Cytochrome P-450 in Human Liver Microsomes: High-Performance Liquid Chromatographic Isolation of Three Forms and Their Characterization1

Abstract

Three forms of cytochrome P-450, designated as P-450-HM1, P-450-HM2, and P-450-HM3, were isolated from human liver microsomes using high-performance liquid chromntography (HPLC) techniques. Each purified preparation showed a single protein band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). From the results of SDS-PAGE, the molecular weights of P-450-HM1, P-450-HM2, and P-450-HM3 were estimated to be 51,000, 54,000, and 52,000, respectively. The oxidized absolute spectra of these three forms of cytochrome P-450 showed Soret absorption peaks at around 417 nm, indicating that these forms were in, the low spin state. In a reconstituted system, P-450-HM1 showed the highest catalytic activities of nifedipine and (S)- or (R)-nilvadipine oxidases. The same form showed higher activities of testosterone 6β-hydroxylase and progesterone 6β- and 16α-hydroxylases. P-450-HM2 showed high N-demethylase activities for benzphetamine and aminopyrine, and also showed the highest activity of testosterone 16β-hydroxylase among the three forms, while it did not show detectable activities of testosterone 6β-hydroxylase and progesterone 6β- and 16α-hydroxylases. Anti-P-450- HM1 immunoglobulin G (IgG), but not anti-P-450-HM2 IgG, inhibited the activities of testosterone 6β-hydroxylase and nifedipine and nilvadipine oxidases in human liver microsomes. Anti-P-450-HM1 IgG was also inhibitory against progesterone 6β- and 16α-hydroxylases. Amino-terminal sequences of P-450-HM1, P-450-HM2, and P-450-HM3 were homologous to those of P-450_NF, P-450_MP, and P-450 HFLa, respectively, though dissimilarities in the nature of the purified forms from the reported data were noted.