Demerdash M, Attia R M
Agric. Res. Center, Microbiol. Res. Dept., Giza-Egypt.
Zentralbl Mikrobiol. 1992 Oct;147(7):477-82.
The kinetic of thermal deactivation of CMC-ase activity of A. niger, locally isolated, was studied. The enzyme was found to be more stable in temperatures below 40 degrees C. The rates of activity decay were significant at high temperatures and can be described as a first-order kinetic model. Deactivation rate constants (Kd) were determined at different temperatures (30, 40, 55 and 65 degrees C). Kd value for CMC-ase activity decay at 65 degrees C was 28 times higher than its value at 30 degrees C. An Arrhenius type temperature dependence of Kd was found, and the activation energy (Ea) of the thermal deactivation was calculated to be 8400 cal/mole. Thermodynamic quantities (delta H) and (delta S) for deactivation process were 7700 and 11.9 cal/mole, respectively. The change of two kinetic parameters, i.e. Vmax and Km under deactivation conditions, was discussed.
对本地分离的黑曲霉羧甲基纤维素酶（CMC-ase）活性的热失活动力学进行了研究。发现该酶在40摄氏度以下的温度中更稳定。在高温下活性衰减速率显著，且可用一级动力学模型描述。在不同温度（30、40、55和65摄氏度）下测定了失活速率常数（Kd）。65摄氏度时CMC-ase活性衰减的Kd值比30摄氏度时高28倍。发现Kd呈现阿累尼乌斯型温度依赖性，热失活的活化能（Ea）经计算为8400卡/摩尔。失活过程的热力学量（ΔH）和（ΔS）分别为7700和11.9卡/摩尔。讨论了失活条件下两个动力学参数即Vmax和Km的变化。
