Th-P15:24 Decrease in PH strongly enhances aggregation of sphingomyelinase-treated LDL particles and their binding to human aortic proteoglycans

Recently, J. R. Kanofsky et al. (1988, J. Biol. Chem.263, 9692–9696) reported that human eosinophils generated modest amounts of singlet oxygen. In the mechanism proposed, hypobromous acid (made from the peroxidase-catalyzed oxidation of bromide ion) reacted with hydrogen peroxide to form singlet oxygen. In contrast, human neutrophils, which generate both hypochlorous acid and hydrogen peroxide, do not make singlet oxygen. The failure of human neutrophils to generate singlet oxygen is due in part to the trapping of hypochlorous acid by endogenous amines. In this paper, I show that amino acids are much more effective traps for hypochlorous acid than for hypobromous acid. Glycine totally inhibits singlet oxygen generation from a model enzyme system composed of chloroperoxidase, hydrogen peroxide, and chloride ion, but causes only a 35% reduction in singlet oxygen generation from an analogous enzyme system containing bromide ion instead of chloride ion. The products of the reaction of hypobromous and glycine (presumably an equilibrium mixture of N-bromoglycine, N,N-dibromoglycine, and hypobromous acid) retain the ability to react with hydrogen peroxide to form singlet oxygen. In contrast, the products of the reaction of hypochlorous acid and glycine do not react with hydrogen peroxide to produce singlet oxygen. Similar results were obtained for l-alanine, l-arginine, l-asparagine, l-aspartic acid, l-cystine, l-glutamic acid, l-glutamine, l-histidine, l-lysine, l-phenylalanine, l-proline, l-serine, and l-tyrosine. Thus, bromine derivatives of amino acids may act as intermediates in the peroxidasecatalyzed generation of singlet oxygen.