The reaction of chloroperoxidase with chlorite and chlorine dioxide

Chloroperoxidase catalyzes the dismutation of chlorite-forming chloride, chlorine dioxide, chlorate, and oxygen as products. The yields of chlorine dioxide are variable because chloroperoxidase also catalyzes the decomposition of this compound and, in addition, moderate concentrations of chlorine dioxide inactivate the enzyme. Chloride, chlorate, and oxygen are the products of the decomposition of chlorine dioxide. The optimum pH for the enzymic of decomposition of both chlorite and chlorine dioxide is approximately pH 2.75. At this pH, 1 mole of chlorine dioxide is dismutated to 0.3 mole of chloride, 0.7 mol of chlorate, and 0.17 mole of oxygen. At the same pH, the complete decomposition of 1 mole of chlorite yields 0.4 mole of chloride, 0.6 mole of chlorate, and 0.13 mole of oxygen. During the inactivation of chloroperoxidase by chlorine dioxide, the Soret absorption band of the native enzyme is completely lost, and the enzyme becomes chlorinated. Kinetic parameters for the chlorite reaction have been determined. The Km value for chlorite obtained from various kinetic plots was about 10 mM. The catalytic rate constant for the formation of chlorine dioxide from chlorite was about 70,000 s-1.