title: Kinetic reaction mechanism for magnesium binding to membrane-bound and soluble catechol O-methyltransferase.
abstract: Catechol O-methyltransferase (COMT, EC 2.1.1.6) from human brain occurs in both a membrane-bound (MB-COMT) and a soluble form (SOL-COMT). While these enzymes appear to be distinct molecular entities, both catalyze the O-methylation of catecholamines through an ordered reaction mechanism in which S-adenosylmethionine (SAM) is the leading substrate [Rivett, A. J., & Roth, J. A. (1982) Biochemistry 21, 1740-1742; Jeffery, D. R., & Roth, J. A. (1985) J. Neurochem. 44, 881-885]. Both MB-COMT and SOL-COMT require the presence of divalent cations for catalytic activity. This series of experiments provides evidence indicating that magnesium ions bind to both MB-COMT and SOL-COMT in a rapid equilibrium sequence prior to the addition of SAM. An equation is presented that predicts the qualitative results obtained in all kinetic experiments carried out with either MB-COMT or SOL-COMT.
mesh_terms: D001921:Brain / Q000201:enzymology*; D002394:Catechol O-Methyltransferase / Q000302:isolation & purification / Q000378:metabolism*; D002462:Cell Membrane / Q000201:enzymology; D003600:Cytosol / Q000201:enzymology; D006801:Humans; D007527:Isoenzymes / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism*; D008954:Models, Biological; D008970:Molecular Weight
chemical_list: D007527:Isoenzymes; D002394:Catechol O-Methyltransferase; D008274:Magnesium