Shen G J, Saha B C, Lee Y E, Bhatnagar L, Zeikus J G
Michigan Biotechnology Institute, Lansing 48910.
Biochem J. 1988 Sep 15;254(3):835-40. doi: 10.1042/bj2540835.
An extracellular beta-amylase from Clostridium thermosulphurogenes was purified 811-fold to homogeneity, and its general molecular, physico-chemical and catalytic properties were determined. The native enzyme was a tetramer of 210 kDa composed of a single type subunit; its 20 amino acid N-terminus displayed 45% homology with Bacillus polymyxa beta-amylase. The beta-amylase was enriched in both acidic and hydrophobic amino acids. The pure enzyme displayed an isoelectric point of 5.1 and a pH activity optimum of 5.5. The optimum temperature for beta-amylase activity was 75 degrees C, and enzyme thermostability at 80 degrees C was enhanced by substrate and Ca2+ addition. The beta-amylase hydrolysed amylose to maltose and amylopectin and glycogen to maltose and limit dextrins, and it was inhibited by alpha- and beta-cyclodextrins. The enzyme displayed kcat. and Km values for boiled soluble starch of 400,000 min-1 per mol and 1.68 mg/ml, respectively. The enzyme was antigenically distinct from plant beta-amylases.
对嗜热栖热硫化叶菌的一种胞外β-淀粉酶进行了纯化，纯化倍数达811倍，直至达到均一状态，并测定了其一般的分子、物理化学和催化特性。天然酶是一种由单一类型亚基组成的210 kDa四聚体；其20个氨基酸的N端与多粘芽孢杆菌β-淀粉酶有45%的同源性。该β-淀粉酶富含酸性和疏水氨基酸。纯酶的等电点为5.1，最适pH活性为5.5。β-淀粉酶活性的最适温度为75℃，通过添加底物和Ca2+可提高酶在80℃时的热稳定性。该β-淀粉酶将直链淀粉水解为麦芽糖，将支链淀粉和糖原水解为麦芽糖和极限糊精，并且它受到α-和β-环糊精的抑制。该酶对煮沸的可溶性淀粉的kcat.和Km值分别为每摩尔400,000 min-1和1.68 mg/ml。该酶在抗原性上与植物β-淀粉酶不同。
