Fumarate hydratase, mitochondrial is also known as Fumarase or FH, which belongs to the class-II fumarase/aspartase family and Fumarase subfamily. Fumarase is a homotetramer protein which is expressed in red blood cells. There are two substrate-binding sites: the catalytic A site, and the non-catalytic B site that may play a role in the transfer of substrate or product between the active site and the solvent. Alternatively, the B site may bind allosteric effectors. Fumarase also acts as a tumor suppressor.