Nicotinamide adenine dinucleotide phosphate

Nicotinamide adenine dinucleotide phosphate, actually nicotinamide adenine dinucleotide phosphate, abbreviated NADP, is a hydride ion-transferring (H- = one proton/two electrons) coenzyme that is involved in numerous redox reactions of the cell's metabolism.

The abbreviations NADP+ for the oxidized form, NADPH for the reduced form and NADP in general are proposed by IUPAC/IUBMB.

The coenzyme was discovered by Otto Warburg in 1931 and was also known as triphosphopyridine nucleotide, abbreviated TPN, or as codehydrase II or codehydrogenase II or coenzyme II in older literature until the early 1960s.

NADPH is a derivative of NADH, namely the phosphorylated form (at the ribose moiety, C2') of the coenzyme NADH. There is a fundamental difference between NADH and NADPH in most biochemical reactions: NADH is derived from glycolysis and the citrate cycle in catabolism and oxidized in the respiratory chain to generate ATP. In contrast, NADPH acts as a reducing agent in anabolism, serving as a supplier of electrons and protons in reducing biosynthesis:

• during the synthesis of fatty acids NADPH is oxidized to NADP+ by fatty acid synthase.

• during the degradation of polyunsaturated fatty acids NADPH is oxidized to NADP+ (enzyme: 2,4-dienoyl-CoA-reductase).

• in the so-called polyol pathway, i.e. during the reduction of glucose to sorbitol, NADPH is oxidized to NADP+ by a reductase.

• during the reduction of fatty acids to the corresponding fatty alcohol, NADPH is oxidized to NADP+ by an acyl-CoA reductase.

• one source of NADPH is the direct oxidation of glucose-6-phosphate (G-6P) by glucose-6-phosphate dehydrogenase (G-6P-DH) in the pentose phosphate pathway. Measuring the amount of NADPH allows accurate determination of the amount of sugar converted in glucose-6-phosphate dehydrogenase, the NADPH molar amount is exactly proportional to the sugar molar amount. In the further course, the 6-phosphogluconate dehydrogenase generates another molecule of NADPH.

• NAD(P)H-dependent glutamate dehydrogenase reduces NAD to NADH in the course of amino acid degradation.

• in green plants NADPH is formed in the course of photosynthesis.

• In the citrate shuttle, NADPH is formed during the oxidative decarboxylation of oxaloacetate, which catalyzes an NADP-dependent malate enzyme.

The reduction capacity of NADPH can be transferred to glutathione.