Maximum activities and properties of glucose 6-phosphatase in muscles from vertebrates and invertebrates.
1. The maximum catalytic activities of glucose 6-phosphatase were measured in a large number of muscles from vertebrates and invertebrates. The activities range from less than 0.1 to 8.0 mumol/min per g fresh wt. at 30 degrees C: the highest activity, observed in the flight muscle of the wasp (Vespa vulgaris), is similar to that in rat liver. The hydrolytic activity was shown to be specific towards glucose 6-phosphate. 2. The pH optimum was 6.8 and the Km was approx. 0.6 mM (flight muscle of a moth). 3. Almost all of the glucose 6-phosphatase activity from extracts of the flight muscle of a moth and the pectoral muscle of a pigeon were recovered in the cytosolic fraction (i.e. 150,000 g supernatant). 4. During development of the locust (Schistocerca gregaria), the activity of the phosphatase in the flight muscle increased during the first 3 days after the final moult. 5. The activity of glucose 6-phosphatase from insect and avian muscle was separated from that of non-specific phosphatase on a Bio-Gel P-100 column. 6. For the activities from 63 muscles, there was a strong positive correlation between those of glucose 6-phosphatase and hexokinase, but no correlation between the activities of glucose 6-phosphatase and fructose bisphosphatase. It is suggested that the role of glucose 6-phosphate in muscle is either to produce glucose from glucose 6-phosphate derived from glycogen or to provide the enzymic basis for a substrate ("futile") cycle between glucose and glucose 6-phosphatase in muscle to improve the sensitivity of the mechanism that regulates the rate of glucose phosphorylation.
D000818:Animals; D005426:Flight, Animal; D006597:Fructose-Bisphosphatase / Q000378:metabolism; D005952:Glucose-6-Phosphatase / Q000378:metabolism*; D006593:Hexokinase / Q000378:metabolism; D066298:In Vitro Techniques; D007313:Insecta / Q000201:enzymology; D007448:Invertebrates / Q000378:metabolism; D007700:Kinetics; D051379:Mice; D009132:Muscles / Q000201:enzymology*; D009206:Myocardium / Q000201:enzymology; D011817:Rabbits; D051381:Rats; D013045:Species Specificity; D014714:Vertebrates / Q000378:metabolism
D006593:Hexokinase; D006597:Fructose-Bisphosphatase; D005952:Glucose-6-Phosphatase