Canfield W K, Arion W J
Division of Nutritional Sciences, Cornell University, Ithaca, New York 14853.
J Biol Chem. 1988 Jun 5;263(16):7458-60.
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.
在pH 7.0条件下，使用两种缓冲系统（50 mM三羟甲基氨基甲烷 - 二甲胂酸盐和50 mM 4 -（2 - 羟乙基）-1 - 哌嗪乙磺酸），研究了正常和糖尿病大鼠完整及经去污剂破坏的微粒体中大鼠肝脏葡萄糖 - 6 - 磷酸酶（EC 3.1.3.9）的动力学，葡萄糖 - 6 - 磷酸（glucose - 6 - P）浓度范围为20 μM至10 mM。当通过比色法测定无机磷酸（Pi）或测量与[32P]葡萄糖 - 6 - P孵育过程中形成的32Pi来定量磷酸水解酶活性时，获得了相同的数据。在每种情况下，初始速率数据与符合米氏动力学反应预期的数据显示出极好的一致性。本研究结果与Traxinger和Nordlie最近报道的结果（Traxinger, R. R., and Nordlie, R. C. 1987）J. Biol. Chem. 262, 10015 - 10019）一致，即在完整微粒体中，当葡萄糖 - 6 - P浓度高于133 μM时，葡萄糖 - 6 - 磷酸酶活性呈现双曲线动力学，但未能证实他们在底物浓度低于133 μM时发现的S形动力学。我们得出结论，在正常和糖尿病大鼠体内肝脏中存在的葡萄糖 - 6 - P浓度下，葡萄糖 - 6 - P水解符合双曲线函数。
