Table of standard reduction potentials for half-reactions important in biochemistry

The values below are standard reduction potentials for half-reactions measured at 25°C, 1 atmosphere and a pH of 7 in aqueous solution.[1][2]

The actual physiological potential depends on the ratio of the oxidized and reduced form according to the Nernst equation and the thermal voltage.


.

Where is the number of electrons involved in the reaction. For example, in a two electron couple like NAD+
:NADH the voltage becomes 30 mV more positive for every power of ten increase in the ratio of the oxidised to the reduced form.

Half-reaction Δξ°'(V) E' Physiological conditions References and notes
CH
3COOH + 2  H+ + 2  e− → CH
3CHO + H
2O		 −0.58 Many carboxylic acid: aldehyde redox reactions have a potential near this value
2 H+ + 2 e− → H
2		 −0.41
NADP+
 +  H+ + 2 e− → NADPH		 −0.320 −0.370 The ratio of NADP+
:NADPH is maintained at around 1:50.[3]
This allows NADPH to be used to reduce organic molecules
NAD+
 +  H+ + 2 e− → NADH		 −0.320 −0.280 The ratio of NAD+
:NADH is maintained at around 30:1.[3]
This allows NAD+
 to be used to oxidise organic molecules
FAD + 2 H+ + 2 e− → FADH
2
(coenzyme bonded to flavoproteins)		 −0.22 Depending on the protein involved, the potential of the flavine can vary widely[4]
Pyruvate + 2 H+ + 2 e− → Lactate -0.19 [5]
Oxaloacetate + 2 H+ + 2 e− → Malate -0.17 [6] While under standard conditions malate cannot reduce the more electronegative NAD+:NADH couple, in the cell the concentration of oxaloacetate is kept low enough that Malate dehydrogenase can reduce NAD+ to NADH during the citric acid cycle.
Fumarate + 2 H+ + 2 e− → Succinate +0.03 [5]
O
2 + 2 H+ + 2 e− → H
2O
2		 +0.30
O
2 + 4 H+ + 4 e− → 2H
2O		 +0.82
P680+
 +  e− → P680		 ~ +1.0

References
  1. Berg, JM; Tymoczko, JL; Stryer, L (2001). Biochemistry (5th ed.). WH Freeman. ISBN 9780716746843.
  2. Voet, Donald; Voet, Judith G.; Pratt, Charlotte W. (2016). "Table 14-4 Standard Reduction Potentials for Some Biochemically Import Half-Reactions". Fundamentals of Biochemistry: Life at the Molecular Level (5th ed.). Wiley. p. 466. ISBN 978-1-118-91840-1.
  3. Huang, Haiyan; Wang, Shuning; Moll, Johanna; Thauer, Rudolf K. (2012-07-15). "Electron Bifurcation Involved in the Energy Metabolism of the Acetogenic Bacterium Moorella thermoacetica Growing on Glucose or H2 plus CO2". Journal of Bacteriology. 194 (14): 3689–99. doi:10.1128/JB.00385-12. PMC 3393501. PMID 22582275.
  4. Buckel, W.; Thauer, R. K. (2013). "Energy conservation via electron bifurcating ferredoxin reduction and proton/Na+ translocating ferredoxin oxidation". Biochimica et Biophysica Acta (BBA) - Bioenergetics. 1827 (2): 94–113. doi:10.1016/j.bbabio.2012.07.002. PMID 22800682.
  5. Unden G, Bongaerts J (July 1997). "Alternative respiratory pathways of Escherichia coli: energetics and transcriptional regulation in response to electron acceptors". Biochimica Et Biophysica Acta. 1320 (3): 217–34. doi:10.1016/s0005-2728(97)00034-0. PMID 9230919.
  6. Huang, Li-Shar; Shen, John T.; Wang, Andy C.; Berry, Edward A. (2006). "Crystallographic studies of the binding of ligands to the dicarboxylate site of Complex II, and the identity of the ligand in the "oxaloacetate-inhibited" state". Biochimica et Biophysica Acta (BBA) - Bioenergetics. 1757 (9–10): 1073–1083. doi:10.1016/j.bbabio.2006.06.015. ISSN 0005-2728.


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