THE PH-DEPENDENCE OF THE ACTION PATTERN IN PORCINE PANCREATIC ALPHA-AMYLASE-CATALYZED REACTION FOR MALTOOLIGOSACCHARIDE SUBSTRATES
THE PH-DEPENDENCE OF THE ACTION PATTERN IN PORCINE PANCREATIC ALPHA-AMYLASE-CATALYZED REACTION FOR MALTOOLIGOSACCHARIDE SUBSTRATES
复制标题
DOI：
10.1016/0003-9861(91)90451-n
复制
发表时间：
1991-08-15
影响因子：
3.9
通讯作者：
NAKATANI, H
中科院分区：
文献类型：
--
作者：
ISHIKAWA, K;MATSUI, I;NAKATANI, H
猪胰腺α-淀粉酶（EC 3.2.1.1;缩写PPA）可水解淀粉和直链淀粉中的α-d-（1，4）糖苷键，对大多数底物而言，其最适pH值为6.9。然而，对于某些低分子底物的水解，最佳pH值变为5.2（石川，K.，例如，1990，Biochemistry 29，7119-7123）。以14 C标记的还原性末端葡萄糖为底物，研究了底物对PPA最适pH的影响。麦芽三糖的最适pH为5.2，而麦芽五糖和麦芽六糖在pH 6.9时不变。的pH值曲线的中间大小的基板麦芽四糖显示异常;的表观最佳pH值在5.5和6.5之间扩大和键断裂模式依赖于pH值，不同于其他基板检查。这些结果与缓冲系统或底物浓度无关。的麦芽寡糖的水解产物的分析表明，最佳pH值的转移到中性区域发生时，只有在生产性结合模式的PPA的第五个亚位点被占领的底物的葡萄糖残基。PPA的三催化残基模型是从一些改性麦芽低聚糖（对硝基苯基-α-d-麦芽糖苷、γ-环糊精、麦芽戊糖醇和麦芽六糖醇）的水解分析中推导出来的（石川，K.，例如，1990，Biochemistry 29，7119-7123）成功地适用于本工作中使用的直链麦芽寡糖。这些结果表明，线性寡糖底物的不同生产性结合方式直接影响PPA的催化能力和最佳pH。
Porcine pancreatic α-amylase (EC 3.2.1.1; abbreviated PPA), which hydrolyzes α-d-(1,4) glucosidic bonds in starch and amylose, displays an optimum at pH 6.9 for the majority of substrates. The optimum pH, however, shifted to 5.2 for the hydrolysis of some low molecular substrates (Ishikawa, K.,et al., 1990,Biochemistry29, 7119–7123). Details of the substrate-dependent shift of the optimum pH in PPA were studied by use of a series of maltooligosaccharides with14C-labeled reducing end glucose as substrates. The optimum pH for maltotriose was 5.2, whereas that for maltopentaose and maltohexaose was unchanged at pH 6.9. The pH profile for the intermediate size substrate maltotetraose showed abnormality; the apparent optimum pH was broadened between 5.5 and 6.5 and the bond cleavage pattern depended on pH, unlike that for the other substrates examined. These results were independent of either buffer systems or substrate concentration. Analyses of the hydrolysates of the maltooligosaccharides revealed that the shift of the optimum pH to the neutral region occurred only when the fifth subsite of PPA in the productive binding modes was occupied by a glucosyl residue of a substrate. The three-catalytic residue model of PPA deduced from the analysis of the hydrolysis of some modified maltooligosaccharides (p-nitrophenyl-α-d-maltoside, γ-cyclodextrin, maltopentaitol, and maltohexaitol) (Ishikawa, K.,et al., 1990,Biochemistry29, 7119–7123) was successfully adapted to the linear maltooligosaccharides used in this work. These results indicate that the different productive binding modes of the linear oligosaccharide substrates affect directly the catalytic power and the optimum pH of PPA.