大鼠肝脏葡萄糖-6-磷酸酶对D-葡萄糖磷酸化的异头特异性
Anomeric specificity of D-glucose phosphorylation by rat liver glucose-6-phosphatase.
作者信息
Ramirez R, Zähner D, Marynissen G, Sener A, Malaisse W J
机构信息
Laboratory of Experimental Medicine, Brussels Free University, Belgium.
出版信息
Biochem J. 1989 Jul 15;261(2):509-13. doi: 10.1042/bj2610509.
The anomeric specificity of D-glucose phosphorylation by hepatic glucose-6-phosphatase was examined in rat liver microsomes incubated in the presence of carbamoyl phosphate. At 10 degrees C, the Km for the equilibrated hexose and phosphate donor was close to 56 mM and 11 mM, respectively. The enzymic activity, which was increased in diabetic rats, was about 40% lower in untreated than in sonicated microsomes. No anomeric difference in affinity was found in sonicated microsomes. In untreated microsomes, however, the Km for beta-D-glucose was slightly lower than that for alpha-D-glucose. The maximal velocity was higher with beta- than alpha-D-glucose in both untreated and sonicated microsomes. These data indicate that the phosphotransferase activity of glucose-6-phosphatase cannot account for the higher rate of glycolysis and glycogen synthesis found in hepatocytes exposed to alpha- rather than beta-D-glucose.
在存在氨基甲酰磷酸的情况下孵育的大鼠肝微粒体中，研究了肝葡萄糖-6-磷酸酶对D-葡萄糖磷酸化的异头特异性。在10℃时，平衡己糖和磷酸供体的Km分别接近56 mM和11 mM。糖尿病大鼠的酶活性增加，未处理的微粒体中的酶活性比超声处理的微粒体低约40%。在超声处理的微粒体中未发现亲和力的异头差异。然而，在未处理的微粒体中，β-D-葡萄糖的Km略低于α-D-葡萄糖。在未处理和超声处理的微粒体中，β-D-葡萄糖的最大速度均高于α-D-葡萄糖。这些数据表明，葡萄糖-6-磷酸酶的磷酸转移酶活性不能解释在暴露于α-D-葡萄糖而非β-D-葡萄糖的肝细胞中发现的更高的糖酵解和糖原合成速率。
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