Metabolism of N-hydroxy-2-acetylaminofluorene and N-hydroxy-phenacetin by guinea pig liver microsomal enzymes.

Deacylation has been proposed as a mechanism of activation of arylhydroxamic acids. In the present studies solubilized preparations from guinea pig liver microsomes, a source of high deacylase activity, were subjected to gel filtration on Sephacryl S-200. A single peak (peak I) of activity was found when column fractions were assayed colorimetrically for deacylation of N-hydroxy-2-acetylaminofluorene (N-OH-AAF). Corresponding to this peak were the following activities: binding of [3H-ring]-N-hydroxy-phenacetin (N-OH-P) to tRNA and deacylation of N-OH-P and N-OH-AAF, measured by the formation of nitrosophenetole (N = O-P) and nitrosofluorene (N = O-F), respectively. The binding of [3H-ring]-N-OH-AAF to tRNA was catalyzed by peak I, but to a greater extent by a second peak (II). The binding of both N-OH-P and N-OH-AAF to tRNA was inhibited by paraoxon, an esterase inhibitor. H.p.l.c. analysis revealed that for peak I, the major ether-extractable metabolites of N-OH-P and N-OH-AAF were the corresponding nitroso derivatives. In the presence of peak II, little metabolism to organic-extractable metabolites occurred. These data indicate that more than one mechanism is involved in the activation of N-OH-P and N-OH-AAF in this system, and that the difference in the activation of these arylhydroxamic acids cannot be explained by differences in the formation of deacylated metabolites.