Cross specificity in some vertebrate and insect glutathione-transferases with methyl parathion (dimethyl p-nitrophenyl phosphorothionate), 1-chloro-2,4-dinitro-benzene and s-crotonyl-N-acetylcysteamine as substrates

Biodegradation of alpha-hexachlorocyclohexane. VII. Resolution, purification, and characterization of an alpha-HCH dechlorinating enzyme from rat liver cytosol

From rat liver cytosol, an enzyme was isolated which catalyzes the dechlorination of alpha-, gamma-, and delta-HCH. The enzyme also catalyzes the conjugation of GSH with 1,2-dichloro-4-nitrobenzene, and with 1 -chloro-2,4-dinitrobenzene. The enzyme has a molecular weight of about 46000 and its molecule is composed of two subunits of similar size. The optimum for the dechlorination of alpha-HCH lies at pH 8.0. The Michaelis constant is 0.12 mM for alpha-HCH (with 1 mM GSH as constant substrate), and maximal velocity was determined to be 0.25 moles Cl- -min -1 per mole enzyme.

Drug induction of hepatic glutathione S-transferases in male and female rats*

The induction of the glutathione S-transferases by phenobarbital and polycyclic hydrocarbons was studied in male and female rats. Administration of phenobarbital resulted in 60-80% increase in S-aryl and S-aralkyl enzyme specific activities, whereas the S-epoxide and S-alkyl activities were increased by 30-40%. In following the sequence of induction, the former two activities were noted to reach peak activities before an increase in the latter two activities was observed. Both 3-methylcholanthrene and 3,4-benzopyrene were shown toi nduce these four enzymic activities, although without the discrimination between pairs of activities noted with phenobarbital. No change in Km accompanied the increase in Vmax. after induction by drugs, and no change occurred in Ki for sulphobromophthalein inhibition. Significantly lower enzyme specific activities were found for three of the activities studied in female rats but no difference was observed in the S-alkyltransferase activity. However, the proportional increase in the enzymic activities in response to phenobarbital was the same in males and females. These studies demonstrate the drug induction of a group of cytosolic drug-metabolizing enzymes as well as the identification of sex differences in these activities.