Tanaka A, Karita S, Kosuge Y, Senoo K, Obata H, Kitamoto N
Faculty of Bioresources, Mie University, Japan.
Biosci Biotechnol Biochem. 1998 Nov;62(11):2127-32. doi: 10.1271/bbb.62.2127.
A fragment of the starch-binding domain (SBDF) of Aspergillus niger glucoamylase was prepared using recombinant DNA techniques, and its thermal unfolding was investigated by high-sensitivity differential scanning calorimetry (DSC). Thermal unfolding of SBDF was found to be reversible at pH 7 as expected from a DSC study of the whole enzyme molecule [Tanaka A. et al., J. Biochem., 117, 1024-1028 (1995)] but not reversible at acidic region. Numerical analysis of the DSC curves showed that the denaturation was two-state, and some of the SBDF molecules were oligomeric (average degree of oligomerization was 1.2) at pH 7. It was suggested that the denaturation temperature of SBDF was lower than that of the starch-binding domain in the whole enzyme molecule by about 4.5 degrees (decrease in the Gibbs energy change was 5.3 kJ mol-1) indicating a possibility that the starch-binding domain is stabilized by glycosylation of the domain itself, or by the highly glycosylated linker region.
利用重组DNA技术制备了黑曲霉葡萄糖淀粉酶淀粉结合结构域（SBDF）的一个片段，并通过高灵敏度差示扫描量热法（DSC）研究了其热变性。正如对整个酶分子进行DSC研究所预期的那样，发现SBDF在pH 7时的热变性是可逆的[田中A.等人，《生物化学杂志》，117，1024 - 1028（1995）]，但在酸性区域是不可逆的。DSC曲线的数值分析表明，变性是两态的，并且在pH 7时一些SBDF分子是寡聚体（平均寡聚化程度为1.2）。有人提出，SBDF的变性温度比整个酶分子中淀粉结合结构域的变性温度低约4.5摄氏度（吉布斯自由能变化减少5.3 kJ mol-1），这表明淀粉结合结构域可能通过其自身的糖基化或高度糖基化的连接区域而得到稳定。
