title: Absence of hepatic cytochrome P450bufI causes genetically deficient debrisoquine oxidation in man.
abstract: The common genetic deficiency of drug oxidation known as debrisoquine/sparteine-type polymorphism was investigated with bufuralol as prototype substrate. In human liver microsomes the 1'-hydroxylation of bufuralol is catalyzed by two functionally distinct P-450 isozymes, the high-affinity/highly stereoselective P450bufI and the low-affinity/nonstereoselective P450bufII. We demonstrate that P450bufI is unique in hydroxylating bufuralol in a cumene hydroperoxide (CuOOH) mediated reaction whereas P450bufII is active only in the classical NADPH- and O2-supported monooxygenation. In microsomes of liver biopsies of in vivo phenotyped poor metabolizers of debrisoquine or sparteine, the CuOOH-mediated activity was drastically reduced. Rabbit antibodies against a rat P-450 isozyme with high bufuralol 1'-hydroxylase activity (P450db1) precipitated exclusively P450bufI-type activity from solubilized microsomes. Western blotting of microsomes with these antibodies revealed a close correlation between the immunoreactive protein and CuOOH-mediated (+)-bufuralol 1'-hydroxylation. No immunoreactive protein was detected in liver microsomes of in vivo phenotyped poor metabolizers. These data provide evidence for a specific deficiency of P450bufI and are consistent with the complete or almost complete absence of this protein in the liver of poor metabolizers.
mesh_terms: D001555:Benzene Derivatives; D003577:Cytochrome P-450 Enzyme System / Q000172:deficiency* / Q000276:immunology / Q000378:metabolism; D003647:Debrisoquin / Q000378:metabolism*; D004983:Ethanolamines / Q000378:metabolism*; D006801:Humans; D006900:Hydroxylation; D007158:Immunologic Techniques; D007163:Immunosorbent Techniques; D007527:Isoenzymes / Q000378:metabolism; D007546:Isoquinolines / Q000378:metabolism*; D007700:Kinetics; D008862:Microsomes, Liver / Q000201:enzymology*; D009249:NADP / Q000378:metabolism; D011110:Polymorphism, Genetic; D013237:Stereoisomerism; D013379:Substrate Specificity
chemical_list: D001555:Benzene Derivatives; D004983:Ethanolamines; D007527:Isoenzymes; D007546:Isoquinolines; D009249:NADP; C010831:bufuralol; D003577:Cytochrome P-450 Enzyme System; C007164:cumene hydroperoxide; D003647:Debrisoquin