Molecular basis of the effects of chloride ion on the acid-base catalyst in the mechanism of pancreatic α-amylase
Molecular basis of the effects of chloride ion on the acid-base catalyst in the mechanism of pancreatic α-amylase
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DOI：
10.1021/bi048201t
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发表时间：
2005-03-08
期刊：
影响因子：
2.9
通讯作者：
Nahoum, V
中科院分区：
文献类型：
--
作者：
Qian, MX;Ajandouz, E;Nahoum, V
猪胰腺α -淀粉酶（PPA）是α -淀粉酶家族的一种酶，参与淀粉的降解。像这个家族的其他成员一样，PPA需要氯化物达到最大的活性水平。为了进一步解释氯离子活化的机理，用x射线晶体学分析了野生型PPA与麦芽糖糖用无氯缓冲液浸泡的晶体。发现酸/碱催化剂Glu233残基发生了明显的重定向。结构结果和动力学数据表明，由于氯离子的存在，酸/碱催化剂保持在活性位点的最佳位置，指向可剪切键原子。因此，本研究解释了氯离子活化PPA的机理。
Pig pancreatic alpha-amylase (PPA), an enzyme belonging to the alpha-amylase family, is involved in the degradation of starch. Like some other members of this family, PPA requires chloride to reach maximum activity levels. To further explain the mechanism of chloride activation, a crystal of wild-type PPA soaked with maltopentaose using a chloride-free buffer was analyzed by X-ray crystallography. A conspicuous reorientation of the acid/base catalyst Glu233 residue was found to occur. The structural results, along with kinetic data, show that the acid/base catalyst is maintained in the active site, in an optimum position, pointing toward the scissile bond-atom, due to the presence of chloride ions. The present study therefore explains the mechanism of PPA activation by chloride ions.