NADPNADPHsystemene

NADP+/NADPH is a pair of coenzymes used as key electron carriers in cellular metabolism. Unlike NAD+/NADH, which primarily support energy production, the NADP+/NADPH system provides reducing power for biosynthetic processes and for maintaining cellular redox balance. NADPH is the reduced form; NADP+ is the oxidized form. The interconversion between these forms is driven by various dehydrogenases and reductases in different cellular compartments.

In photosynthetic organisms, NADP+ accepts electrons during the light-dependent reactions of photosynthesis to form NADPH. The produced NADPH is then used in the Calvin cycle to drive carbon fixation, transforming carbon dioxide into sugars. Ferredoxin-NADP+ reductase catalyzes the final reduction to NADPH, linking light energy to biosynthetic needs.

In non-photosynthetic cells, NADPH mainly arises from the pentose phosphate pathway, malic enzyme, isocitrate dehydrogenase, and other reductive processes. NADPH supplies reducing equivalents for fatty acid and cholesterol synthesis, nucleotide synthesis, and the maintenance of redox homeostasis through systems like glutathione reductase and thioredoxin reductase. It also serves as a substrate for NADPH oxidases in immune cells to generate reactive oxygen species for microbial killing.

Clinical and physiological relevance includes the dependence of redox-sensitive processes on adequate NADPH levels. Defects in NADPH production, such as glucose-6-phosphate dehydrogenase deficiency, can lead to oxidative stress. Cancer cells and other rapidly proliferating tissues often exhibit rewired NADPH metabolism to support growth and detoxification.