title: Use of a monoclonal antibody specific for rabbit microsomal cytochrome P-450 3b to characterize the participation of this cytochrome in the microsomal 6 beta- and 16 alpha-hydroxylation of progesterone.
abstract: A monoclonal antibody was developed that is specific for the 3b electrophoretic class of rabbit liver microsomal cytochrome P-450 as judged by immunoprecipitation and subsequent electrophoretic analysis. The antibody is inhibitory of catalytically distinct, variant forms of P-450 3b prepared from New Zealand White or IIIVO/J rabbits, respectively. Peptide mapping of the immunopurified P-450 3b from NZW and IIIVO/J microsomes indicates that a characteristic difference between the variant forms is exhibited by the antigen. In addition, a competitive assay indicates that the binding properties of the antibody do not differ substantially toward the variant forms of P-450 3b. The inhibitory antibody was used to examine the contribution of P-450 3b to the microsomal 16 alpha- and 6 beta-hydroxylation of progesterone. The antibody inhibits 40-70% of the 16 alpha-hydroxylase activity of microsomes from either New Zealand White or IIIVO/J rabbits. In contrast, it does not inhibit 6 beta-hydroxylation catalyzed by microsomes prepared from strain IIIVO/J but does inhibit this reaction as catalyzed by microsomes from most New Zealand White rabbits. The antibody also inhibits the increased 16 alpha-hydroxylase activity of IIIVO/J microsomes observed in the presence of 5 beta-pregnane-3 beta,20 alpha-diol, an allosteric effector of this variant form of P-450 3b. Use of this monoclonal antibody provides a link between the observed properties of the purified, variant forms of P-450 3b and microsomal metabolism. These results indicate that the antibody can be used to phenotype variant forms of P-450 3b in microsomal fractions.
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal; D001189:Aryl Hydrocarbon Hydroxylases; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D000072467:Cytochrome P450 Family 2; D000939:Epitopes / Q000032:analysis*; D005260:Female; D014644:Genetic Variation; D006825:Hybridomas / Q000276:immunology; D006900:Hydroxylation; D007700:Kinetics; D051379:Mice; D008807:Mice, Inbred BALB C; D008862:Microsomes, Liver / Q000378:metabolism*; D010446:Peptide Fragments / Q000032:analysis; D011374:Progesterone / Q000378:metabolism*; D011817:Rabbits; D039181:Steroid 16-alpha-Hydroxylase
chemical_list: D000911:Antibodies, Monoclonal; D000939:Epitopes; D010446:Peptide Fragments; D011374:Progesterone; D003577:Cytochrome P-450 Enzyme System; D001189:Aryl Hydrocarbon Hydroxylases; C450239:CYP2C3 protein, Oryctolagus cuniculus; D000072467:Cytochrome P450 Family 2; D039181:Steroid 16-alpha-Hydroxylase