Bioenergetics and high-energy compounds Tomáš Kučera tomas.kucera@lfmotol.cuni.cz Department of Medical Chemistry and Clinical Biochemistry 2nd Faculty of Medicine, Charles University in Prague and Motol University Hospital 2017
Bioenergetics how organisms gain, convert, store and utilize energy
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
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)
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
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 139.7 acetate 369.2 acetyl-coa 374.1 a cis-aconitate 3 920.9 C 2 (g) 394.4 C 2 (aq) 386.2 HC 3 587.1 citrate 3 1166.6 dihydroxyacetone 2 1293.2 ethanol 181.5 fructose 915.4 fructose-6-phosphate 2 1758.3 fructose-1,6-bisphosphate 4 2600.8 fumarate 2 604.2 α-d-glucose 917.2 glucose-6-phosphate 2 1760.3 Compound G 0 f (kj mol 1 ) glyceraldehyde-3-phosphate 2 1285.6 H + 0.0 H 2 (g) 0.0 H 2 (l) 237.2 isocitrate 3 1160.0 α-ketoglutarate 2 798.0 lactate 516.6 l-malate 2 845.1 H 157.3 oxaloacetate 2 797.2 phosphoenolpyruvate 3 1269.5 2-phosphoglycerate 3 1285.6 3-phosphoglycerate 3 1515.7 pyruvate 474.5 succinate 2 690.2 succinyl-coa 686.7 a a for formation from free elements + free CoA Rewritten after Voet, D., Voet, J. G.: Biochemistry, John Wiley & Sons, Inc., 2011 (4th edition)
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
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
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 ]
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 H22 2 +0,29 + 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)
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
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)
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 0.8 0.95) [ATP] + 1 2 [ADP] [ATP] + [ADP] + [AMP] adenylate kinase: ATP + AMP 2 ADP ATP is formed using more exergonic reactions
Coupled reactions A B G 0 = 16.7 kj mol 1 [B] [A] = K eq = e G RT 0 = 1.15 10 3 A + ATP + H 2 B + ADP + P + H + at equilibrium: K eq = [B] [A] [ADP][ P ] = 2.67 10 2 [ATP] G 0 = 13.8 kj mol 1 [B] [A] = K [ATP] eq [ADP][ P ] = 2.67 102 500 = 1.34 10 5 the equilibrium B/A ratio is 10 8 times higher! n ATP molecules hydrolyzed the ratio is 10 8n times higher!
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
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
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
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
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
The End konec the end Thank you for your attention!
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.
Free energy changes Compound G 0 f (kj mol 1 ) acetaldehyde 139.7 acetate 369.2 acetyl-coa 374.1 a cis-aconitate 3 920.9 C 2 (g) 394.4 C 2 (aq) 386.2 HC 3 587.1 citrate 3 1166.6 dihydroxyacetone 2 1293.2 ethanol 181.5 fructose 915.4 fructose-6-phosphate 2 1758.3 fructose-1,6-bisphosphate 4 2600.8 fumarate 2 604.2 α-d-glucose 917.2 glucose-6-phosphate 2 1760.3 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
Compound G 0 f (kj mol 1 ) glyceraldehyde-3-phosphate 2 1285.6 H + 0.0 H 2 (g) 0.0 H 2 (l) 237.2 isocitrate 3 1160.0 α-ketoglutarate 2 798.0 lactate 516.6 l-malate 2 845.1 H 157.3 oxaloacetate 2 797.2 phosphoenolpyruvate 3 1269.5 2-phosphoglycerate 3 1285.6 3-phosphoglycerate 3 1515.7 pyruvate 474.5 succinate 2 690.2 succinyl-coa 686.7 a a for formation from free elements + free CoA.: Biochemistry, John Wiley & Sons, Inc., 2011 (4th edition)
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
High-energy bonds electrostatic repulsion P H P H H P H + P other anhydrides phosphosulphates, acylphosphates carbamoylphosphate phosphoguanidines (phosphagens) phos phosphoarginine
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)
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 2 2 2 +0,29 + values H 2 ½ 2 +0,82 (oxidant) lower exergonic reaction endergonic reaction
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