Nicotinamide Coenzymes Are Used in Reactions Involving Hydride Transfers

Nicotinamide Coenzymes Are Used in Reactions Involving Hydride Transfers 

Nicotinamide adenine dinucleotide (NAD+) is one of the two coenzymatic forms of nicotinamide (fig. 10.6). The 

The nicotinamide coenzymes are biological carriers of reducing equivalents (electrons). The most common function of NAD+ is to accept two electrons and a proton (H equivalent) from a substrate undergoing metabolic oxida-tion to produce NADH, the reduced form of the coenzyme. This then diffuses or is transported to the terminal-electron transfer sites of the cell and reoxidized by terminal-electron acceptors, 02 in aerobic organisms, with the concomitant formation of ATP (chapter 14). Equations (8), (9), and (10) are typical reactions in which NAD+ acts as such an acceptor. 

Mechanisms of action of pyridoxal phosphate (a) in glutamate-oxaloacetate transaminase, and (b) in aspartate /3-decarboxylase. 

Structures of nicotinamide and nicotinamide coenzymes. The reactive sites of the coenzymes are shown in red. 

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Pyridoxal-5 -Phosphate Is Required for a Variety of Reactions with a-Amino Acids Nicotinamide Coenzymes Are Used in Reactions Involving Hydride Transfers Flavins Arq Used in Reactions Involving One or Two Electron Transfers... 

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