The Mechanism of Glucose-6-phosphatase¹

Studies in Glycogen Storage Diseases. I. Intestinal Glucose-6-Phosphatase Activity in Patients with Von Gierke's Disease and Their Parents*

“…In view of the marked difference between the intestinal glucose-6-phosphatase activity in children as compared to adults, studies were done using guinea pigs of different ages (Table IV). The intestinal glucose-6-phosphatase activity was sig- Glucose has been reported to inhibit hepatic glucose-6-phosphatase activity but not nonspecific phosphatase (13). While the present work was in progress, Lea and Walker reported the same observation using intestinal mucosa obtained from the guinea pig (14).…”

“…The similarity between hepatic and intestinal glucose-6-phosphatase is further suggested by the fact that the latter enzyme is also inhibited by the addition of glucose (Table V). The kinetics of the glucose inhibition of glucose-6-phosphatase have been studied in detail by Hass and Byrne (13). The ability of glucose to similarly inhibit guinea pig intestinal glucose-6-phosphatase was recently reported by Lea and Walker, who also presented kinetic data supporting the con-1244 tention that the hepatic and intestinal enzyme activities were the same (14).…”

The glucose-6-phosphatase system

“…The observation that G6Pase catalyses an exchange reaction between glucose and Glc-6-P provided the first proof that this enzyme forms a phosphoenzyme intermediate [13], a mechanism that is also consistent with the multiple phosphotransferase activities. Incorporation of $#P into microsomal protein upon incubation with [$#P]Glc-6-P was demonstrated, and was shown to be inhibited by unlabelled Glc-6-P and by PP i , indicating that it is related to G6Pase [17,18].…”

“…Because of its reaction mechanism (Figure 1), which involves a phosphoenzyme intermediate [13] (see below), G6Pase also displays phosphotransferase activity, being able to synthesize Glc-6-P from glucose and various phosphate donors such as PP i , Man-6-P [11] and carbamoyl phosphate [14]. These activities are more apparent in microsomes treated with detergents [12].…”

Purification, characterization and initial rate kinetics of acyl-phosphate-hexose phosphotransferase from Aerobacter aerogenes

“…Glucose 6-phosphatase also catalyzes a hexose phosphate-hexose phosphotransferase reaction (Hass and Byrne, 1960;Segal, 1959). Notably, nucleoside polyphosphates and pyrophosphate are substrates for glucose 6-phos phatase (Nordlie, 1971), but not for acyl-phosphate-hexose phospho transferase (Bergmeyer and Moellering, 1965;Kamel and Anderson, 1967).…”