[Study on production of acrylamide by microbial method (II)--enzyme catalytic kinetics and de-active dynamics of nitrile hydratase].

The hydration reaction by microbial method is the crisis of the procedure of acrylamide production from acrylonitrile. This research studied the enzyme catalytic kinetics and de-active kinetics of nitrile hydratase in the type of free cell. Firstly, the effects of the concentration of cells, the temperature, pH value, the concentration of acrylonitrile and the concentration of acrylamide on the activity of nitrile hydratase was investigated. The result is that the temperature and the concentration of acrylamide are the most important among these factors. The activity of the nitrile hydratase was 5659 u/mL (broth) at 28 degrees C; the counterpart was only 663 u/mL (broth) at 5 degrees C. And the activity of NHase in solution of 45% acrylamide was just about half of that in solution of 5% acrylamide. After study on the relation of temperature and the reaction speed, It was found that the activation energy of the hydration of NHase was 65.57 kJ.mol-1. This paper studied the effects of concentration of cells, temperature, pH value, concentrations of acrylonitrile and acrylamide on the deactivation of Nhase, as well as the related enzyme de-active kinetics. The result also showed that the temperature and the concentration of acrylamide are the most important among these factors. In solution of 35% acrylamide, the residual activity was about 0% of the original value after 55 h; but in solution of 10% acrylamide, after the same period of time, the residual activity was 50% of the original one. It was also found that the concentration of acrylonitrile had little effect on the stability of NHase. The coefficient of deactivation at 28 degrees C was 21.77 times of the one at 5 degrees C. Correlating the temperature and the coefficient of deactivation, the activation energy of the de-active reaction was found to be 92.28 kJ.mol-1.