Biological Regulation of Inorganic Pyrophosphate-Glucose Phosphotransferase and Glucose 6-Phosphatase

Previous studies (4) on the effects of glucocorticoid therapy on liver microsomal glucose 6-phosphate phosphohydrolase (EC 3.1.3.9) and associated inorganic pyrophosphate-glucose phosphotransferase activity have been extended to include investigations of the effects, in vivo, of the synthetic steroid triamcinolone when administered to animals in which protein biosynthesis had been blocked by treatment with actinomycin D. Actinomycin (10 µg/100 g of body weight) was administered daily for 3 days by intraperitoneal injection to a group of 11 rats. Triamcinolone (1.0 mg/100 g of body weight) was injected daily ½ hour later into five of these animals. Enzymic activities were assayed in fresh liver homogenates which were supplemented either with 0.1 part of 2% sodium deoxycholate solution or with an equal volume of distilled water. Glucose 6-phosphate phosphohydrolase and pyrophosphate-glucose phosphotransferase activity levels increased, respectively, to 139% and 177% of comparable values for activities in animals receiving actinomycin only, based on assays carried out in the absence of detergent. However, statistically significant differences in corresponding activity values for the two groups of animals disappeared when assays were carried out with detergent-supplemented homogenates. These findings constitute additional evidence supporting our earlier suggestion (4) that the principal effect of glucocorticoid therapy on the various activities of microsomal glucose 6-phosphatase is that of activation of preexisting enzyme; furthermore, they indicate that this process is independent of protein biosynthesis.