Metabolic activation of carbon tetrachloride: induction of cytochrome P-450 with phenobarbital or 3-methylcholanthrene and its effect on covalent binding.
Anaerobic incubation of [14C]carbon tetrachloride with normal rat liver microsomes and microsomes from rats treated with the inducers phenobarbital (PB) and 3-methylcholanthrene (MC) reveals distinct differences in metabolic activation. While the increase in CO-binding pigment is comparable for both inducers, metabolism of CC14 is enhanced only by PB-induction; MC-induced microsomes are equivalent to microsomes from untreated animals. Sodium dodecyl sulphate (SDS)-electrophoresis of microsomal proteins confirms the expected increase at 52 000 daltons (cytochrome P-450 PB) on PB-induction, at 56 000 daltons (cytochrome P-450MC) on MC-induction; after anaerobic incubation with [14C]CC14 the electrophoretic pattern is largely unchange. The highly reactive radical intermediates of CC14-metabolism should attack the closest possible partner. Most of protein-bound radioactivity is located in the mass range between 47 000 and 54 000 daltons, indicating that cytochrome P-450PB is the isoenzyme mainly responsible for CC14-activation; cytochrome P-450MC plays virtually no role in metabolic activation. The direct participation of NADPH-cytochrome P-450 reductase appears unlikely, since the specific binding to proteins in the corresponding mass range is not elevated. A significant percentage of label is attached to proteins at 120 000 daltons and above, presumably oligomers of cytochrome P-450 apoprotein.
D000693:Anaerobiosis; D000818:Animals; D001711:Biotransformation; D002251:Carbon Tetrachloride / Q000378:metabolism*; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis*; D004790:Enzyme Induction / Q000187:drug effects; D066298:In Vitro Techniques; D008297:Male; D008748:Methylcholanthrene / Q000494:pharmacology; D008862:Microsomes, Liver / Q000201:enzymology; D010634:Phenobarbital / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains
D008748:Methylcholanthrene; D003577:Cytochrome P-450 Enzyme System; D002251:Carbon Tetrachloride; D010634:Phenobarbital