NADPH-dependent and -independent loss of cytochrome P-450 in control and phenobarbital-induced rat hepatic microsomes incubated with carbon tetrachloride.

Carbon tetrachloride-mediated loss of cytochrome P-450 has been compared in hepatic microsomes from untreated and phenobarbital-treated rats. At concentrations of carbon tetrachloride greater than 2.5 mM, a direct effect (i.e., NADPH- independent) on cytochrome P-450 was observed. This apparently arose from the "solvent" properties of carbon tetrachloride as this effect could be duplicated with the physically similar alkyl halide 1,2-dibromo-3-chloropropane. NADPH-dependent loss of cytochrome P-450 occurred at lower concentrations with maximal response occurring at 2.5-5.0 mM. Residual cytochrome P-450 at these concentrations was similar in untreated and phenobarbital-treated microsomes. Mixed-function oxidase activities in phenobarbital-treated microsomes were reduced to levels below those of uninduced controls. The 52-kDa polypeptide(s) in untreated microsomes and that specifically induced in phenobarbital-treated microsomes were susceptible to NADPH-dependent carbon tetrachloride incubation. These data suggest that the susceptibility of specific forms of cytochrome P-450 to carbon tetrachloride can be duplicated in in vitro incubation. Furthermore, data on the direct action of carbon tetrachloride suggest that this route of damage must be taken into consideration when concentrations of carbon tetrachloride of 2.5 mM or greater are used in in vitro incubation systems.