The fructose 6-phosphate site of phosphofructokinase. Epimeric specificity.
The fructose 6-phosphate site of phosphofructokinase. Epimeric specificity.
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磷酸果糖激酶的果糖 6-磷酸位点。
DOI：
10.1016/s0021-9258(17)33488-9
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发表时间：
1976
期刊：
影响因子：
--
通讯作者：
E. S. Younathan
中科院分区：
文献类型：
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作者：
T. Koerner;R. Voll;A. E. Ashour;E. S. Younathan
通过测试三种磷酸酮糖作为替代底物，研究了兔肌磷酸果糖激酶催化位点的差向异构体特异性。这些（及其差向异构碳）包括：D-阿洛酮糖-6-P（C-3）、D-塔格糖-6-P（C-4）和L-山梨糖-6-P（C-5）。米氏常数（和相对最大速度）分别为：3.0 mM（45%）、0.054 mM（104%）和11 mM（15%）。在相同条件下，D-果糖-6-P的Km为0.043 mM，任意Vmax为100%。该酶对D-阿洛酮糖-6-P的低亲和力表明C-3处的L构型是有效结合所需的，其特异性类似于其他几种果糖代谢酶。C-5的D构型对于底物的磷酸基团的紧密结合和正确取向也很重要。D-塔格糖-6-P与D-果糖-6-P的动力学常数在实验误差范围内一致。因此，C-4位的构型对活性不是必需的;这表明D-塔格糖可用于哺乳动物组织。报道了一种合成D-阿洛酮糖-6-P的新方法和一种改进的D-塔格糖-6-P的合成工艺。所有的产品和中间体的特征明确的化学和物理方法。
The epimeric specificity of the catalytic site of rabbit muscle phosphofructokinase was investigated by testing three ketose phosphates as alternate substrates. These (and their epimeric carbons) included: D-psicose-6-P (C-3), D-tagatose-6-P (C-4), and L-sorbose-6-P (C-5). The Michaelis constants (and relative maximal velocities) were: 3.0 mM (45%), 0.054 mM (104%), and 11 mM (15%), respectively. Under the same conditions, D-fructose-6-P had a Km of 0.043 mM and an arbitrary Vmax of 100%. The low affinity of the enzyme for D-psicose-6-P indicates that the L configuration at C-3 is required for effective binding, a specificity similar to several other fructose-metabolizing enzymes. The D configuration at C-5 is also important for tight binding and the proper orientation of the phosphate group of the substrate. The kinetic constants of D-tagatose-6-P were identical with those of D-fructose-6-P, within experimental error. Thus, the configuration at C-4 is not essential for activity; an indication that D-tagatose may be utilized in mammalian tissues. A novel method for the synthesis of D-psicose-6-P and an improved procedure for the synthesis of D-tagatose-6-P are described. All products and intermediates were characterized unequivocally by chemical and physical methods.