Catechol-O-methyltrasferase (COMT) is an enzyme that catalyses the transfer of the methyl group of Sadenosylmethionine (SAM) into catechol substrates such as levodopa, dopamine, epinephrine, and norepinephirine in the presence of Mg2+. COMT appears to be located in the postsynaptic neuron and plays roles in the metabolism of catechol estrogens and the inactivation of catecholamine neurotransmitters though enzymatic degradation.