2-Acetylaminofluorene induces the level of cytochrome P-450 in rat liver microsomes by 50% (p < 0.001). This induced cytochrome(s) was characterized and compared to the major forms of cytochrome P-450 induced by phenobarbital and 3-methylcholanthrene. The properties investigated were: the absorption maximum of the complex formed between reduced cytochrome P-450 and carbon monoxide; the substrate specificities using aminopyrine, benzphetamine, ethylmorphine, benzo(a)pyrene, ethoxycoumarin, ethoxyresorufin, and 2-acetylaminofluorene itself as substrates; metabolite patterns with benzo(a)pyrene and 2-acetylaminofluorene; sensitivity to different inhibitors; binding spectra with aniline and hexobarbital; and molecular weight as determined by sodium dodecyl sulfate:disc gel electrophoresis. The results indicate that 2-acetylaminofluorene induces a form(s) of cytochrome P-450 especially effective in the metabolism of this substance itself (i.e., the process can be called substrate induction) and different from the major forms of cytochrome P-450 induced by phenobarbital and 3-methylcholanthrene.

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These studies were supported by grants from the Swedish Medical Research Council and the Swedish Natural Science Research Council.

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