Cobalt as a modifier of microsomal monooxgenases in mice
Legrum, W.; Stuehmeier, G.; Netter, K.J.
Toxicology and Applied Pharmacology 48(2): 195-204
1979
ISSN/ISBN: 0041-008X PMID: 573000 Document Number: 141644
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, this activity and that of ethoxyresorufin dealkylation is not changed. The deethylation of 7-ethoxycoumarin is even increased about 4-fold by Co pretreatment. The inhibitor metyrapone decreases the 7-ethoxycoumarin-deethylation more strongly in Co-pretreated animals than in controls. .alpha.-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 2 steps as manifested by 2 different inflection points of the inhibition curve that are apart from each other by 4 orders of magnitude in metyrapone concentration. Spectral measurements show a more pronounced binding spectrum of metyrapone in the Co-treated animals when the ligand is added in very low concentrations. No determination of ligand affinity was attempted. The described effects cannot be demonstrated after in vitro addition of cobaltous chloride to microsomes. Co administration to mice produces distinct and substrate-dependent alterations of the microsomal mixed function oxidase activity.