Starved cultures of the soil amoeba suspended in phosphate-buffered saline exhibit stimulated O uptake in response to phagocytosis of either heat-killed yeast or latex beads. This phagocytosis-dependent (cyanide-insensitive) oxidative activity was observed when cells were isolated from either cyanide-stimulated or -inhibited cultures, and was therefore independent of the relative activities of the alternative mitochondrial oxidases known to exist in this organism. The extra O consumed during phagocytosis was stoichiometrically converted into O as detected by the rate of superoxide dismutase-inhibitable cytochrome reduction. Phagolysosomal membranes isolated after uptake of latex beads were enriched in a -type cytochrome which was spectrally similar to that present in immune phagocytes. Thus, the biochemical events during phagocytosis by either or immune phagocytes appear similar, suggesting that the ‘respiratory burst’ enzyme(s) responsible for O generation in these two cell types is structurally related.


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