Comparative reactivities of various biological compounds with myeloperoxidase-hydrogen peroxide-chloride, and similarity of the oxidant to hypochlorite.

The reactivities of myeloperoxidase-H2O2-Cl- and sodium hypochlorite with amino acids, uric acid, NADH, ascorbic acid, ADP, albumin, haemoglobin, alpha 1-antitrypsin and some hydroxyl radical scavengers have been compared. The ability of each compound to inhibit chlorination of monochlorodimedon by both oxidants was measured. Relative reaction rates varied over a range of 10(5), but the reactivities of the two oxidants with each compound were very similar, from which it is concluded that the reactions of hypochlorite accurately reflect those of the myeloperoxidase system. Thiol compounds (cysteine and GSH) and methionine were more than 100-times more reactive than other amino acids, which had comparable reactivity to NADH and uric acid. Benzoate, dimethylsulphoxide and formate were very much less reactive. The significance of these reactions of myeloperoxidase in microbial killing and inflammation is discussed.