Oxidoreductases (Molecular Biology)

Oxidoreductases form a large class of enzymes that catalyze the oxidation of one substrate, with the concomitant reduction of another. For these donor-acceptor reactions, the electron acceptor may be a pyridine nucleotide (eg, NAD), cytochrome, oxygen, quinone or others. The term dehydrogenase is used to describe oxidation-reduction reactions whenever possible, whereas the term oxidase is restricted to enzymes for which oxygen is an acceptor. Dehydrogenases act on primary and secondary alcohols, as well as hemiacetals. They also convert aldehydes to the corresponding acids, and these reactions may involve phosphorylation of the acid or acetylation of coenzyme A (CoA). Oxo groups may be oxidized by the addition of water, followed by the cleavage of a C Cbond or dehydrogenation. Dehydrogenases can introduce double bonds by direct dehydrogenation at a single C Cbond. They function as oxidases by utilizing oxygen for the deamination of amino acids that can also undergo direct dehydrogenation reactions. In addition, they can dehydrogenate secondary amines to form C=redouble bonds and oxidize NADH or NADPH as well as nitrogenous substrates and donors with sulfur or heme groups.