Effects of estradiol and nicotinamide adenine dinucleotide phosphate on rate of degradation of uterine glucose-6-phosphate dehydrogenase.

Direct measurement of the effects of e&radio1 on the rate of incorporation of “C-amino-acids into immunoprecipitable uterine glucose-6-P dehydrogenase (o-glucose-6-phosphate:NADP+ oxidoreductase, EC 1.1.1.49) indicates that the de nouo rate of synthesis of the enzyme is increased in ovariectomized mature rats in response to the hormone. The present study was undertaken to determine whether estradiol and the enzyme’s cofactor, NADP’, might affect the rate of degradation of the enzyme in the rat uterus. Total uterine proteins were pulse-labeled by intrauterine administration of [l-“Clglutamate to 12-h estradiol-treated ovariectomized mature rats at hourly intervals for 4 h. The clearance of [lJIC]glutamate from the uterine free amino acid pool was determined by an assay employing Escherichia coli glutamate decarboxylase. After metabolic clearance of the radioactive glutamate from the uterine free amino acid pool, the retention of the radioactivity in immunoprecipitable uterine glucose-6-P dehydrogenase was determined. Uterine glucose-6-P dehydrogenase is degraded with a t,,Z of >lOO h during the interval from 16 to 36 h after estradiol treatment. Coincident with the time at which total uterine glucose-6-P dehydrogenase activity begins to decrease, at the 36th h after the initial estradiol treatment, the enzyme begins to be degraded with a t,r2 of 24 h. A second injection of estradiol given during the period of decline in uterine enzyme activity results in complete inhibition of glucose-6-P dehydrogenase degradation for a period of up to 24 h. Intrauterine administration of NADP+ during the period of enzyme decline further increases the rate of uterine glucose-6-P dehydrogenase degradation. Thus, the “reinduction” of uterine glucose-6-P dehydrogenase synthesis by a second injection of estradiol is accompanied by a complete inhibition of intracellular depradation of uterine glucose-6-P dehydrogenase.