Formation of electrophilic N-acetoxyarylamines in cytosols from rat mammary gland and other tissues by trans-acetylation from the carcinogen N-hydroxy-4-acetylaminobiphenyl

Abstract

The 105 000 × g supernatant fractions of various rat tissues catalyze the transfer of the N-acetyl group of certain carcinogenic aromatic acethydroxamic acids to the O atom of aromatic hydroxylamines. The resulting N-acetoxyhydroxylamines are strongly electrophilic and have been detected and analyzed through their reaction with N-acetylmethionine to yield methylmercaptoaminoarenes. Of the rat tissues studied the liver had the highest activity; kidney and small intestinal mucosa were about 15–20% as active. The transacetylase activities of these tissues were similar with respect to their ability to use either N-hydroxy-2-acetylaminofluorene ( N-hydroxy-AAF or N-hydroxy-4-acetylaminobiphenyl ( N-hydroxy-AABP) as acetyl donors, their stability on storage at 2–3°C, and their elution patterns from Sephadex G-100 columns. Low transacetylase activity was found in spleen and muscle. Mammary tissue from 16–21 day pregnant rats had 20% of the transacetylase activity of rat liver when N-hydroxy-AABP was used as acetyl donor and N-hydroxy-4-aminobiphenyl ( N-hydroxy-ABP) was the acetyl acceptor. This enzyme system from mammary tissue did not utilize the fluorene derivatives as either acetyl donor or acetyl acceptor, was much more labile than the liver, kidney, or intestinal mucosa systems, and had a pH optimum at 7.5, as compared to pH 6.8 for liver. The mammary tissue system was similar to the hepatic system in being inhibited by sulfhydryl reagents; it required a source of reduced pyridine nucleotides for maximum activity.