Cytochrome P-450 induction by clofibrate

Hypolipidaemic drugs induce peroxisomal proliferation in the liver and many induce the formation of the hepatic endoplasmic reticulum in general and the formation of cytochrome P-450 in particular. We have induced the formation of rat liver microsomal cytochrome P-450 by the administration of the hypolipidaemic drug clofibrate, isolated the endoplasmic reticulum, solubilized the cytochrome P-450 from these membranes and subdivided the cytochrome P-450 into four fractions by the use of hydrophobic, anionic, cationic and adsorption chromatography. One of these fractions (cytochrome P-450 fraction 1) was highly purified to a specific content of 17nmol of cytochrome P-450/mg of protein and the protein was active in a reconstituted enzyme system towards the 12and 1-hydroxylation of the fatty acid, dodecanoic (lauric) acid, with preferential activity towards the 12-hydroxy metabolite. This reconstituted activity was absolutely dependent on NADPH, NADPH-cytochrome P-450 reductase and cytochrome P-450, indicating the role of the mixed-function oxidase system in the metabolism of lauric acid. Another fraction of the haemoprotein (cytochrome P-450 fraction 2) preferentially formed 1 1-hydroxylauric acid, whereas a third fraction (cytochrome P-450 fraction 3) exhibited only trace laurate oxidase activity and was similar to the phenobarbitone form of the haemoprotein in that these last two cytochromes rapidly turned-over the drug benzphetamine. The molecular weights and spectral properties of these cytochrome P-450 fractions are reported, along with the phenobarbitone-induced form of the enzyme and the nature of the cytochrome(s) induced by clofibrate pretreatment are discussed in the terms of possible haemoprotein heterogeneity.