CATECHOL O-METHYLTRANSFERASE ACTIVITY IN THE HUMAN PLACENTA AND LIVER

Catechol O-melthyltransferase (COMT) obtained from human liver (HL) and human placenta (HP) was found to be much less active than rat liver (RL) COMT when norepronephrine, epinephrine, dopamine, and isoproterenol are used as substrates. The K(m) values, which reflect the affinity of substrate and enzyme, show that RL COMT has the highest affinity toward the catecholamine substrates followed by HP COMT and then HL COMT. Both HP and RL COMT preparations O-methylate the catecholamines primarily in the meta position.