1983 Volume 93 Issue 2 Pages 537-546
Through kinetic analysis, the relationships between the glucose-6-phosphatase system and constituent phospholipids were studied in rat liver microsomes.
When phosphoglycerides such as phosphatidylcholine and phosphatidylethanol-amine on the microsomal membrane were hydrolyzed by phospholipase C of C. perfringens, the activities of glucose-6-P phosphohydrolase and glucose-6-P:glucose phosphotransferase both decreased with or without subsequent exposure to taurocholate. In these cases, the Michaelis constants (Km) for glucose-6-P were increased, concomitant with the decrease in the maximal velocities (Vmax) for glucose-6-P hydrolysis. On exposure to taurocholate, the apparent Km for glucose of phos-photransferase was decreased.
When phosphatidylinositol was hydrolyzed by phosphatidylinositol-specific phospholipase C of B. thuringiensis, the activities of phosphohydrolase and phos-photransferase were both decreased on exposure to taurocholate. In this case, the value of Vmax of phosphohydrolase was decreased and that of Km for glucose-6-P was slightly decreased, while the apparent Km for glucose of phosphotransferase was increased. Without exposure to detergent, the activities of phosphohydrolase and phosphotransferase both decreased at glucose-6-P concentrations higher than 10mM. However, at a concentration lower than I mm, the activity of phospho-hydrolase became higher than that of the control, and Vmax and Km for glucose-6-P were decreased.
A similar tendency was also observed in microsomes where membranous phos-phatidylinositol was hydrolyzed, when they were treated with DIDS (an anion-transport inhibitor).
From these results, it is concluded that the activity of glucose-6-phosphatase is greatly influenced by changes of the phospholipids on the microsomal membrane, and the activity of glucose-6-P translocase is stimulated by the breakdown of phos-phatidylinositol.
