Kinetic reaction mechanism for magnesium binding to membrane-bound and soluble catechol O-methyltransferase

Biochemistry. 1987 May 19;26(10):2955-8. doi: 10.1021/bi00384a042.


Catechol O-methyltransferase (COMT, EC 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.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Brain / enzymology*
  • Catechol O-Methyltransferase / isolation & purification
  • Catechol O-Methyltransferase / metabolism*
  • Cell Membrane / enzymology
  • Cytosol / enzymology
  • Humans
  • Isoenzymes / isolation & purification
  • Isoenzymes / metabolism*
  • Kinetics
  • Magnesium / metabolism*
  • Models, Biological
  • Molecular Weight


  • Isoenzymes
  • Catechol O-Methyltransferase
  • Magnesium