The glucose-6-phosphatase system in rat hepatic microsomes displays hyperbolic kinetics at physiological glucose 6-phosphate concentrations.
The kinetics of rat liver glucose-6-phosphatase (EC 3.1.3.9) were studied in intact and detergent-disrupted microsomes from normal and diabetic rats at pH 7.0 using two buffer systems (50 mM Tris-cacodylate and 50 mM 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid) and glucose-6-P varied from 20 microM to 10 mM. Identical data were obtained when the phosphohydrolase activity was quantified by a colorimetric determination of Pi or by measuring 32Pi formed during incubations with [32P]glucose-6-P. In every instance the initial rate data displayed excellent concordance with that expected for a reaction obeying Michaelis-Menten kinetics. The present findings agree with recently reported results of Traxinger and Nordlie (Traxinger, R. R., and Nordlie, R. C. 1987) J. Biol. Chem. 262, 10015-10019) that glucose-6-phosphatase activity in intact microsomes exhibits hyperbolic kinetics at concentrations of glucose-6-P above 133 microM, but fail to confirm their finding of sigmoid kinetics at substrate concentrations below 133 microM. We conclude that glucose-6-P hydrolysis conforms to a hyperbolic function at concentrations of glucose-6-P existing in livers of normal and diabetic rats in vivo.
Canfield
W K
WK
Division of Nutritional Sciences, Cornell University, Ithaca, New York 14853.
Arion
W J
WJ
D000818:Animals; D005952:Glucose-6-Phosphatase / Q000378:metabolism*; D019298:Glucose-6-Phosphate; D005958:Glucosephosphates / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D051381:Rats; D011919:Rats, Inbred Strains
D005958:Glucosephosphates; D019298:Glucose-6-Phosphate; D005952:Glucose-6-Phosphatase