In vitro metabolism and metabolic activation of 2-acetylaminofluorene (AAF), 2-aminofluorene, and 2,4-diaminoanisole to mutagenic (Salmonella test system) and covalently proteinbound intermediates were evaluated in subcellular fractions from seven human livers. The cytochrome P-450 content, aryl hydrocarbon hydroxylase activity, and sodium dodecyl sulfate: polyacrylamide gel electrophoresis of the human liver microsomes were concomitantly studied. AAF was extensively me tabolized (both C-and

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... hydroxylated) by all of the human liver microsomal samples, but severalfold variations between the individual metabolites were observed among the different mi crosomal fractions. Similar variation was also observed for aryl hydrocarbon hydroxylase activity. Electrophoresis of the mi crosomal fractions revealed several polypeptides with a molec ular weight range of 40,000 to 60,000. Two of these polypep tides, with molecular weights of approximately 54,000 and 55,000, correspond to those seen in rat liver microsomes following pretreatment with 3-methylcholanthrene. The in vitro mutagenicity of AAF with the individual samples corresponded well with those of 2-aminofluorene and 2,4-diaminoanisole, as did the degree of AAF /V-hydroxylation. A/-Hydroxy-2-acetylaminofluorene was converted to mutagen(s) by both human liver microsomal and cytosol fractions, presumably via deacetylation. A poor association between the extent of covalent binding of AAF to liver microsomal proteins and the degree of mutagenicity in the Salmonella system was observed among the samples, possibly indicating that the reactive metabolite(s) arylating the protein differs from that causing the frame-shift mutation in the Salmonella. The results from the . present study on AAF and benzo(a)pyrene hydroxylation; the metabolic activation of AAF, 2-aminofluorene, and 2,4-diaminoanisole; as well as the electrophoretic characterization of hepatic cytochrome P-450 in dicate great qualitative similarities between the subcellular fractions from human liver and those from the rat, the mouse, and the rhesus monkey.