MULTIPLICITY OF CYTOCHROMES P-450 DURING DEVELOPMENT

Abstract

Drug oxidations are catalyzed by the cytochromes P-450 monooxygenase complex. Livers of induced adult animals possess multiple forms of the hemoprotein component (P-450s) with distinct substrate and product specificities (Mol. Pharmacol., 11:874, 1975). Prompted by (1) a difference in neonatal pharmacokinetic profiles between caffeine and theophylline and most other ‘oxidized’ drugs (phenytoin, etc.) and (2) a reported difference in the substrate specificity of human fetal and adult hepatic monooxygenase activity, we are assessing individual P-450s in untreated and developing organisms. Hepatic microsomes from adult or 72-hr guinea pigs are treated for 3 hrs at 23° in a buffer containing glycerol, cholate, and Emulgen 911, a nonionic detergent. The solubilized P-450s, measured by CO binding, have mol. wts. of ca. 50,000 upon gel filtration. These P-450s can be separated from other hemoproteins and resolved into 4 peaks by DE52 chromatography with ca. 50% recovery. Each peak, when isoelectrically focused in poly-acrylamide gels, can be further resolved into multiple protein bands, 2-4 of which stain for heme. Mixing experiments support this multiplicity. Similar results are obtained with adult rat liver microsomes. Guinea pigs, which exhibit substantial increases in hepatic monooxygenase activity within 72 hrs of birth also exhibit at this time multiple forms of P-450s as assessed by the above methods. Comparisons of gels and elution patterns of adult and 72 hr solubilized P-450s suggest that the relative proportions of multiple forms vary during development.