NAD+

Nicotinamide adenine dinucleotide (NAD+) is an essential coenzyme (MW 663.43 Da) found in all living cells, serving as a critical cofactor in over 500 enzymatic reactions. It exists in two interconvertible forms: the oxidized form (NAD+) and the reduced form (NADH). NAD+ is the central hub of cellular energy metabolism, transferring electrons from the citric acid cycle and glycolysis to the electron transport chain for ATP synthesis. Beyond bioenergetics, NAD+ functions as a substrate for three classes of regulatory enzymes — sirtuins (SIRT1-7), PARPs (poly-ADP-ribose polymerases), and CD38 — making it a fundamental regulator of DNA repair, gene expression, calcium signaling, and aging.