嗜热脂肪芽孢杆菌嗜热葡萄糖激酶的初速率研究。
Initial-rate studies of a thermophilic glucokinase from Bacillus stearothermophilus.
作者信息
Ishikawa H, Maeda T, Hikita H
机构信息
Department of Chemical Engineering, University of Osaka Prefecture, Japan.
出版信息
Biochem J. 1987 Nov 15;248(1):13-20. doi: 10.1042/bj2480013.
The initial rates of phosphorylation of glucose catalysed by glucokinase from Bacillus stearothermophilus were measured over a wide range of glucose, MgATP2-, MgADP- and glucose 6-phosphate concentrations. The results of the effects of the inhibitors on the initial rates suggest that the reaction mechanism is essentially the ordered Bi Bi, in which glucose adds to the enzyme before MgATP2- and glucose 6-phosphate is released from the enzyme after the dissociation of MgADP-, and also suggest that the final step in which glucose 6-phosphate is released is irreversible. For many reaction schemes, the rate equations were derived on the basis of the pseudo-steady-state assumption and were used to correlate the experimental rate data. From this result, we concluded that the reaction obeys the ordered mechanism accompanied by the formation of a non-productive ternary complex, glucose-MgADP--enzyme. By using the experimental Dalziel coefficients phi i, some kinetic parameters were evaluated. The enzyme was characterized by the thermal stability and the low Michaelis constant, the values of which were 54 microM for glucose and 32 microM for MgATP2-.
在广泛的葡萄糖、MgATP²⁻、MgADP⁻和6-磷酸葡萄糖浓度范围内，测定了嗜热脂肪芽孢杆菌葡萄糖激酶催化葡萄糖磷酸化的初始速率。抑制剂对初始速率影响的结果表明，反应机制本质上是有序的双底物双产物机制，即葡萄糖在MgATP²⁻之前与酶结合，MgADP⁻解离后6-磷酸葡萄糖从酶上释放，并且还表明6-磷酸葡萄糖释放的最后一步是不可逆的。对于许多反应方案，基于伪稳态假设推导了速率方程，并用于关联实验速率数据。根据这个结果，我们得出结论，该反应遵循有序机制，伴随着非生产性三元复合物葡萄糖-MgADP⁻-酶的形成。通过使用实验性的达尔齐尔系数φi，评估了一些动力学参数。该酶具有热稳定性和低米氏常数的特点，其值分别为葡萄糖54μM和MgATP²⁻32μM。
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