Suganuma T, Mizukami T, Moori K, Ohnishi M, Hiromi K
J Biochem. 1980 Jul;88(1):131-8.
An alpha-amylase [EC 3.2.1.1] from Streptomyces praecox was purified and its characteristic action, the conversion of maltotriose (G3) to maltose (G2) without appreciable formation of glucose (G1), was investigated. Isoelectric focusing or the glycogen adsorption procedure was employed after chromatography. Isoelectric focusing showed that the enzyme preparation after chromatographic separation comprises three isozymes. The preparation from the glycogen adsorption procedure showed the highest specific activity of any preparation of this enzyme ever obtained. Product analysis with uniformly labeled G3 revealed that at a high concentration (18 mM) of G3, much more G2 is produced than G1 (the product ratio G2/G1 is over 20), while at a lower concentration (10 microM) the reaction mixture was composed of nearly equimolar amounts of glucose and maltose. Based on the product analysis of reducing end-labeled G3 in addition to the above findings, the following conversion mechanism is proposed: Streptomyces alpha-amylase catalyzes transglycosylation to produce maltotetraose (G4) as a transient product which is immediately degraded into two molecules of G2 by a subsequent hydrolytic reaction, i.e., two molecules of G3 are converted into three molecules of maltose without appreciable formation of glucose.
对来自早生链霉菌的一种α-淀粉酶[EC 3.2.1.1]进行了纯化，并研究了其独特的作用，即麦芽三糖（G3）转化为麦芽糖（G2），而几乎不生成葡萄糖（G1）。色谱分离后采用等电聚焦或糖原吸附法。等电聚焦显示，色谱分离后的酶制剂包含三种同工酶。通过糖原吸附法制备的制剂显示出该酶所有制剂中最高的比活性。对均匀标记的G3进行产物分析表明，在高浓度（18 mM）的G3下，生成的G2比G1多得多（产物比率G2/G1超过20），而在较低浓度（10 microM）下，反应混合物由几乎等摩尔量的葡萄糖和麦芽糖组成。基于除上述发现之外对还原端标记的G3的产物分析，提出了以下转化机制：链霉菌α-淀粉酶催化转糖基化反应生成麦芽四糖（G4）作为瞬时产物，随后该瞬时产物通过水解反应立即降解为两分子G2，即两分子G3转化为三分子麦芽糖，几乎不生成葡萄糖。
