Involvement of diminution of glutathione, produced by deficiency of methionine in the diet, in the elevation of malic enzyme level in rat liver

Abstract

Rats fed on a low protein diet show an increase in the specific activity of malic enzyme and a concomitant decrease of glutathione concentration. We have studied the effect on malic enzyme activity of supplementing of low protein diet with essential amino acids. Only when methionine was excluded from the diet did the specific activity of malic enzyme increase to the same extent as found in rats fed with low protein diet. Immunoprecipitation of malic enzyme indicated that specific activity changes are the result of changes in the amounts of enzyme. Under all dietary conditions studied, the increase in malic enzyme activity is associated with a decrease in the concentration of GSH. To evaluate the possible causative role of GSH in malic enzyme induction, the specific activity of malic enzyme was measured in rats treated with BSO, an inhibitor of GSH biosynthesis. The reuslts show that in BSO-treated rats the decrease of GSH levels is also accompanied by an increase in the activity of malic enzyme.