Freer S N
Fermentation Biochemistry Research Unit, U.S. Department of Agriculture, Peoria, Illinois 61604.
Appl Environ Microbiol. 1993 May;59(5):1398-402. doi: 10.1128/aem.59.5.1398-1402.1993.
The extracellular alpha-amylase (1,4-alpha-D-glucanglucanohydrolase; EC 3.2.1.1) from maltose-grown Streptococcus bovis JB1 was purified to apparent homogeneity by ion-exchange chromatography (Mono Q). The enzyme had an isoelectric point of 4.50 and an apparent molecular mass of 77,000 Da, as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The enzyme was rich in acidic and hydrophobic amino acids. The 15-amino-acid NH2-terminal sequence was 40% homologous with the Bacillus subtilis saccharifying alpha-amylase and 27% homologous with the Clostridium acetobutylicum alpha-amylase. alpha-Amylase activity on soluble starch was optimal at pH 5.0 to 6.0. The enzyme was relatively stable between pH 5.5 and 8.5 and at temperatures below 50 degrees C. When soluble potato starch was used as the substrate, the enzyme had a Km of 0.88 mg.ml-1 and a kcat of 2,510 mumol of reducing sugar.min-1.mg of protein-1. The enzyme exhibited neither pullulanase nor dextranase activity and was 40 to 70% as active on amylopectin as on amylose. The major end products of amylose hydrolysis were maltose, maltotriose, and maltotetraose.
从以麦芽糖为生长底物的牛链球菌JB1中提取的胞外α-淀粉酶（1,4-α-D-葡聚糖葡聚糖水解酶；EC 3.2.1.1），通过离子交换色谱法（Mono Q）纯化至表观均一。经十二烷基硫酸钠-聚丙烯酰胺凝胶电泳估计，该酶的等电点为4.50，表观分子量为77,000 Da。该酶富含酸性和疏水氨基酸。其15个氨基酸的NH2末端序列与枯草芽孢杆菌糖化α-淀粉酶的同源性为40%，与丙酮丁醇梭菌α-淀粉酶的同源性为27%。该酶作用于可溶性淀粉时，在pH 5.0至6.0时活性最佳。该酶在pH 5.5至8.5之间以及温度低于50℃时相对稳定。以可溶性马铃薯淀粉为底物时，该酶的Km为0.88 mg.ml-1，kcat为2,510 μmol还原糖.min-1.mg蛋白质-1。该酶既不具有支链淀粉酶活性也不具有葡聚糖酶活性，其作用于支链淀粉的活性是作用于直链淀粉活性的40%至70%。直链淀粉水解的主要终产物是麦芽糖、麦芽三糖和麦芽四糖。
