Activation of carbon tetrachloride, and distribution of NADPH-cytochrome c reductase, cytochrome P-450, and other microsomal enzyme activities in rat tissue

Abstract

Activities of various components of microsomal suspensions obtained from a considerable number of rat tissues have been studied. The tissue contents reported include NAD(P)H-cytochrome c reductases, NAD(P)H-ferricyanide reductases, cytochrome b 5 and P-450, lipid peroxidation and covalent binding of 14CCl 4. The reductase activities were found to be widely distributed, and NADH-liinked activities were generally much higher than the corresponding NADPH-dependent activities. NADPH-cytochrome c reductase was most active in liver, adrenal and small intestinal mucosa. Cytochrome b 5 was also present in most tissues in easily detectable amounts, but the content of cytochrome P-450 was very low in most tissues with the exception of liver, adrenal and kidney. Values for cytochrome P-450 in lung, spleen, brain, testis, lactating mammary gland are also reported. NADPH-ADP/Fe 2+-linked lipid peroxidation showed a rather similar distribution to cytochrome P-450, being most active in liver with very low activities in tissues like lung and spleen. CCl 4-stimulated lipid peroxidation was detectable in liver and kidney but not in other tissues to any significant extent; spin trapping of the trichloromethyl free radical and covalent binding from 14CCl 4 was mainly associated with liver microsomes, with less than 5% activity relative to liver being observed in other tissues. The very low rate of lipid peroxidation in extrahepatic microsomes is discussed in terms of the fatty acid contents of the suspensions, and of antioxidant status. The activation of CCl 4 by the NADPH-cytochrome P-450 chain does not appear to be a simple function of the activities of the NADPH-flavoprotein, cytochrome P-450, or relative content of polyunsaturated fatty acids.