title: Studies on the interactions between phospholipids and membrane-bound enzymes in microsomes. Effects of phospholipases C on kinetic properties of the glucose-6-phosphatase system in rat liver microsomes.
abstract: 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 phosphatidylethanolamine 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 phosphotransferase was decreased. When phosphatidylinositol was hydrolyzed by phosphatidylinositol-specific phospholipase C of B. thuringiensis, the activities of phosphohydrolase and phosphotransferase 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 10 mM. However, at a concentration lower than 1 mM, the activity of phosphohydrolase 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 phosphatidylinositol 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 phosphatidylinositol.
mesh_terms: D000818:Animals; D017920:Antiporters; D003016:Clostridium perfringens / Q000201:enzymology; D005952:Glucose-6-Phosphatase / Q000378:metabolism*; D007425:Intracellular Membranes / Q000502:physiology; D007700:Kinetics; D008297:Male; D008563:Membrane Lipids / Q000502:physiology*; D008862:Microsomes, Liver / Q000201:enzymology*; D009004:Monosaccharide Transport Proteins; D010716:Phosphatidylinositols; D010740:Phospholipases / Q000494:pharmacology*; D010743:Phospholipids / Q000502:physiology*; D010770:Phosphotransferases / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D013379:Substrate Specificity; D010738:Type C Phospholipases / Q000378:metabolism / Q000494:pharmacology*
chemical_list: D017920:Antiporters; D008563:Membrane Lipids; D009004:Monosaccharide Transport Proteins; D010716:Phosphatidylinositols; D010743:Phospholipids; C503533:Slc37a4 protein, rat; C111261:glucose 6-phosphate(transporter); D010770:Phosphotransferases; D010740:Phospholipases; D005952:Glucose-6-Phosphatase; D010738:Type C Phospholipases