The Hydroxyl Radical Formation System in Polymorphonuclear Leukocytes

Abstract

We studied the hydroxyl radical (OH·)-generating system in polymorphonuclear leukocytes (PMNs). When phenylalanine was incubated with the α, β and γ fractions prepared from pig polymorphonuclear leukocytes (PMNs) and hydrogen peroxide (H₂O₂), significant levels of formation of m- and o-tyrosine were observed in the α and β fractions, but not in the γ fraction. The amount of tyrosine formation per milligram of protein was greater with the β than with the α fraction. Further, when phenylalanine was incubated with α or β fractions with similar myeloperoxidase (MPO) activities in the presence of H₂O₂, tyrosine formation by the β fraction was also more effective. Using the β fraction in which the MPO activity was destroyed by heat treatment, no significant amount of tyrosine was formed. However, with the heat-treated β 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 β fraction. Tyrosine formation by the β 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.