Cytochrome P-450 in human fetal liver. Properties of P-450 HFLa,a form of cytochrome P-450 in human fetal livers

One of the major forms of cytochrome P-450, named P-450 HFLa, of human fetal livers was purified and characterized. The cytochrome P-450 preparation had an apparent molecular weight of 51,500 as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. N-Terminal amino acid sequence of P-450 HFLa was similar but not identical to that of P-450NF involved in nifedipine oxidation in adult human livers. P-450 HFLa catalyzed 16 alpha-hydroxylation of dehydroepiandrosterone 3-sulfate (DHEA-sulfate) in a reconstituted system. The concentration of P-450 HFLa in liver homogenates from human fetuses highly correlated with the activity of DHEA-sulfate 16 alpha-hydroxylase. Furthermore, anti-P-450 HFLa antibodies inhibited the 16 alpha-hydroxylation. P-450 HFLa was also found to catalyze the mutagenic activation of aflatoxin B1 (AFB1) and 2-amino-3-methylimidazo[4,5-f]quinoline (IQ). The antibodies to P-450 HFLa inhibited efficiently the mutagen-producing activities from AFB1 and IQ in human fetal livers. The nucleotide and the deduced amino acid sequences of lambda HFL33 containing the entire coding region for a form of cytochrome P-450 related to P-450 HFLa, were highly similar to but clearly distinct from those of NF25 and HLp complementary deoxyribonucleic acids. The oligonucleotide probes specific to the coding and 3'-noncoding region of lambda HFL 33 (oli-HFL and oli-HFL3', respectively) gave hybridizable bands with ribonucleic acid (RNA) from fetal but not adult livers. In contrast, an oligonucleotide probe specific to the coding region of NF 25 and HLp (oli-NF) gave hybridizable bands with RNA from only adult but not fetal livers.