The hydroxyl radical formation system in polymorphonuclear leukocytes.

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.