Ubiquinone content and respiratory burst activity of latex-filled phagolysosomes isolated from human neutrophils and evidence for the probable involvement of a third granule.

Human neutrophils prepared from fresh blood were activated with either latex o r latex plus phorbol myristate acetate. Phagolysosomes subsequently isolated by gradient centrifugation were enriched 6or 4-fold, respectively, in respiratory burst activity as measured by superoxide dismutase-sensitive NADPH-cytochrome c reductase activity. The phagolysosomes were also enriched about 4-fold in ubiquinone content. These enrichments were significantly greater than that of specific granules o r azurophilic granules (each 1-2fold) and, therefore, indicate that formation of respiratory burst activity in the phagolysosome probably involves a third, ubiquinone-rich granule. The results provide further evidence that ubiquinone is necessary for the respiratory burst in neutrophils. First, the above cell fractionation studies indicate that ubiquinone and reductase activity co-purify. Also, the isolated phagolysosomes exhibit hydroquinone oxidase activity. In addition, inhibitors of the reductase activity were used to probe the function of ubiquinone in neutrophils. Quercetin, a compound that affects ubiquinone-dependent reactions, was a strong inhibitor of the NADPH-cytochrome c reductase activity of phagolysosomes. Furthermore, oxygen metabolism in neutrophils and the alternative respiratory pathway of plants have notable characteristics in common. Both are insensitive to inhibition by cyanide and azide, and salicylhydroxamate, a known inhibitor of the alternative oxidase in plants, was found to inhibit oxygen metabolism in neutrophils.