Myeloperoxidase of Human Neutrophilic Granulocytes as Chlorinating Enzyme

Abstract

Two p H ‐dependent spectral forms of myeloperoxidase have been described. Their absorption maxima in the Soret region were at 432 nm and 426 nm for acid and neutral pH, respectively. Chloride exerts an influence on the spectrum of peroxidase, mainly in acidic medium. Dissociation constants for the myeloperoxidase chloride complex and K m values for chloride in the chlorination reaction catalyzed by myeloperoxidase were determined. It was found that the affinity of chloride ions to the enzyme decreases with an increase of pH. Catalytic activity of myeloperoxidase in the reaction of incorporation of 36 Cl into aliphatic amino compounds such as taurine, β‐alanine, ethanolamine and diethanolamine was investigated. Primary amino groups were chlorinated to N ‐mono‐ or dichloramines, depending on the pH of the medium. The method of determination of 36 Cl‐labelled chlorocompounds in the presence of excess Na 36 Cl was described. The role of myeloperoxidase as chlorinating enzyme in the mechanism of the bactericidal effect on bacteria phagocytized by neutrophilic granulocytes is discussed.