Chlorination by the Myeloperoxidase-H2O2-CI-Antimicrobial System at Acid and Neutral pH

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Abstract
The oxidation of Cl- ion by H2O2 yielding Cl+ is catalyzed by myeloperoxidase (MPO) prepared from human PMN [polymorphonuclear leukocytes]. In this reaction H2O2 and Cl- serve as substrates. Affinity (apparent) studies between MPO and Cl- and MPO and H2O2 were done. Both (apparent) affinities vary according to pH. The higher the pH, the less the affinity for Cl-. The affintity between MPO and H2O2 increases with pH. The dissociation constant of the MPO-Cl- enzyme substrate complex is affected by the 2nd substrate, H2O2. The effect of H2O2 on the MPO-Cl- affinity is competitive. The MPO-H2O2 affinity is decreased with increasing Cl- concentration. This influence is also competitive. The optimal pH for chlorination is dependent on the [H2O2]/[Cl-] ratio. The relationship of pH, H2O2 and Cl- concentrations may be expressed by the following formula: pH = log [Cl-] .times. 560/[H2O2]. Using the formula, it can be shown that optimal chlorination may occur between pH 4.0 and 7.4.