Specificity of 17β-oestradiol and benzo[α]pyrene oxidation by polymorphic human cytochrome P4501B1 variants substituted at residues 48, 119 and 432

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Abstract
1. Eight human cytochrome P4501B1 (CYP1B1) allelic variants, namely Arg48Ala119Leu432, Arg48Ala119Val432, Gly48Ala119Leu432, Gly48Ala119Val432, Arg48Ser119Leu432, Arg48Ser119Val432, Gly48Ser119Leu432 and Gly48Ser119Val432 (all with Asn453), were expressed in Escherichia coli together with human NADPH-P450 reductase and their catalytic specificities towards oxidation of 17β-oestradiol and benzo[α]pyrene were determined. 2. All of the CYP1B1 variants expressed in bacterial membranes showed Fe2+·CO versus Fe2+ difference spectra with wavelength maxima at 446nm and they reacted with antibodies raised against recombinant human CYP1B1 in immunoblots. The ratio of expression of the reductase to CYP1B1 in these eight preparations ranged from 0.2 to 0.5. 3. CYP1B1 Arg48 variants tended to have higher activities for 17β-oestradiol 4-hydroxylation than Gly48 variants, although there were no significant variations in 17β-oestradiol 2-hydroxylation activity in these eight CYP1B1 variants. Interestingly, ratios of formation of 17β-oestradiol 4-hydroxylation to 2-hydroxylation by these CYP1B1 variants were higher in all of the Val432 forms than the corresponding Leu432 forms. 4. In contrast, Leu432 forms of CYP1B1 showed higher rates of oxidation of benzo[α]pyrene (to the 7,8-dihydoxy-7,8-dihydrodiol in the presence of epoxide hydrolase) than did the Val432 forms. 5. These results suggest that polymorphic human CYP1B1 variants may cause some altered catalytic specificity with 17β-oestradiol and benzo[α]pyrene and may influence susceptibilities of individuals towards endogenous and exogenous carcinogens.

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