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The respiratory burst in a phagocyte is triggered when a bacterium is phagocytosed. During the phagocytosis of bacteria by macrophages and neutrophils,
the phagosome membrane pinches off and the microbe is endocytosed along with a small volume of extracellular fluid. The mechanisms discussed here
are based on studies in neutrophils and are still controversial.112 Electrons are removed from nicotinamide adenine dinucleotide phosphate (NADPH) in the
cytoplasm and transferred through the gp91phox component (which includes flavin adenine dinucleotide and two hemes) across the membrane, where they
reduce extracellular (or intraphagosomal) O2 to O2–. Protons left behind in the cell are extruded through voltage-gated proton channels (red). Some of the
reactive oxygen species (ROS) derived from O2– are indicated. Spontaneous or superoxide dismutase–catalyzed disproportionation of O2– produces
Source: Structure, Receptors, and Functions of Monocytes and Macrophages, Williams Hematology, 9e
hydrogen peroxide (H2O2), which may be converted to HOCl (hypochlorous acid, or household bleach) by myeloperoxidase (MPO). A. Traditional view of
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potential, intracellular pH (pHi), or external pH (pHo) and little change in ionic strength. Because proton channels are separate molecules and for the most
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reservedis not obligatory. The large depolarization that occurs during the respiratory burst
part operate Copyright
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in intact neutrophils and eosinophils is likely the most important factor that causes proton channels to open, although both pHi and pHo tend to change in a