enzyme that catalyses the transfer of electrons from a reduced substrate or electron donor to an electron-accepting coenzyme; the transfer usually involves hydrogen. The equation for a dehydrogenase reaction is generally: reduced substrate + oxidized coenzyme ↔ oxidized product + reduced coenzyme. The reduced coenzyme is usually reoxidized in the *respiratory chain
. Dehydrogenases are classified according to the nature of the coenzyme, for example, those requiring the pyridine dinucleotide coenzymes NAD and NADP are termed pyridine-linked dehydrogenases, while those requiring FAD or FMN are termed flavin-linked dehydrogenases or flavoproteins.