Biochemistry and Molecular Biology - Belyasova N.A. 2002

Metabolism. Processes leading to energy storage
Respiration
Redox potential of components

The Components of the Respiratory Chain behave as typical redox systems, alternating between reduced and oxidized states during electron transport. Their arrangement within the membrane is determined by their redox potential (RP), which serves as a measure of the tendency of compounds or elements to donate electrons.

Much like chemical elements, cellular metabolites can also be arranged in a series according to their redox potential (E0) at a 1/2 reduction level. A negative redox potential indicates that a given substance has a lower electron affinity than molecular hydrogen. Conversely, positive values of E0 characterize a higher electron affinity compared to H2. Thus, a strong reducing agent, such as NADH, has a negative E0, whereas a strong oxidizing agent (such as O2) has a positive E0. In biochemistry, it is customary to use the standard redox potential E0' adjusted to pH 7. The E0' values of individual respiratory chain components range from (-) 0.32 V (for NAD+/NADH) to (+) 0.82 V (for O2-/1/2. Thus, pyridine nucleotide-linked carriers initiate the respiratory chain, i.e., are located at its beginning, while molecular oxygen completes the chain by acting as the terminal electron acceptor.

The difference in redox potentials between two reacting substances serves as a measure of the Gibbs Free energy change in a chemical reaction, representing the useful work the system can perform. Comparing the redox potentials of the respiratory chain components reveals three oxidation steps that release sufficient energy to synthesize an ATP molecule (at least -0.15 V). Table 12.1 presents the E0' values of the main respiratory chain components, as well as the potential differences (∆E0) of the interacting systems.

Class="center">Table 12.1. Redox potentials of the components of the respiratory chain

Component

E0', V

∆E0, V

ATP synthesis

NAD+/NADH

-0.32

-0.02

no

FMN/FMNH2

-0.30

-0.05

no

FeS/FeS(2e)

-0.25

-0.27

yes

Q/QH2

+0.02

-0 01

no

Cytochrome b (Fe3+/Fe2+)

+0.03

-0.19

yes

Cytochrome c1 (Fe3+/Fe2+)

+0.22

-0.02

no

Cytochrome c (Fe3+/Fe2+)

+0.24

-0.01

no

Cytochrome a*a3 (Fe3+/Fe2+)

+0.25*, +0.39

-0.43

yes

O2-/1/2O2

+0.82



Last update: 06/08/2026

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