Fumarate reductase is the enzyme that converts fumarate to succinate, and is important in microbial metabolism as a part of anaerobic respiration.^[1] The catalyzed reaction is:

succinate + acceptor <=> fumarate + reduced acceptor

Fumarate reductases can be divided into two classes depending on the electron acceptor:

• Fumarate reductase (NADH) (EC 1.3.1.6)

  The enzyme is monomeric and soluble, and can reduce fumarate independently from the electron transport chain.^[2] Fumarate reductase is absent from all mammalian cells.

• Fumarate reductase (quinol) (EC 1.3.5.4)

  The membrane-bound enzyme covalently linked to flavin cofactors, which is composed of 3 or 4 subunits, transfers electrons from a quinol to fumarate. This class of enzyme is thus involved in the production of ATP by oxidative phosphorylation.^[1]