Oxygen dependent microbial killing is caused by Reactive oxygen species (ROS)
Reactive Oxygen Species. ROS are produced by the rapid assembly and activation of a multicomponent enzyme, phagocyte oxidase which oxidizes NADPH and, in the process, reduces oxygen to the superoxide anion. In neutrophils, this oxidative reaction is tightly linked to phagocytosis,
and is called the respiratory burst. Phagocyte oxidase is an enzyme complex consisting of at least seven proteins. In resting neutrophils, different components of the enzyme are located in the plasma membrane and the cytoplasm. In response to activating stimuli, the cytosolic protein components
translocate to the phagosomal membrane, where they assemble and form the functional enzyme complex. Thus, the ROS are produced within the phagolysosome, where they can act on ingested particles without damaging the host cell.
The azurophilic granules of neutrophils contain the enzyme myeloperoxidase (MPO), which, in the presence of a halide such as Cl−, converts H2O2 to hypochlorite, the active ingredient in household bleach. The latter is a potent anti-microbial agent that destroys microbes by halogenation or by oxidation of proteins and lipids.
The H2O2-MPO-halide system is the most efficient bactericidal system of neutrophils. Nevertheless, inherited deficiency of MPO only causes a modest increase in susceptibility to infection, emphasizing the redundancy of microbicidal mechanisms in leukocytes. H2O2 also is converted to hydroxyl radical (OH•), another powerful destructive agent
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