Nicotinamide adenine dinucleotide (
NAD) is a
coenzyme found in all living
cells. The compound is a dinucleotide, because it consists of two
nucleotides joined through their phosphate groups. One nucleotide contains an
adenine base and the other
nicotinamide. Nicotinamide adenine dinucleotide exists in two forms, an
oxidized and
reduced form abbreviated as
NAD and
NADH respectively.