果糖是大鼠肝脏“葡萄糖激酶”（己糖激酶D）的良好底物。
Fructose is a good substrate for rat liver 'glucokinase' (hexokinase D).
作者信息
Cárdenas M L, Rabajille E, Niemeyer H
出版信息
Biochem J. 1984 Sep 1;222(2):363-70. doi: 10.1042/bj2220363.
Rat liver 'glucokinase' (hexokinase D) catalyses the phosphorylation of fructose with a maximal velocity about 2.5-fold higher than that for the phosphorylation of glucose. The saturation function is hyperbolic and the half-saturation concentration is about 300 mM. Fructose is a competitive inhibitor of the phosphorylation of glucose with a Ki of 107 mM. Fructose protects hexokinase D against inactivation by 5,5'-dithiobis-(2-nitrobenzoic acid), and the apparent dissociation constants are about 300 mM in the presence of different concentrations of the inhibitor. The co-operativity of the enzyme in the phosphorylation of glucose can be abolished by addition of fructose to the reaction medium. Fructose appears to be no better as a substrate for the other mammalian hexokinases than it is for hexokinase D. It is proposed that the name 'glucokinase' ought to be reserved for enzymes that are truly specific for glucose, such as those of micro-organisms and invertebrates, and that liver glucokinase must be called hexokinase D (or hexokinase IV) within the classification EC 2.7.1.1.
大鼠肝脏“葡萄糖激酶”（己糖激酶D）催化果糖磷酸化的最大速度比催化葡萄糖磷酸化的最大速度高约2.5倍。饱和函数呈双曲线，半饱和浓度约为300 mM。果糖是葡萄糖磷酸化的竞争性抑制剂，其抑制常数（Ki）为107 mM。果糖可保护己糖激酶D不被5,5'-二硫代双（2-硝基苯甲酸）灭活，在不同浓度抑制剂存在下，表观解离常数约为300 mM。向反应介质中添加果糖可消除该酶在葡萄糖磷酸化过程中的协同性。果糖作为其他哺乳动物己糖激酶的底物，并不比作为己糖激酶D的底物表现更好。有人提出，“葡萄糖激酶”这个名称应保留给真正对葡萄糖具有特异性的酶，如微生物和无脊椎动物的那些酶，并且在EC 2.7.1.1分类中，肝脏葡萄糖激酶必须称为己糖激酶D（或己糖激酶IV）。
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