人血清脱金属铁传递蛋白裂解焦磷酸键的研究(英文)

The cleavage of pyrophosphate by human serum apo-transferrin

目的：测定人血清脱金属铁传递蛋白裂解焦磷酸键的反应速率常数。方法：应用^31P NMR技术，在不同pH值及不同浓度MgCl2存在条件下．测定了脱金属铁传递蛋白与焦磷酸二钠反应的核磁共振图谱，根据焦磷酸盐的摩尔浓度（对应于其谱峰强度）随时间的变化情况，应用动力学公式对数据进行拟合。结果：当人血清脱金属铁传递蛋白（0．5～1.0mmol／L）与焦磷酸盐的反应孽尔浓度比为1：5时．在312K条件下，反应速率常数分别为：8．83×10^-1L·mmol^-1·h^-1（pH6．85）、9.59×10^-1L·mmol^-1·h^-1（PH7．40）和1．38×10^-3L·mmol^-1·h^-1（PH8．15）。在2mmol／L MgCl2存在时，pH7．40、312K条件下，反应速率常数为1．21×10^-3L·mmol^-1·h^-1。结论：人血清脱金属铁传递蛋白能缓慢地将焦磷酸根裂解为磷酸根，反应具有二级反应动力学性质．Mg^2＋对该裂解反应有弱催化作用。

Objective： To determine the rate constants for the cleavage of pyrophosphate to phosphate by human serum apotransferrin. Methods.. The cleavage was followed by ^31 P NMR spectroscopy. The data for concentration changes of pyrophosphate （as determined from its NMR peak intensity） with time,in the absence and the presence of MgCl4 ,at different pH values,were fitted to give second order rate constants. Results.. The rate constants at 312 K were 8.83 ×10^-1L·mmol^-1·h^-1 at pH 6.85, 9.59×10^-1L·mmol^-1·h^-1 at pH 7.4,and 1.38×10^-3L·mmol^-1·h^-1 at pH 8.15,for reactions of apo-transferrin （0.5- 1.0 retool/L） with 5 molar equivalence of pyrophosphate. The rate constant increased to 1.21 ×10^-3L·mmol^-1·h^-1 at pH 7.4,312 K when 2 mmol/L. MgCl2 was added. Conclusion： The cleavage of pyrophosphate to phosphate by human serum apotransferrin is very slow and follows the second-order kinetics. Mg^2＋ can slightly enhance the rate of the cleavage.