A novel glucanotransferase, involved in the synthesis of a cyclomaltopentaose cyclized by an α-1,6-linkage [ICG5; cyclo-→6)-α-D-Glcp-(1→4)-α-D-Glcp-(1→4)-α-D-Glcp-(1→4)-α-D-Glcp-(1→4)-α-D-Glcp-(1→}], from starch, was purified to homogeneity from the culture supernatant of Bacillus circulans AM7. The pI was estimated to be 7.5. The molecular mass of the enzyme was estimated to be 184 kDa by gel filtration and 106 kDa by SDS–PAGE. These results suggest that the enzyme forms a dimer structure. It was most active at pH 4.5 to 8.0 at 50 °C, and stable from pH 4.5 to 9.0 at up to 35 °C. The addition of 1 mM Ca2+ enhanced the thermal stability of the enzyme up to 40 °C. It acted on maltooligosaccharides that have degrees of polymerization of 3 or more, amylose, and soluble starch, to produce ICG5 by an intramolecular α-1,6-glycosyl transfer reaction. It also catalyzed the transfer of part of a linear oligosaccharide to another oligosaccharide by an intermolecular α-1,4-glycosyl transfer reaction. Thus the ICG5-forming enzyme was found to be a novel glucanotransferase. We propose isocyclomaltooligosaccharide glucanotransferase (IGTase) as the trivial name of this enzyme.
一种新型
葡聚糖转移酶,参与合成由α-1,6-连接环化的环戊糖[ICG5;ICG5; cyclo-→6)-α-D-Glcp-(1→4)-α-D-Glcp-(1→4)-α-D-Glcp-(1→4)-α-D-Glcp-(1→4)-α-D-Glcp-(1→}]是从淀粉中分离纯化出来的。其 pI 值估计为 7.5。通过凝胶过滤估计该酶的分子量为 184 kDa,通过
SDS-PAGE 估计其分子量为 106 kDa。这些结果表明,该酶形成二聚体结构。该酶在 50 °C、pH 值为 4.5 至 8.0 的条件下活性最强,在 35 °C、pH 值为 4.5 至 9.0 的条件下稳定。添加 1 mM Ca2+ 可增强该酶的热稳定性,最高可达 40 °C。它作用于聚合度为 3 或以上的麦芽
寡糖、
直链淀粉和
可溶性淀粉,通过分子内 α-1,6-糖基转移反应生成 ICG5。它还能通过分子间α-1,4-糖基转移反应,催化部分线性
寡糖向另一种
寡糖的转移。因此,我们发现 ICG5 形成酶是一种新型的
葡聚糖转移酶。我们建议将异环麦芽
寡糖葡聚糖转移酶(IGTase)作为这种酶的简易名称。