title: Inactivation of chicken liver mevalonate 5-diphosphate decarboxylase by sulfhydryl-directed reagents: evidence of a functional dithiol.
abstract: Chicken liver mevalonate 5-diphosphate decarboxylase (ATP:(R)-5-diphosphomevalonate carboxy-lyase (dehydrating), EC 4.1.1.33) is inactivated by methylmethanethiosulfonate and 5,5'-dithiobis(2-nitrobenzoate). The presence of the substrates ATP or mevalonate 5-diphosphate protect very effectively against inactivation. The inactivation is second order with respect to methylmethanethiosulfonate, with an inactivation rate constant of (7.6 +/- 0.1).10(-5) microM-2.s-1, implying that the modifier may be reacting with more than one thiol in the enzyme. The enzyme is also inactivated by a number of dithiol-specific reagents, suggesting the presence of a functional dithiol. The determined pKapp values for enzyme modification by methyl methanethiosulfonate and phenylarsine oxide are 7.3 +/- 0.1 and 7.6 +/- 0.3, respectively. From the data presented, it is concluded that the enzyme possesses a functional dithiol that is important for substrate binding.
authors.affiliation: Departamento de Química, Facultad de Ciencia, Universidad de Santiago de Chile, Chile.
authors.forename: M
authors.initials: M
authors.lastname: Alvear
authors.forename: A M
authors.initials: AM
authors.lastname: Jabalquinto
authors.forename: E
authors.initials: E
authors.lastname: Cardemil
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001152:Arsenicals / Q000494:pharmacology; D002262:Carboxy-Lyases / Q000037:antagonists & inhibitors*; D002645:Chickens; D004228:Dithionitrobenzoic Acid / Q000494:pharmacology; D004229:Dithiothreitol / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008741:Methyl Methanesulfonate / Q000031:analogs & derivatives / Q000494:pharmacology; D008798:Mevalonic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D013439:Sulfhydryl Reagents / Q000494:pharmacology*; D014050:Toluene / Q000031:analogs & derivatives*
chemical_list: D001152:Arsenicals; D013439:Sulfhydryl Reagents; C029341:oxophenylarsine; C014674:methyl methanethiosulfonate; D014050:Toluene; C046285:5-diphosphomevalonic acid; D000255:Adenosine Triphosphate; D004228:Dithionitrobenzoic Acid; D008741:Methyl Methanesulfonate; D002262:Carboxy-Lyases; C022503:pyrophosphomevalonate decarboxylase; D008798:Mevalonic Acid; D004229:Dithiothreitol; C004848:dithiol