Activation and Inactivation of a Variety of Mutagenic Compounds by the Reconstituted System Containing Highly Purified Preparations of Cytochrome P-450 from Rat Liver

Abstract Six cytochrome P -450 preparations from phenobarbital (PB)-treated rats and two preparations from β-naphthoflavone (BNF)-treated rats were purified. Using Salmonella typhimurium TA98 the ability of these cytochrome P -450 preparations to mutagenically activate and inactivate a variety of carcinogens was examined. High- and low-spin forms of cytochrome P -448 isolated from BNF-treated rats (BNF-IIa and IId) activated various carcinogens. Both forms activated 2-aminofluorene, benzo[ a ]pyrene, and dibenz[ a,c ]anthracene. However, o -aminoazotoluene and 2-nitrofluorene were activated only by the low-spin form, and aflatoxin B 1 only by the high-spin form. In contrast, only limited carcinogens were activated by some preparations from PB-treated rats. 2-Aminofluorene was activated by four PB-inducible preparations (PB-Ia, Ic, Id, and IIa), but only moderately. Unexpectedly, however, the most prominent activation of benzo[ a ]pyrene was observed with one preparation (PB-Id) from PB-treated rats. Direct mutagens to the S. typhimurium , 4-NQO and AF-2, were markedly inactivated by NADPH-cytochrome c ( P -450) reductase without cytochrome P -450. One PB-inducible form (PB-Ic) inactivated 2-nitrofluorene, and the high-spin form of P -448 (BNF-IIa) inactivated AF-2.