Ethylene formation by polymorphonuclear leukocytes. Role of myeloperoxidase.

Abstract

Ethylene formation from the thioethers, .beta.-methylthiopropionaldehyde (methional) and 2-keto-4-thiomethylbutyric acid by phagocytosing [human] polymorphonuclear leukocytes (PMN) was largely dependent on myeloperoxidase (MPO). Conversion was less than 10% of normal when MPO-deficient PMN [from 2 siblings with hereditary MPO deficiency] were employed. Formation by normal PMN was inhibited by the peroxidase inhibitors, azide and cyanide, and a model system consisting of MPO, H2O2, chloride (or bromide) and EDTA was found which shared many of the properties of the predominant PMN system. MPO-independent mechanisms of ethylene formation were identified. Ethylene formation from methional by phagocytosing eosinophils and by H2O2 in the presence or absence of catalase was stimulated by azide. The presence of MPO-independent, azide-stimulable systems in the PMN preparations was suggested by the azide stimulation of ethylene formation from methional when MPO-deficient leukocytes were employed. Ethylene formation by dye-sensitized photooxidation was demonstrated and evidence obtained for the involvement of singlet oxygen (1O2). These findings are discussed in relation to the participation of H2O2, hydroxyl radicals, the superoxide anion and 1O2 in the formation of ethylene by PMN and by the MPO model system.