title: Kinetics and inhibition studies of catechol O-methyltransferase from the yeast Candida tropicalis.
abstract: The Kms for esculetin and S-adenosyl-L-methionine for catechol O-methyltransferase from the yeast Candida tropicalis were 6.2 and 40 microM, respectively. S-Adenosyl-L-homocysteine was a very potent competitive inhibitor with respect to S-adenosyl-L-methionine, with a Ki of 6.9 microM. Of the catechol-related inhibitors, purpurogallin, with a Ki of 0.07 microM, showed the greatest inhibitory effect. Sulfhydryl group-blocking reagents, such as thiol-oxidizing 2-iodosobenzoic acid and mercaptide-forming p-chloromercuribenzoic acid, provided evidence for sulfhydryl groups in the active site of the enzyme. Yeast catechol O-methyltransferase is a metal-dependent enzyme and requires Mg2+ for full activity. Zn2+ and Mn2+ but not Ca2+ were able to substitute for Mg2+. Mn2+ showed optimal enzyme activation at concentrations 50- to 100-fold lower than those of Mg2+.
mesh_terms: D001567:Benzocycloheptenes / Q000494:pharmacology; D002175:Candida / Q000201:enzymology*; D002394:Catechol O-Methyltransferase / Q000378:metabolism*; D065098:Catechol O-Methyltransferase Inhibitors; D004789:Enzyme Activation / Q000187:drug effects; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008345:Manganese / Q000494:pharmacology; D012435:S-Adenosylhomocysteine / Q000494:pharmacology; D012436:S-Adenosylmethionine / Q000378:metabolism; D013439:Sulfhydryl Reagents / Q000494:pharmacology; D014468:Umbelliferones / Q000378:metabolism; D015032:Zinc / Q000494:pharmacology
chemical_list: D001567:Benzocycloheptenes; D065098:Catechol O-Methyltransferase Inhibitors; D013439:Sulfhydryl Reagents; D014468:Umbelliferones; D008345:Manganese; D012436:S-Adenosylmethionine; D012435:S-Adenosylhomocysteine; D002394:Catechol O-Methyltransferase; D008274:Magnesium; D015032:Zinc; C026133:purpurogallin; C007628:esculetin