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Figure 16-8. Structure of FAD and its reduction to FADH2.

Figure 16-8Structure of FAD and its reduction to FADH2

The coenzyme flavin adenine dinucleotide (FAD) can accept one or two hydrogen atoms. The addition of one electron together with a proton (i.e., a hydrogen atom) generates a semiquinone intermediate. The semiquinone is a free radical because it contains an unpaired electron (denoted by a blue dot), which is delocalized by resonance to all the flavin ring atoms. The addition of a second electron and proton (i.e., a second hydrogen atom) generates the reduced form, FADH2. Flavin mononucleotide (FMN) is a related coenzyme that contains only the flavin – ribitol phosphate part of FAD (highlighted in blue).

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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