Liver Microsomal Glucose 6-Phosphatase, Inorganic Pyrophosphatase, and Pyrophosphate-Glucose Phosphotransferase

Abstract

Recently, we (1) showed that inorganic pyrophosphate-glucose phosphotmnsferase activity (Equation l), which originally was discovered by Rafter [2), resides in microsomes of rat liver and appears to be identical with glucose 6-phosphatase.Studies with freshly prepared microsomes in which various nucleoside triphosphates were employed as potential phosphoryl group donors in place of inorganic pyrophosphate resulted in very little glucose g-phosphate production.However, it was found that treatment of microsomes with deoxycholate produced a marked activation of nucleoside triphosphate-and diphosphate-glucose phosphotransferasel activities (Equations 2 and 3).PPi + glucose + glucose-6-P + Pi (1)Nucleoside 5'-triphosphate + glucose + glucose-6-P + nucleoside 5'-diphosphate(2)Nucleoside 5'-diphosphate + glucose + glucose-6-P + nucleoside 5'.monophosphate (3) Characterization of these activities as to tissue distribution, substrate specificity, pH optima, and other catalytic properties, and responses to alloxan diabetes and insulin administration are described in this paper.,4 comparison of many properties of these activities with pyrophosphate-glucose phosphotransferase is made.A physiological role for these transferases in the diabetic animal is suggested.EXPERIMENTAL PROCEDURE Sources of materials were as described previously (1,3), except that; the glucose-6-P dehydrogenase employed was a product of C. F.