Yamashita H, Nakatani H, Tonomura B
Department of Food Science and Technology, Faculty of Agriculture, Kyoto University.
J Biochem. 1991 Oct;110(4):605-7. doi: 10.1093/oxfordjournals.jbchem.a123627.
Porcine pancreatic alpha-amylase (1,4-alpha-D-glucan glucanohydrolase) [EC 3.2.1.1] has both amylase activity (hydrolysis of alpha-1,4-D-glucoside bond of starch) and maltosidase activity (hydrolysis of p-nitrophenyl-alpha-D-maltoside to p-nitrophenol and maltose). By the modification of histidine residues of porcine pancreatic alpha-amylase with diethylpyrocarbonate (DEP), both amylase and maltosidase activities were decreased in the absence of chloride ion. In the presence of chloride ion, however, maltosidase activity of the modified enzyme was increased to more than 260% of that of the native enzyme, whereas amylase activity was decreased to less than 15% of the native enzyme. Since the chloride ion binding site is part of the active site loop [Buisson et al. (1987) Food Hydrocolloids 1,399-406 and Buisson et al. (1987) EMBO J. 6, 3909-3916], the special arrangements of both catalytic and modified histidine residues induced by the chloride ion binding would enhance only the maltosidase activity of the histidine-modified enzyme.
猪胰α-淀粉酶（1,4-α-D-葡聚糖葡聚糖水解酶）[EC 3.2.1.1]具有淀粉酶活性（水解淀粉的α-1,4-D-糖苷键）和麦芽糖酶活性（将对硝基苯基-α-D-麦芽糖苷水解为对硝基苯酚和麦芽糖）。用焦碳酸二乙酯（DEP）修饰猪胰α-淀粉酶的组氨酸残基后，在没有氯离子的情况下，淀粉酶和麦芽糖酶活性均降低。然而，在有氯离子存在的情况下，修饰酶的麦芽糖酶活性增加到天然酶的260%以上，而淀粉酶活性降低到天然酶的15%以下。由于氯离子结合位点是活性位点环的一部分[比松等人（1987年）《食品水胶体》1,399 - 406页和比松等人（1987年）《欧洲分子生物学组织杂志》6, 3909 - 3916页]，氯离子结合诱导的催化和修饰组氨酸残基的特殊排列只会增强组氨酸修饰酶的麦芽糖酶活性。
