Cobalt as a modifier of microsomal monooxygenases in mice

Abstract

The influence of cobaltous chloride treatment on various functions of microsomal cytochromes was studied in C57BL 6J Han mice. Two daily doses of 40 mg/kg reduce the cytochrome P-450 content and the ethylmorphine N-demethylase activity to about 60%, based on microsomal protein. On the basis of microsomal cytochrome content, however, this activity and that of ethoxyresorufin dealkylation is not changed. In contrast, the deethylation of 7-ethoxycoumarin is even increased about fourfold by cobalt pretreatment. The inhibitor metyrapone decreases the 7-ethoxycoumarin-deethylation more strongly in cobalt-pretreated animals than in controls. α-Naphthoflavone has the opposite effect. The use of these “diagnostic” inhibitors suggests a certain prevalence of cytochrome P-450-like material in the microsomes. When ethoxyresorufin is the substrate, metyrapone inhibits the reaction apparently in two steps as manifested by two different inflection points of the inhibition curve that are apart from each other by four orders of magnitude in metyrapone concentration. Spectral measurements show a more pronounced binding spectrum of metyrapone in the cobalt-treated animals when the ligand is added in very low concentrations. However, no determination of ligand affinity was attempted. The described effects cannot be demonstrated after in vitro addition of cobaltous chloride to microsomes. The results suggest that cobalt administration to mice produces distinct and substrate-dependent alterations of the microsomal mixed function oxidase activity.