The respiratory burst of bovine neutrophilis

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Abstract
1. A new method of preparation of bovine polymorphonuclear leukocytes (PMN) is described. The subcellular distribution of cytochrome b in resting and activated bovine PMN was compared to that of the .**GRAPHIC**. oxidase (assessed as NADPH cytochrome c reductase inhibited by superoxide dismutase). In resting PMN and in PMN activated by phorbol myristate acetate (PMA), cytochrome b was located into two membrane fractions, one of which was enriched in plasma membrane and cosedimented with alkaline phosphatase, while the other consisted of a denser material cosedimenting with markers of the specific and azurophil granules, i.e., the vitamin-B12-binding protein and myeloperoxidase respectively. During activation of PMN by PMA, 15-20% cytochrome b migrated from dense granules to the plasma membrane. 2. The distribution of the .**GRAPHIC**. oxidase and cytochrome b in subcellular particles was studied during the course of phagocytosis of PMA-coated latex beads by bovine PMN. At the onset of the respiratory burst, the phagocytic vacuoles arising from internalization of the plasma membrane were enriched in oxidase and alkaline phosphatase, but their specific content of cytochrome b was limited; in contrast, cytochrome b was predominant in denser membrane fractions cosedimenting with myeloperoxidase and the vitamin-B12-binding protein. After a few minutes of phagocytosis, a fraction of light vacuoles, slightly denser than the phagocytic vacuoles, became enriched in .**GRAPHIC**. oxidase, cytochrome b, the vitamin-B12-binding protein and myeloperoxidase. These vacuoles probably arose from the fusion of the phagocytic vacuoles with dense granules. 3. In bovine PMN supplemented with glucose and maintained in anaerobiosis, activation by PMA induced slow reduction of cytochrome b (60-70% in 15 min at 37.degree. C). Similar results were obtained with cytoplasts after activation by PMA (30% reduction in 3 min at 37.degree. C). Cytochrome b in a particulate fraction obtained by centrifugation at 100,000 .times. g of an homogenate of PMA-activated PMN, was slowly reduced upon addition of NADPH under anaerobiosis (less 20% in 20 min at 37.degree. C). No reduction occurred in the 100,000 .times. g fraction prepared from non-activated PMN. The Soret band of cytochrome b reduced by dithionite was displaced by CO only by 1-2 nm. At subsaturating concentrations, CO had no effect on the rate of O2 uptake by activated bovine PMN. 4. The specificity for NADPH and NADH of the .**GRAPHIC**. oxidase was assayed in the 100,000 .times. g fraction obtained from PMA-activated bovine PMN and in the phagocytic vacuoles prepared after phagocytosis of PMA-coated latex beads. In both types of particles, the preferential substrate was NADPH. On the other hand, NADH was a better electron donor for a superoxide-dismutase insensitive cytochrome c reductase (diaphorase). Deoxycholate enhanced the NADPH-dependent .**GRAPHIC**. oxidase of the 100,000 .times. g fraction, but not that of the phagocytic vacuoles, indicating free access of NADPH to its binding site on the oxidase in the latter case, but not the former. Direct oxidation of NADPH, but not of NADH, by O2 through the .**GRAPHIC**. oxidase was demonstrated in situ in PMA-activated bovine PMN permeabilized by deoxycholate.