Dietary fat and 3-MC induction of hepatic nuclear and microsomal cytochrome P-450

Hepatic microsomes from male Holtzman albino rats fed a synthetic fat-free diet for 21 days had significantly less cytochrome P-450 and exhibited less binding capacity (delta Amax/mg protein) for aniline and octylamine than microsomes from similar rats fed a diet containing 10% corn oil. Treatment with 3-methylcholanthrene (3-MC) increased the concentrations of cytochrome P-450 (as measured by CO binding spectra) to nearly equal levels in both dietary groups, but the binding of aniline and octylamine to microsomes of rats fed the fat diet exceeded the increase in cytochrome P-450 concentration. Nuclear envelope concentrations of cytochrome P-450 were unaffected by diet. The administration of 3-MC to rats fed a fat-free diet failed to induce nuclear envelope P-450; however, in rats fed the corn oil diet, 3-MC increased this CO binding pigment over twofold. The affinity of nuclear envelope P-450 towards type II substrates was at least equal to that of microsomes, except in control rats fed the fat-free diet. In general, 3-MC pretreatment increased the binding affinity of nuclear envelop and microsomes toward aniline, while increasing affinity for SKF 525-A binding only to nuclear envelope. Molecular weight species in the region known to contain the cytochrome P-450 were quantified by fluorescence gel electrophoresis. Molecular weight species of 48,000 and 53,000 in the nuclear envelope had their counterparts in the microsomal preparation, but a 50,000 dalton component of nuclear envelope was not detected in microsomes. 3-Methylcholanthrene increased only a species with molecular weight 45,500 in the microsomal and nuclear envelope preparations. Rats fed the diet containing corn oil had microsomes with increased capacity for binding CO, but this was not accompanied by increased cytochrome P-450 protein concentration, as measured by quantitative fluorescence gel electrophoresis.