A high-spin form of cytochrome P-450 highly purified from polychlorinated biphenyl-treated rats. Catalytic characterization and immunochemical quantitation in liver microsomes.

A high-spin form of cytochrome P-450 (termed PCB P-448-H) was purified from liver microsomes of polychlorinated biphenyl (PCB)-treated rats to homogeneity as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. This high-spin form of cytochrome P-450 was distinguishable from a low-spin form of cytochrome P-450 (PCB P-448-L) purified from microsomes of PCB-treated rats by the criteria of molecular weights, peptide mapping, and immunochemical properties. In addition, PCB P-448-H catalyzed the hydroxylation of acetanilide (position 4) and biphenyl (positions 2 and 4), and N-hydroxylation of the promutagens 3-amino-1-methyl-5H-pyrido(4,3-b)indole (Trp-P-2), 2-amino-6-methyl-dipyrido(1,2-alpha:3',2'-d)imidazole (Glu-P-1), 2-aminofluorene, and 4-aminobiphenyl at much faster rates than did PCB P-448-L. These promutagens and aflatoxin B1 were efficiently metabolized to mutagens by this high-spin form of hemoprotein. Rabbit immunoglobulin G (IgG) raised against PCB P-448-H inhibited the microsomal O-depropylation activity of p-propoxyaniline. Radial immunodiffusion assay with the IgG showed that PCB P-448-H was one of the major forms of cytochrome P-450 in liver microsomes of PCB-treated rats. On the basis of these results, we propose that this high-spin form of cytochrome P-450 is a key enzyme activating a variety of environmental promutagens in the 9000 x g supernatant fraction of PCB-treated rats, which has been widely used as an activation system in routine mutation tests.