Mechanism-based active site modification of the soybean sterol methyltransferase by 26,27-dehydrocycloartenol

Bioorg Med Chem Lett. 2004 Jan 5;14(1):33-6. doi: 10.1016/j.bmcl.2003.10.015.

Abstract

26,27-dehydrocycloartenol (26,27-DHC) was shown to be a substrate for the soybean sterol methyltransferase (SMT) as well as a mechanism-based inhibitor of enzyme action. The K(m) and k(cat) for 26,27-DHC was 10 microM and 0.018 min(-1), respectively. SMT catalyzed 26,27-DHC to two products tentatively identified as 26-homocholesta-9,19-cyclo-23(24)E,26(26')-dienol and 26-homocholesta-9,19-cyclo-26(26')-en-3beta,24beta-diol by GC-MS. Inhibitor treatment was concentration- and time-dependent (pseudo-first-order kinetics). A replot of the half-lives for inactivation versus the inverse of the inactivator concentrations gave an apparent K(i) of 42 microM and a maximum rate of inactivation of 0.29 min(-1). A partition ratio (k(cat)/k(inact)) was calculated to be 0.06.

Publication types

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

MeSH terms

  • Binding Sites / drug effects
  • Binding Sites / physiology
  • Enzyme Inhibitors / chemistry
  • Enzyme Inhibitors / metabolism
  • Enzyme Inhibitors / pharmacology
  • Methyltransferases / antagonists & inhibitors*
  • Methyltransferases / metabolism*
  • Phytosterols / chemistry
  • Phytosterols / metabolism*
  • Phytosterols / pharmacology
  • Triterpenes

Substances

  • Enzyme Inhibitors
  • Phytosterols
  • Triterpenes
  • Methyltransferases
  • soysterol
  • cycloartenol