Biochemistry and Molecular Biology - Belyasova N.A. 2002

Metabolism. Processes Leading to Energy Storage
Respiration
Redox Potential of Components

Respiratory Chain components behave as typical redox systems, alternating between reduced and oxidized states during electron transport. The arrangement of these carriers within the membrane is determined by their redox potential (RP), which measures the ability of compounds or elements to donate electrons.

Much like chemical elements, substances functioning within Cells can also be arranged in a series according to their redox potential (E0) at a reduction state of 1/2. A negative redox potential indicates that the substance has a lower electron affinity than molecular hydrogen. Positive E0 values characterize a higher electron affinity than that of H2. Thus, a strong reducing agent, such as NADH, has a negative E0, while a strong oxidizing agent (e.g., O2) has a positive E0. In biochemistry, the E0' value adjusted to pH 7 is used. The E0' values of individual respiratory chain components range from (-) 0.32 V (for NAD+/NADH) to (+) 0.82 V (for O2-/1/2). Nicotinamide carriers begin the respiratory chain, i.e., they are located at its start, while molecular oxygen completes the chain, acting as the terminal electron acceptor.

The difference in redox potentials of two reacting substances can serve as a measure of the Free energy change in a chemical reaction, i.e., a measure of the useful work the system is capable of performing. Comparing the redox potentials of the respiratory chain components reveals three stages of oxidation where enough energy is released 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 difference (∆E0) of the interacting systems.

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



Last update: 06/08/2026

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