Figure 16-4. Structures of the electron-carrying coenzymes NAD+ and NADH.

Figure 16-4Structures of the electron-carrying coenzymes NAD+ and NADH

Nicotinamide adenine dinucleotide (NAD+) and the related nicotinamide adenine dinucleotide phosphate (NADP+) accept only pairs of electrons; reduction to NADH or NADPH involves the transfer of two electrons simultaneously. In most oxidation-reduction reactions in biological systems, a pair of hydrogen atoms (two protons and two electrons) are removed from a molecule. One of the protons and both electrons are transferred to NAD+; the other proton is released into solution. Thus the overall reaction is sometimes written NAD+ + 2 H+ + 2 e ↔ NADH + H+. NADP is identical in structure with NAD except for the presence of an additional phosphate group. However, NAD and NADP participate in different sets of enzymatically catalyzed reactions.

From: Section 16.1, Oxidation of Glucose and Fatty Acids to CO2

Cover of Molecular Cell Biology
Molecular Cell Biology. 4th edition.
Lodish H, Berk A, Zipursky SL, et al.
New York: W. H. Freeman; 2000.
Copyright © 2000, W. H. Freeman and Company.

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