Saito K, Kondo K, Kojima I, Yokota A, Tomita F
Laboratory of Applied Microbiology, Research Group of Molecular Bioscience, Division of Applied Bioscience, Graduate School of Agriculture, Hokkaido University, Sapporo 060-8589, Japan.
Appl Environ Microbiol. 2000 Jan;66(1):252-6. doi: 10.1128/AEM.66.1.252-256.2000.
Streptomyces exfoliatus F3-2 produced an extracellular enzyme that converted levan, a beta-2,6-linked fructan, into levanbiose. The enzyme was purified 50-fold from culture supernatant to give a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The molecular weights of this enzyme were 54,000 by SDS-PAGE and 60,000 by gel filtration, suggesting the monomeric structure of the enzyme. The isoelectric point of the enzyme was determined to be 4.7. The optimal pH and temperature of the enzyme for levan degradation were pH 5.5 and 60 degrees C, respectively. The enzyme was stable in the pH range 3.5 to 8.0 and also up to 50 degrees C. The enzyme gave levanbiose as a major degradation product from levan in an exo-acting manner. It was also found that this enzyme catalyzed hydrolysis of such fructooligosaccharides as 1-kestose, nystose, and 1-fructosylnystose by liberating fructose. Thus, this enzyme appeared to hydrolyze not only beta-2,6-linkage of levan, but also beta-2,1-linkage of fructooligosaccharides. From these data, the enzyme from S. exfoliatus F3-2 was identified as a novel 2,6-beta-D-fructan 6-levanbiohydrolase (EC 3.2.1.64).
脱落链霉菌F3-2产生一种胞外酶，该酶可将β-2,6-连接的果聚糖左聚糖转化为蔗果四糖。该酶从培养上清液中纯化了50倍，在十二烷基硫酸钠-聚丙烯酰胺凝胶电泳（SDS-PAGE）上呈现单一条带。通过SDS-PAGE测得该酶的分子量为54,000，通过凝胶过滤测得为60,000，表明该酶具有单体结构。该酶的等电点测定为4.7。该酶降解左聚糖的最适pH和温度分别为pH 5.5和60℃。该酶在pH 3.5至8.0的范围内以及高达50℃时都很稳定。该酶以外切作用方式将左聚糖降解为主要产物蔗果四糖。还发现该酶通过释放果糖催化水解诸如1-蔗果三糖、黑曲霉糖和1-果糖基黑曲霉糖等低聚果糖。因此，该酶似乎不仅水解左聚糖的β-2,6-连接，还水解低聚果糖的β-2,1-连接。根据这些数据，脱落链霉菌F3-2的酶被鉴定为一种新型的2,6-β-D-果聚糖6-蔗果四糖水解酶（EC 3.2.1.64）。
