Myeloperoxidase inactivation in the course of catalysis of chlorination of taurine.

Abstract Myeloperoxidase (donor: hydrogen-peroxide oxidoreductase, EC 1.11.1.7) was isolated from leukocytes of patients with chronic granulocyte leukemia. In the presence of H 2 O 2 and Cl − at pH 4.0–6.6 the myeloperoxidase catalyses chlorination of taurine to monochloramine taurine and simultaneously undergoes inactivation. The myeloperoxidase inactivation rate depends on the concentration of H 2 O 2 and Cl − : both the initial rate of chlorination and myeloperoxidase inactivation rate increase with increasing concentration of H 2 O 2 . However, an increase in concentration of Cl − results in a decrease in enzyme inactivation. At a given H 2 O 2 concentration, myeloperoxidase inactivation is a first order reaction, which implied that the enzyme may react with a substrate a limited number of times.