Abdel-Naby M A
Department of Chemistry of Natural and Microbial Products, National Research Center, Dokki, Cairo, Egypt.
Microbiol Res. 1999 Sep;154(2):213-8. doi: 10.1016/S0944-5013(99)80017-2.
Cellobiase from Aspergillus niger was glycosylated by covalent coupling to cyanogen bromide activated dextran. The conjugated enzyme retained 62% of the original specific activity exhibited by the native cellobiase. The optimum pH as well as the pH stability of the conjugated form remain almost the same as for the native enzyme. Compared to the native enzyme, the conjugated form exhibited a higher optimal reaction temperature and energy of activation, a higher K(m) (Michaelis constant) and lower Vmax (maximal reaction rate), and improved thermal stability. The thermal deactivation of the native and conjugated cellobiase obeyed the first-order kinetics. The calculated half-life values of heat inactivation at 60, 70 and 80 degrees C was 10.7, 6.25, and 4.05 h, respectively, whereas at these temperatures the native enzyme was less stable (half-life of 3.5, 1.69, and 0.83 h, respectively). The deactivation rate constant at 80 degrees C for the conjugated cellobiase is about 7.9 x 10(-2) h-1, which is lower than that of the native enzyme (36.0 x 10(-2) h-1). The activation energy for denaturation of the native enzyme is about 10.58 kcal/mol, which is 7.25 kcal/mol lower than that of the conjugated enzyme. The effect of different surfactants and some metal ions on the activity of the conjugated cellobiase has been investigated.
黑曲霉纤维二糖酶通过与溴化氰活化的葡聚糖共价偶联进行糖基化。偶联后的酶保留了天然纤维二糖酶所表现出的原始比活性的62%。偶联形式的最佳pH值以及pH稳定性与天然酶几乎相同。与天然酶相比，偶联形式表现出更高的最佳反应温度和活化能、更高的K(m)（米氏常数）和更低的Vmax（最大反应速率），并具有更好的热稳定性。天然和偶联的纤维二糖酶的热失活遵循一级动力学。在60、70和80℃下计算出的热失活半衰期值分别为10.7、6.25和4.05小时，而在这些温度下天然酶的稳定性较差（半衰期分别为3.5、1.69和0.83小时）。偶联的纤维二糖酶在80℃下的失活速率常数约为7.9×10⁻² h⁻¹，低于天然酶（36.0×10⁻² h⁻¹）。天然酶变性的活化能约为10.58 kcal/mol，比偶联酶低7.25 kcal/mol。研究了不同表面活性剂和一些金属离子对偶联纤维二糖酶活性的影响。
