Biogenic amine metabolism in Biomphalaria glabrata I. Catechol-O-methyltransferase activity

In contrast to mammalian tissues, catechol-O-methyltransferase (COMT) activity is localized predominantly, if not entirely, in the cytosolic fraction in the tissues of Biomphalaria glabrata. Enzymatic activity is greater in glycylglycine and Tris-Cl buffers than in phosphate buffer. The pH optimum for this enzymatic reaction is 8.5. The catalysis is stimulated by magnesium ion, other divalent cations are less effective in this reaction. The Km values for 3,4-dihydroxybenzoate and S-adenosylmethionine have been determined to be 100 microM and 8 microM respectively. The product of the COMT reaction has been characterized by thin-layer chromatography. The specific activity of COMT is highest in the ovotestes area and lowest in the brain, whereas the total activity is maximal in the hepatopancreas followed by head--foot, ovotestes and brain.