title: Monoclonal antibodies distinguish among isozymes of the cytochrome P-450b subfamily.
abstract: Polyclonal antibody has been shown previously to react identically with cytochromes P-450b and P-450e purified from Long Evans rats and a strain variant of cytochrome P-450b purified from Holtzman rats (P-450bH). In the present study, an array of 12 different monoclonal antibodies produced against cytochrome P-450b has been used to distinguish among these closely related phenobarbital-inducible rat hepatic cytochromes P-450. In immunoblots and enzyme-linked immunosorbent assays, 10 monoclonal antibodies bind to cytochromes P-450b, P-450e, and P-450bH; one monoclonal antibody (B50) recognizes cytochromes P-450b and P-450bH but not cytochrome P-450e; and one monoclonal antibody (B51) is specific for cytochrome P-450b. In addition, one monoclonal antibody (BEF29) reacts strongly with cytochrome P-450f, and another antibody (BEA33) reacts weakly with cytochrome P-450a. No cross-reactions with cytochromes P-450c, P-450d, and P-450g-P-450j were detected with any of the monoclonal antibodies in these assays. Six spatially distinct epitopes on cytochrome P-450b were identified, and differences in antibody reactivity provided evidence for three additional overlapping epitopes. Several monoclonal antibodies are potent inhibitors of testosterone and benzphetamine metabolism supported by cytochrome P-450b in a reconstituted system. B50 and BE52 do not inhibit metabolism of the two substrates by microsomes from untreated rats, but inhibit benzphetamine N-demethylation and testosterone metabolism to 16 alpha- and 16 beta-hydroxytestosterone as well as androstenedione formation 67-94% by microsomes from phenobarbital-treated rats. No other pathways of testosterone metabolism are inhibited by these monoclonal antibodies. The differential inhibition of microsomal metabolism of benzphetamine and testosterone by these monoclonal antibodies is a reflection of the content and inducibility of cytochromes P-450b and P-450e as well as other cytochrome P-450 isozymes.
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000302:isolation & purification; D001589:Benzphetamine / Q000378:metabolism; D003577:Cytochrome P-450 Enzyme System / Q000032:analysis*; D004797:Enzyme-Linked Immunosorbent Assay; D005779:Immunodiffusion; D007527:Isoenzymes / Q000032:analysis* / Q000276:immunology; D008862:Microsomes, Liver / Q000378:metabolism*; D008970:Molecular Weight; D051381:Rats; D011919:Rats, Inbred Strains; D013045:Species Specificity
chemical_list: D000911:Antibodies, Monoclonal; D007527:Isoenzymes; D001589:Benzphetamine; D003577:Cytochrome P-450 Enzyme System