METABOLISM OF BENZENE HEXACHLORIDE ISOMERS AND RELATED COMPOUNDS IN VITRO. I. PROPERTIES AND DISTRIBUTION OF THE ENZYME.

Abstract

The in vitro metabolism of benzene hexachloride (BHC) isomers and related compounds was studied by using an enzyme from the house fly, Musca domestica L. The enzymatic reaction system essentially produced only watersoluble metabolites from 7-BHC (lindane). Metabolism was estimated by determining the substrate remaining in a reaction mixture, using a gas-liquid chromatograph equipped with an electron capture detector. The enzyme specifically required reduced glutathione for the reaction. The enzyme was found in the centrifugally prepared, soluble fraction of tissue homogenates, and its molecular weight was estimated to be approximately 54,000 by gel filtrations. The rates of metabolism of BHC isomers decreased in the order α > γ > δ; the β-isomer was nonreactive. The γ- and δ-1,3,4,5,6-pentachloro-1-cyclohexene (PCCH) isomers were metabolized much faster than the BHC isomers. Bromphenol blue had a very strong inhibitory effect on the enzymatic reaction. Other properties of the enzyme investigated included cofactor and substrate specificity, pH dependence, effect of temperature, stability, and reaction rates. The enzyme was partly purified by salting-out fractionation and gel filtration. No correlation was observed between the enzyme activity and resistance of the house fly to γ-BHC. A study of the distribution of the enzyme among 10 species of insects, the rat, and the rabbit showed that the house fly is outstandingly capable of metabolizing BHC and PCCH isomers.