Human Biochemistry, Volume 1 - Murray R. 1993

Bioenergetics and Carbohydrate and Lipid Metabolism
Biological Oxidation
Redox Equilibrium, Redox Potential

The change in Free energy associated with oxidation-reduction reactions is proportional to the tendency of the reactants to donate or accept electrons. Consequently, the free energy change of a redox process can be expressed not only by the value of ∆G°' (see Chapter 11), but also by the Redox Potential of the system (E0). Typically, the redox potential of a system (E0) is compared with the potential of a standard hydrogen electrode, which is set at 0.0 V at pH 0. However, for biological systems, it is more convenient to use the redox potential at pH 7.0 (E'0); at this pH, the potential of the hydrogen electrode is -0.42 V. The redox potentials of several systems of particular interest in mammalian physiology are listed in Table 12.1. By using this table, one can predict the direction of electron flow when one redox system is coupled with another.

Class="center">Table 12.1. Standard potentials of selected mammalian oxidation-reduction systems

System

E0', volts

Oxygen/Water

+0.82

Cytochrome $a_3$: Fe3+/Fe2+

+0,29

Cytochrome c: Fe3+/Fe2+

+0.22

Ubiquinone: oxid./red.

+0.10

Cytochrome b: Fe3+/Fe2+

+0.08

Fumarate/succinate

+0.03

Flavoprotein ("yellow enzyme"): oxid./red.

-0.12

Oxaloacetate/malate

-0.17

Pyruvate/lactate

-0.19

Acetoacetate/β-hydroxybutyrate

-0.27

Lipoate: oxid./red.

-0.29

NAD+/NADH

-0.32

H+/H2

-0.42

Succinate/α-ketoglutarate

-0.67


Last update: 06/08/2026

Editorial and Educational Adaptation: This material has been compiled based on the primary/original source text. The project team performed an editorial review, corrected technical inaccuracies, structured sections, and adapted the content for an educational format.

What was processed:

  • elimination of formatting defects (OCR errors, structural breaks, corrupted characters);
  • editorial organization of content;
  • standardization of terminology in accordance with academic sources;
  • verification of factual statements against the original source text.

All mentions of the author, publication year, and origin of the primary text have been preserved in accordance with the source.