Nicotinamide adenine dinucleotide

Nicotinamide adenine dinucleotide (NAD) is a coenzyme that transfers electrons in cellular redox reactions and serves as a substrate for enzymes involved in signaling and metabolism.

NAD⁺/NADH redox couple: The interconvertible oxidized and reduced forms of NAD that carry electrons in metabolism. NAD⁺ accepts a hydride to become NADH, which can later donate reducing power.
Nicotinamide: A pyridine-carboxamide compound that forms the reactive end of NAD’s redox-active ring. The nicotinamide ring accepts or donates the hydride during NAD-dependent redox reactions.
Glycolysis: A metabolic pathway that converts glucose into pyruvate while producing ATP and NADH. Glycolysis reduces NAD⁺ during the oxidation of glyceraldehyde 3-phosphate.
Nicotinamide adenine dinucleotide phosphate: A phosphorylated NAD-related coenzyme that commonly supplies reducing power for biosynthesis and antioxidant defense. NADP’s extra phosphate distinguishes it from NAD and helps enzymes select between them.
Hydride transfer: A chemical reaction in which a hydrogen atom transfers with both bonding electrons as a hydride ion. NAD-dependent enzymes commonly transfer a hydride between NAD and a metabolic substrate.
Adenosine diphosphate: A nucleotide consisting of adenine, ribose, and two phosphate groups. NAD contains an ADP-derived moiety that helps enzymes recognize and bind the cofactor.
Citric acid cycle: A cyclic pathway that oxidizes acetyl-CoA and generates reduced electron carriers. Several cycle reactions reduce NAD⁺ to NADH as carbon is oxidized.
Flavin adenine dinucleotide: A redox coenzyme whose flavin group can accept one or two electrons in enzyme reactions. FAD is another major electron carrier, but its flavin chemistry differs from NAD’s nicotinamide chemistry.
NAD kinase: An enzyme that phosphorylates NAD to produce NADP. This modification creates NADP, a related cofactor used in distinct redox pathways.
Nicotinamide riboside: A nucleoside composed of nicotinamide and ribose that can serve as a precursor to NAD. Cells can build NAD from this nicotinamide-containing salvage-pathway intermediate.

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