Nicotinamide adenine dinucleotide

nicotinamide adenine dinucleotide and nicotinamide adenine dinucleotide phosphate: see coenzyme.

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Nicotinamide adenine dinucleotide (NAD)

An organic coenzyme and one of the most important components of the enzymatic systems concerned with biological oxidation-reduction reactions. It is also known as NAD, diphosphopyridine nucleotide (DPN) coenzyme I, and codehydrogenase I. NAD is found in the tissues of all living organisms. See Coenzyme

The nicotinamide, or pyridine, portion of NAD can be reduced chemically or enzymatically with the formation of reduced or hydrogenated NAD (NADH). NAD functions as the immediate oxidizing agent for the oxidation, or dehydrogenation, of various organic compounds in the presence of appropriate dehydrogenases, which are specific apoenzymes, or protein portions of the enzyme. In the dehydrogenase reactions one hydrogen atom is transferred from the substrate to NAD, while another is liberated as hydrogen ion.

NAD and its reduced form, NADH, serve to couple oxidative and reductive processes and are constantly regenerated during metabolism. Hence, they serve as catalysts and NAD is referred to as a coenzyme. In some enzymatic reactions a different coenzyme, triphosphopyridine nucleotide is required. Dehydrogenases are generally quite specific with respect to the coenzyme which they can utilize. See Enzyme, Nicotinamide adenine dinucleotide phosphate (NADP)