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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 polymorphonuclear leukocytes (PMNs) was found to be largely dependent on myeloperoxidase (MPO). Conversion was less than 10% of normal when MPO-deficient PMNs were employed; formation by normal PMNs 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 also 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 also 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 PMNs and by the MPO model system.
Insights
Myeloperoxidase (MPO) in white blood cells is key for ethylene production from thioethers. MPO-independent pathways also contribute, involving reactive oxygen species and singlet oxygen.
Area of Science:
- Biochemistry
- Cell Biology
- Immunology
Background:
- Phagocytic cells produce reactive oxygen species (ROS) during immune responses.
- Ethylene formation from thioethers is a marker of oxidative processes.
- Polymorphonuclear leukocytes (PMNs) are crucial immune cells involved in phagocytosis.
Purpose of the Study:
- To investigate the role of myeloperoxidase (MPO) in ethylene formation by phagocytosing PMNs.
- To identify MPO-independent mechanisms of ethylene production.
- To elucidate the reactive oxygen species involved in these processes.
Main Methods:
- Enzyme assays using MPO-deficient and normal PMNs.
- Inhibition studies with azide and cyanide.
- Analysis of ethylene formation in a cell-free MPO model system.
- Investigation of dye-sensitized photooxidation.
Main Results:
- Ethylene formation from methional and 2-keto-4-thiomethylbutyric acid by PMNs is largely MPO-dependent.
- MPO-deficient PMNs showed significantly reduced ethylene production (<10%).
- Azide and cyanide inhibited MPO-dependent ethylene formation.
- MPO-independent ethylene formation was observed in eosinophils and stimulated by azide in PMNs.
- Singlet oxygen involvement was suggested in dye-sensitized photooxidation.
Conclusions:
- MPO plays a major role in MPO-dependent ethylene formation by phagocytosing PMNs.
- MPO-independent pathways, potentially involving singlet oxygen, also contribute to ethylene production.
- Understanding these pathways provides insight into oxidative stress mechanisms in immune cells.