NADPHnyttjande

NADPHnyttjande describes how cells utilize NADPH as an electron donor in various biosynthetic and protective processes. NADPH differs from NADH in its primary role as a reducing equivalent for reductive biosynthesis and antioxidant systems rather than for ATP production. The main source of NADPH is the oxidative branch of the pentose phosphate pathway, catalyzed by glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase. Additional cytosolic sources include the malic enzyme and cytosolic isocitrate dehydrogenase; mitochondrial nicotinamide nucleotide transhydrogenase and related reactions also contribute.

Key uses include: fatty acid and cholesterol synthesis, where NADPH provides reducing power for elongation and biosynthetic steps; ribonucleotide reductase, which converts ribonucleotides to deoxyribonucleotides during DNA synthesis; and other anabolic processes such as nucleotide synthesis. Detoxification and antioxidant defense also rely on NADPH: glutathione reductase regenerates reduced glutathione; thioredoxin reductase maintains thioredoxin in its reduced form; cytochrome P450 and other monooxygenases use NADPH for xenobiotic metabolism; nitric oxide synthase uses NADPH as electron source for NO production. In phagocytes, the NADPH oxidase complex consumes NADPH to generate reactive oxygen species for microbial killing.

Regulation and distribution: most NADPH is in the cytosol, although mitochondria maintain their own NADPH pool via transhydrogenases and NADP+-dependent dehydrogenases. The NADPH/NADP+ ratio and the activity of PPP enzymes regulate flux. Clinically, G6PD deficiency reduces NADPH production in red blood cells, increasing susceptibility to oxidative damage. Cancer cells often show elevated NADPH demand to support growth and redox balance.