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Bromopyruvate is an alkylating agent of pigeon liver malic enzyme (malate dehydrogenase (decarboxylating), EC 1.1.1.40). It combines first with the enzyme to give an enzyme-bromopyruvate complex, then reacts with a proximal -SH group, resulting in the formation of a pyruvate derivative. Bromopyruvate is also a substrate for the reductase partial reaction, and a non-competitive inhibitor of L-malate in the overall oxidative decarboxylase reaction catalyzed by this enzyme. Modification of the -SH group by this compound is accompanied by concomitant loss of both oxidative decarboxylase activity and reductase activity on bromopyruvate. Inactivation of the overall activity is partially prevented by NADP+ or NADPH, singly or in combination with L-malate.

SummaryThe induction of hepatic methionine adenosyltransferase by adrenal cortical hormones has been studied in adrenalectomized rats. Experiments with cortisol, cortisone, corticosterone, prednisolone, and triamcinolone revealed that triamcinolone was the most potent inducer of methionine adenosyltransferase activity. On the contrary, two mineral corticoids, aldosterone and deoxycorticosterone, and a biologically inactive isomer of cortisol, 11-epicortisol, were found to be ineffective in raising the hepatic level of this enzyme, indicating the specificity of the action of glucocorticoids in this respect. Actinomycin, puromycin, and cycloheximide, inhibitors of RNA or protein synthesis, largely blocked the glucocorticoid-induced increase in the enzyme, observed 12 hours after hormone administration. The results suggest that the changes in the hepatic levels of methionine adenosyltransferase brought about by glucocorticoids represent enzyme synthesis de novo probably involving enhanced DNA-directed RNA pr...