Mechanism of substrate inactivation of Escherichia coli S-adenosylmethionine decarboxylase.
S-Adenosylmethionine decarboxylase, a pyruvoyl-containing decarboxylase, is inactivated in a time-dependent process under turnover conditions. The inactivation is dependent on the presence of both substrate and Mg2+, which is also required for enzyme activity. The rate of inactivation is dependent on the concentration of substrate and appears to be saturable. Inactivation by [methionyl-3,4-14C]-adenosylmethionine results in stoichiometric labeling of the protein. In contrast, when either S-[methyl-3H]adenosylmethionine or [8-14C]adenosylmethionine is used, there is virtually no incorporation of radioactivity. Automated Edman degradation of the alpha (pyruvoyl-containing) subunit reveals that substrate inactivation results in the conversion of the pyruvoyl group to an alanyl residue. These data suggest a mechanism of inactivation which involves the transamination of the nascent product to the pyruvoyl group, followed by the elimination of methylthioadenosine and the generation of a 2-propenal equivalent which could undergo a Michael addition to the enzyme. This is the first evidence for a transamination mechanism for substrate inactivation of a pyruvoyl enzyme.
Anton
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DL
Central Research and Development Department, Experimental Station, E. I. du Pont de Nemours and Company, Wilmington, Delaware 19898.
Kutny
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D012437:Adenosylmethionine Decarboxylase / Q000037:antagonists & inhibitors*; D002262:Carboxy-Lyases / Q000037:antagonists & inhibitors*; D004926:Escherichia coli / Q000201:enzymology*; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D012436:S-Adenosylmethionine / Q000494:pharmacology
D012436:S-Adenosylmethionine; D002262:Carboxy-Lyases; D012437:Adenosylmethionine Decarboxylase; D008274:Magnesium