NAD

All Sources -
Updated Media sources (1) About encyclopedia.com content Print Topic Share Topic
views updated

NAD (nicotinamide adenine dinucleotide) A coenzyme, derived from the B vitamin nicotinic acid, that participates in many biological dehydrogenation reactions (see formula). NAD is characteristically loosely bound to the enzymes concerned. It normally carries a positive charge and can accept one hydrogen atom and two electrons to become the reduced form, NADH. NADH is generated during the oxidation of food, especially by the reactions of the Krebs cycle. It then gives up its two electrons (and single proton) to the electron transport chain, thereby reverting to NAD+ and generating three molecules of ATP per molecule of NADH.

NADP (nicotinamide adenine dinucleotide phosphate) differs from NAD only in possessing an additional phosphate group. It functions in the same way as NAD although anabolic reactions (see anabolism) generally use NADPH (reduced NADP) as a hydrogen donor rather than NADH. Enzymes tend to be specific for either NAD or NADP as coenzyme.

views updated

NAD n. nicotinamide adenine dinucleotide: a coenzyme that acts as a hydrogen acceptor in oxidation-reduction reactions, particularly in the electron transport chain in cellular respiration. NAD and the closely related coenzyme NADP (nicotinamide adenine dinucleotide phosphate) are derived from nicotinic acid; they are reduced to NADH and NADPH, respectively.

views updated

NAD, NADP Nicotinamide adenine dinucleotide and its phosphate, the coenzymes derived from niacin. Involved as hydrogen acceptors in a wide variety of oxidation and reduction reactions.

views updated

NAD (USA) National Academy of Design
• Biochem. nicotinamide adenine dinucleotide
• Med. no abnormality detected
• (or n.a.d.) no appreciable difference
• not on active duty

views updated
views updated
views updated

NAD: see coenzyme.