MUTAGENIC ACTIVATION OF 3-METHOXY-4-AMINOAZOBENZENE BY MOUSE RENAL CYTOCHROME-P450 CYP4B1 - CLONING AND CHARACTERIZATION OF MOUSE CYP4B1

A new P450 responsible for mutagenic activation of 3-methoxy-4-aminoaz obenzene (3-MeO-AAB) which is a potent procarcinogen was purified from renal microsomes of male mice using an index of umu gene expression. The purified P450 had high bioactivation toward 3-MeO-AAB and also 2-a minofluorene and 2-aminoanthracene. The antibody against this P450 com pletely inhibited mutagenic activation of 3-MeO-AAB of mouse renal mic rosomes. With immunoblotting, this form was present abundantly in rena l microsomes of male mice but not in those of female mice, This P450 w as also present in pulmonary microsomes of male and female mice but no t in hepatic microsomes, The NH2-terminal amino acid sequence analysis indicated that this form belonged to the CYP4B subfamily, Thus, mouse kidney cDNA library was screened with rat CYP4B1 probe. The cDNA-dedu ced amino acid sequence of isolated cDNA consisted of 511 amino acids and bore 90, 86, and 84% similarities to rat, rabbit, and human CYP4B1 , respectively. The NH2-terminal amino acid sequence of the purified r enal P450 and amino acid sequence of BrCN-digested peptides from the p urified P450 agreed with the cDNA-deduced amino acid sequence, These r esults suggest that CYP4B1 is a major form in renal microsomes of male mice and plays a major role in mutagenic activation of 3-MeO-AAB. In extrahepatic tissue, CYP4B1 may contribute to chemical carcinogenesis. (C) 1995 Academic Press, Inc.