Transferases are enzymes that transfer a group, for example, the methyl group or a glycosyl group, from one compound (generally regarded as donor) to another compound (generally regarded as acceptor). The classification is based on the scheme 'donor:acceptor grouptransferase'. The common names are normally formed as 'acceptor grouptransferase' or 'donor grouptransferase'. In many cases, the donor is a cofactor (coenzyme) that carries the group to be transferred. The aminotransferases constitute a special case (EC 2.6).