| Abstract: | The effect of temperature and pH on kinetic behavior of α-galactosidase of Mortierella vinacea was investigated on the hydrolysis of p-nitrophenyl-α-D -galactopyranoside (PNPG). A very unusual kinetic behavior was observed for the soluble α-galactosidase i.e., substrate inhibition diminished gradually with increasing temperature or near the neutral pH range, and the kinetics approached the ordinary Michaelis-Menten (MM) type. On the other hand, with decreasing temperature or in acidic pH range, substrate inhibition was accelerated. Therefore, Arrhenius plots based on the initial reaction rate did not give straight lines. Furthermore, the slope in the Arrhenius plot changed with substrate concentration, which would make the determination of a characteristic value using conventional methods meaningless. However, the Arrhenius plots of individual kinetic parameters in the rate equation resulted in straight lines in the temperature range 15 to 50°C. From this, the drastic change in kinetic behavior could be explained in connection with the temperature and pH dependence of kinetic parameters in the model. For mold pellets (whole-cell enzyme), however, the influence of temperature and pH was less apparent than that of soluble enzyme because of the limitation in intraparticle diffusion. By using the rate equation that was determined for soluble enzyme and the theoretically derived effectiveness factor, the overall reaction rate for mold pellets at various temperature and pH could be predicted to some extent. |
