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The hydroxyl radical formation system in polymorphonuclear leukocytes
N Kawakami1, T Hayakawa, S Shimohama
1Department of Environmental Biochemistry, Kyoto Pharmaceutical University, Japan.
Abstract:
We studied the hydroxyl radical (OH*)-generating system in polymorphonuclear leukocytes (PMNs). When phenylalanine was incubated with the alpha, beta and gamma fractions prepared from pig polymorphonuclear leukocytes (PMNs) and hydrogen peroxide (H2O2), significant levels of formation of m- and o-tyrosine were observed in the alpha and beta fractions, but not in the gamma fraction. The amount of tyrosine formation per milligram of protein was greater with the beta than with the alpha fraction. Further, when phenylalanine was incubated with alpha or beta fractions with similar myeloperoxidase (MPO) activities in the presence of H2O2, tyrosine formation by the beta fraction was also more effective. Using the beta fraction in which the MPO activity was destroyed by heat treatment, no significant amount of tyrosine was formed. However, with the heat-treated beta fraction and MPO preparations from human neutrophils in the presence of H2O2, the amount of tyrosine formation increased with the addition of increasing amounts of heat-treated beta fraction. Tyrosine formation by the beta fraction in the presence of H2O2 was significantly reduced by OH* scavengers. The above results suggest the existence of an OH*-generating system in which MPO and H2O2 participate in the granules of PMNs and, especially, in specific granules, there may exist some factors that cause more effective OH* generation.
Insights
Polymorphonuclear leukocytes (PMNs) generate hydroxyl radicals (OH*) via myeloperoxidase (MPO) and hydrogen peroxide (H2O2). Specific granule factors enhance this OH* generation, crucial for understanding immune responses.
Area of Science:
- Immunology
- Cellular Biology
- Biochemistry
Background:
- Polymorphonuclear leukocytes (PMNs) are key immune cells involved in host defense.
- Hydroxyl radical (OH*) generation is a critical component of the oxidative burst in PMNs.
- Understanding the specific mechanisms of OH* generation is vital for comprehending inflammatory processes.
Purpose of the Study:
- To investigate the hydroxyl radical (OH*)-generating system within polymorphonuclear leukocytes (PMNs).
- To identify factors within PMN granules that contribute to OH* production.
- To elucidate the roles of myeloperoxidase (MPO) and hydrogen peroxide (H2O2) in this system.
Main Methods:
- Incubation of phenylalanine with different PMN fractions (alpha, beta, gamma) and hydrogen peroxide (H2O2).
- Quantification of tyrosine formation as a marker for OH* generation.
- Heat inactivation of MPO activity and subsequent MPO addition experiments.
- Assessment of OH* scavenger effects on tyrosine formation.
Main Results:
- Significant m- and o-tyrosine formation observed with alpha and beta PMN fractions, indicating OH* generation.
- Beta fraction showed more effective tyrosine formation per milligram of protein compared to the alpha fraction.
- MPO activity was essential for OH* generation; heat inactivation abolished activity, while MPO addition restored it.
- OH* scavengers significantly reduced tyrosine formation, confirming OH* involvement.
- Specific granule factors appear to enhance OH* generation.
Conclusions:
- A hydroxyl radical (OH*)-generating system exists in PMNs, involving myeloperoxidase (MPO) and hydrogen peroxide (H2O2).
- This system is particularly active within PMN granules, especially specific granules.
- Factors within specific granules likely enhance the efficiency of OH* generation by PMNs.