Immunochemical detection of human liver cytochrome P450 forms related to phenobarbital-inducible forms in the mouse

Polyclonal antibodies generated to four distinct mouse liver phenobarbital-inducible cytochrome P450 isoforms were used to analyse related forms in human liver. N-terminal sequence analysis and biochemical properties of the P450s used as antigens suggest that they belong to P450 subfamilies IIB (P450PBI), IA (P450PBII), IIC (P450PBIII) and IIA (P450Coh). In immunoblot analysis, anti-P450PBII detected a single protein presumed to be P450IA2 in all the human livers tested. No proteins corresponding with P450IA1 could be detected. Anti-PBIII and anti-P450Coh antibodies each detected one band (54 and 48 kDa, respectively) in the liver samples. No bands were revealed by anti-P450PBI antibody. Protein dot-immunobinding analysis showed that P450s immunodetectable by anti-P450PBII, anti-P450PBIII and anti-P450Coh antibodies are expressed in human liver (range 9 to 69 pmol P450/mg protein). In immunoinhibition experiments the activity of 7-ethoxyresorutin O-deethylase (EROD) was blocked up to 90% by the anti-P450PBII antibody. Aryl hydrocarbon hydroxylase (AHH) was inhibited only by anti-P450PBIII, and coumarin 7-hydroxylase (COH) only by anti-P450Coh antibody. Testosterone hydroxylations in positions 6 beta, 7 alpha, 15 alpha and 16 alpha were not affected significantly by any of the antibodies. These data suggest that the human liver P450IA2 is responsible for most of the elevated EROD activity, P450s in the IIC subfamily for constitutive AHH and P450s in the IIA subfamily for all of COH activity.