NADPHNADP

NADPH and NADP (nicotinamide adenine dinucleotide phosphate) are a pair of related coenzymes that function as electron carriers in cellular metabolism. They exist in two interconvertible forms: the oxidized NADP+ and the reduced NADPH. A key structural difference from the NADH/NAD+ pair is an additional phosphate group at the 2' position of the ribose attached to the adenine moiety, which influences enzyme specificity and localization.

NADPH is primarily a reducing agent, donating electrons in biosynthetic (anabolic) reactions and in maintaining redox balance. It provides reducing equivalents for fatty acid and cholesterol synthesis, nucleotide synthesis, and the detoxification of reactive oxygen species and xenobiotics via glutathione reductase and thioredoxin systems. NADPH is also used by cytochrome P450 monooxygenases and by NADPH oxidases in immune cells, where it fuels the respiratory burst to generate microbicidal species.

NADPH is produced mainly by the oxidative branch of the pentose phosphate pathway (glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase). Additional sources include cytosolic isocitrate dehydrogenase (IDH1) and malic enzyme (ME1) as well as mitochondrial isoforms (IDH2, ME2), depending on cellular compartment.

The production and consumption of NADPH are tightly regulated and compartmentalized between the cytosol and mitochondria, reflecting tissue-specific needs. Clinically, deficiencies in NADPH production, such as glucose-6-phosphate dehydrogenase deficiency, can compromise redox defense. The NADPH/NADP+ ratio is commonly used as a metric of cellular redox state in research contexts.