphoester and two phosphoanhydride bonds H 2 P γ phosphoanhydride bonds P β phosphoester bond P α H H H H H H adenosine AMP ADP ATP Redrawn according to Voet, D., Voet, J. G.: Biochemistry, John Wiley & Sons, Inc., 2011 (4th edition)

13 ATP R 1 P + R 2 H R 1 H + R 2 P phosphoryl transfer reaction enormous metabolic significance ATP + H 2 ADP + P G 0 = 30.5 kj mol 1 ATP + H 2 AMP + P P G 0 = 45.6 kj mol 1 P P + H 2 2 P G 0 = 19.2 kj mol 1 kinetic stability, thermodynamic instability (high G 0 ) cell energy charge (usually ) [ATP] [ADP] [ATP] + [ADP] + [AMP] adenylate kinase: ATP + AMP 2 ADP ATP is formed using more exergonic reactions

14 Coupled reactions A B G 0 = 16.7 kj mol 1 [B] [A] = K eq = e G RT 0 = A + ATP + H 2 B + ADP + P + H + at equilibrium: K eq = [B] [A] [ADP][ P ] = [ATP] G 0 = 13.8 kj mol 1 [B] [A] = K [ATP] eq [ADP][ P ] = = the equilibrium B/A ratio is 10 8 times higher! n ATP molecules hydrolyzed the ratio is 10 8n times higher!

15 ATP consumption low-energy phosphorylated compounds TP interconversions formation of CTP, GTP, UTP, datp, dctp, dgtp, dttp nucleoside diphosphate kinase ATP + DP ADP + TP processes based on protein conformational changes protein folding active transport movements

16 ATP ATP formation substrate-level phosphorylation oxidative phosphorylation (photophosphorylation) adenylate kinase reaction phosphagens ATP turnover average adult resting person about 3 mol h 1 (1.5 kg h 1 ), i.e. about 40 kg d 1 strenuous activity up to 0.5 kg min 1

17 High-energy bonds no high-energy bond exists! phosphoanhydrides resonance stabilization higher solvation energy of the hydrolysis products electrostatic repulsion P H P H H P P H + P + R + P Redrawn from Berg, J. M., Tymoczko, Gatto, G. J. Jr., J. L., Stryer, L.: Biochemistry, W. H. Freeman and Company, 2012 (8th edition) other anhydrides phosphosulphates, acylphosphates carbamoylphosphate phosphoguanidines (phosphagens) phosphocreatine, phosphoarginine enol phosphates

18 High-energy compounds there are no high-energy compounds as well! H 2 P P P H H H H H H adenosine triphosphate (ATP) P P H H H H H H adenosine diphosphate (ADP) H 2 H 2C C P acetylphosphate (acylphosphates) phosphocreatine (phosphamides) H 2C P C C P phosphoenolpyruvate (enolphosphates) acetylcoenzyme A (thioesters) H C H + 2 CH 3 CH 2 CoA S CCH 3 C

19 Energy metabolism scheme amino acids fatty acids β-oxidation sugars glycolysis pyruvate alternative pathways ADH AD + ADH AD + fermentative AD + regeneration lactate ethanol propionate butyrate butanol formate H2 C2 acetate 2,3-butandiol succinate oxidative decarboxylation citric acid cycle Ac~S CoA Calvin cycle C 2 ADH AD + ADPH ADP + ADP respiratory chain 2 photosynthetic electron transport chain hν ADP ATP oxidative phosphorylation H 2 photophosphorylation ATP

20 The End konec the end Thank you for your attention!

21 Gibbs free energy depends on temperature: equilibrium: T = H S G = H T S + Both enthalpically favored (exothermic) and entropically favored. Spontaneous (exergonic) at all temperatures. Enthalpically favored but entropically opposed. Spontaneous only at temperatures below T = H S. + + Enthalpically opposed (endothermic) but entropically favored. Spontaneous only at temperatures above T = H S. + Both enthalpically and entropically opposed. Unspontaneous (endergonic) at all temperatures.

22 Free energy changes Compound G 0 f (kj mol 1 ) acetaldehyde acetate acetyl-coa a cis-aconitate C 2 (g) C 2 (aq) HC citrate dihydroxyacetone ethanol fructose fructose-6-phosphate fructose-1,6-bisphosphate fumarate α-d-glucose glucose-6-phosphate Com glyc H + H 2 H 2 isoc α-k lact l-m H oxa pho 2-ph 3-ph pyr suc suc a for f

23 Compound G 0 f (kj mol 1 ) glyceraldehyde-3-phosphate H H 2 (g) 0.0 H 2 (l) isocitrate α-ketoglutarate lactate l-malate H oxaloacetate phosphoenolpyruvate phosphoglycerate phosphoglycerate pyruvate succinate succinyl-coa a a for formation from free elements + free CoA.: Biochemistry, John Wiley & Sons, Inc., 2011 (4th edition)

24 High-energy compounds hydride bonds H 2 phosphoanhydride bonds phosphoester bond P γ P β P α H H H ADP ATP H H H adenosine AMP

25 High-energy bonds electrostatic repulsion P H P H H P H + P other anhydrides phosphosulphates, acylphosphates carbamoylphosphate phosphoguanidines (phosphagens) phos phosphoarginine

26 R P + + P edrawn from Berg, J. M., Tymoczko, Gatto,. J. Jr., J. L., Stryer, L.: Biochemistry, W. H. eeman and Company, 2012 (8th edition)

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28 Reduced form xidized form E 0 (V) ΔG 0 acetaldehyde acetate -0,60 values higher H 2 2H + -0,42 (reductant) isocitrate 2-oxoglutarate + C 2-0,38 glutathione-sh glutathione-ss -0,34 ADH + H + AD + -0,32 glyceraldehyde-3-phosphate + H 3P 4 1,3-bisphosphoglycerate -0,28 FADH 2 FAD -0,20 lactate pyruvate -0,19 malate oxalacetate -0,17 cytochrome b (Fe 2+ ) cytochrome b (Fe 3+ ) 0,00 succinate fumarate +0,03 dihydroubiquinone ubiquinone +0,10 cytochrome c (Fe 2+ ) cytochrome c (Fe 3+ ) +0,26 +ne ne H ,29 + values H 2 ½ 2 +0,82 (oxidant) lower exergonic reaction endergonic reaction

29 amino acids fatty acids β-oxidation sugars glycolysis pyruvate alternative pathways ADH AD + ADH AD + fermentative AD + regeneration lactate ethanol propionate butyrate butanol formate H2 C2 acetate 2,3-butandiol succinate oxidative decarboxylation citric acid cycle Ac~S CoA Calvin cycle C 2 ADH AD + ADPH ADP + ADP respiratory chain 2 photosynthetic electron transport chain hν ADP ATP oxidative phosphorylation H 2 photophosphorylation ATP