Evidence for the Common Identity of Glucose 6-Phosphatase, Inorganic Pyrophosphatase, and Pyrophosphate- Glucose Phosphotransferase

Abstract

The glucoseand inorganic pyrophosphate-dependent formation of glucose 6-phosphate has been demonstrated in mouse (1) and rat (2) liver mitochondrial preparations. The mouse mitochondrial enzyme catalyzing this reaction appears to be very closely related to an inorganic pyrophosphatasel activity found in such preparations (1). Recent studies2 have indicated that rat liver microsomes, which also contain an inorganic pyrophosphatase active at low pH (pH 4 to 6) (3, 4), are a considerably richer source of this phosphotransferase than are mitochondria. The common involvement of glucose 6-phosphate in the phosphotransferase and with another liver microsomal enzyme, glucose 6-phosphatase (5), as well as the acidic pH optima of both (4, 6), suggested that possibly the three enzymic activities might be interrelated. Interest in the problem was intensified by the finding that these activities could not be separated by repeated ammonium sulfate fractionations of deoxycholate-treated microsomes, and that all three activities were unstable to other fractionation procedures attempted. The results of investigations reported in this paper indicate that inorganic pyrophosphatase, pyrophosphate-glucose phosphotransferase, and glucose 6-phosphatase activities may be due to one, common enzyme.