Myeloperoxidase-hydrogen peroxide-chloride antimicrobial system: Effect of exogenous amines on antibacterial action against Escherichia coli

Abstract

Exogenous ammonium ions (NH4+) and amine compounds had a profound influence on the antibacterial activity of the myeloperoxidase-hydrogen peroxide-chloride system against E. coli. The rate of killing increased in the presence of NH4+ and certain guanidino compounds and decreased in the presence of α-amino acids, polylysine, taurine, or tris(hydroxymethyl)aminomethane. Myeloperoxidase catalyzed the oxidation of chloride to hypochlorous acid, which reacted either with bacterial amine or amide components or both or with the exogenous compounds to yield chloramine or chloramide derivatives or both. These nitrogen-chlorine derivatives could oxidize bacterial components. Killing was correlated with oxidation of bacterial components. The rate of oxidation of bacterial sulfhydryls increased in the presence of the compounds that increased the rate of killing and decreased in the presence of the other compounds. The reaction of HOCl with NH4+ yielded monochloramine (NH2Cl), which could be extracted into organic solvents. The N-Cl derivatives of bacterial components or polylysine, taurine, or tris(hydroxymethyl)aminomethane could not be extracted. The effect of NH4+ on killing is attributed to the ability of NH2Cl to penetrate the hydrophobic cell membrane and thus to oxidize intracellular components. Polylysine, taurine, and tris(hydroxymethyl)aminomethane formed high-molecular-weight, charged, or polar N-Cl derivatives that would be unable to penetrate the cell membrane. These results suggest an important role for leukocyte amine components in myeloperoxidase-catalyzed antimicrobial activity in vivo.