Nicotinamide adenine dinucleotide (oxidized form: NAD+; reduced form: NADH) and nicotinamide adenine dinucleotide phosphate (oxidized form: NADP+; reduced form: NADPH) are two universal coenzymes functioning as hydride (H−) carriers at a standard reduction potential of −320 mV. The pair NAD+/NADH essentially works in oxidation reactions in catabolism (like synthesis of aldehyde and ketone functions from alcohols, or organic acids from aldehydes). On the contrary, the pair NADP+/NADPH serves as a reducing agent during anabolic processes (for example, in formation of saturated C-C bonds from double bonds). In addition to its role as an electron carrier, NAD+ also acts as an ADP-ribosyl donor.
The coenzyme NAD+ was formerly known as diphosphopyridine nucleotide (DPN) and NADP+ as triphosphopyridine nucleotide (TPN).