Oxidoreductase

In biochemistry, an oxidoreductase is an enzyme that catalyzes the transfer of electrons from one molecule, the reductant, also called the electron donor, to another, the oxidant, also called the electron acceptor. This group of enzymes usually utilizes NADP+ or NAD+ as cofactors. Transmembrane oxidoreductases create electron transport chains in bacteria, chloroplasts and mitochondria, including respiratory complexes I, II and III. Some others can associate with biological membranes as peripheral membrane proteins or be anchored to the membranes through a single transmembrane helix.

For example, an enzyme that catalyzed this reaction would be an oxidoreductase:

In this example, A is the reductant (electron donor) and B is the oxidant (electron acceptor).

In biochemical reactions, the redox reactions are sometimes more difficult to see, such as this reaction from glycolysis:

In this reaction, NAD⁺ is the oxidant (electron acceptor), and glyceraldehyde-3-phosphate is the reductant (electron donor).

Proper names of oxidoreductases are formed as "donor:acceptor oxidoreductase"; however, other names are much more common.^{[citation needed]}

Oxidoreductases are classified as EC 1 in the EC number classification of enzymes. Oxidoreductases can be further classified into 21 subclasses: