Mechanism of reaction, tissue distribution, and inhibition of arylhydroxamic acid acyltransferase.

The enzyme of rat liver that can transform /V-hydroxy-/V2-fluorenyIacetamide into a reactive derivative capable of introducing fluorenylamine groups into nucleic acids has been shown to be a sulfhydryl-dependent enzyme with a molecular weight of approximately 28,000. A 30-fold purifi cation of the enzyme from 105,000 x g supernatants of liver has been achieved by precipitation with ammonium sulfate and gel nitration on Sephadex G-100. Evidence that this mechanism of activation involves transfer of the /V-acetyl group to the oxygen of the hydroxylamine came from experiments that showed that O-methylation of /V-hydroxy/V-2-fluorenylacetamide prevented activation of the hydroxamic acid. Distribution studies demonstrated considerable acyltransferase activity in kidney, stomach, small intestine, and colon; lung and spleen were less active; and blood, brain, and muscle were essentially without activity. Tissue distribution studies and protein purification exper iments utilizing ammonium sulfate precipitation and gel filtration techniques disclosed that the enzyme responsible for the activation of /V-hydroxy-/V-2-fluorenylacetamide was inseparable from the enzyme that transfers the acetyl group of /V-hydroxy-/V-2-fluorenylacetamide to 4aminoazobenzene. Acyltransferase-catalyzed activation of /V-hydroxy-/V2-fluorenylpropionamide demonstrated that the activation of hydroxamic acids was not restricted to acetylated derivatives. Hepatic acyltransferase-catalyzed formation of fluorenylamine-substituted nucleic acid was inhibited by both arylamines and arylacetamides. This inhibition, considered with previous reports of the inhibition of A/-hydroxy-/V2-fluorenylacetamide hepatocarcinogenesis by acetanilide and /7-hydroxyacetanilide, suggest that acyltransferase-cat alyzed activation of arylhydroxamic acids may be involved in the formation of liver tumors. INTRODUCTION