Reactive oxidant production during the respiratory burst

Over the years, there have been numerous reports of oxidase preparations that contain polypeptide components, additional to those described above. As yet no molecular probes are available for these, and so their true association with the oxidase is unconfirmed. There are many reports in the literature describing the role of ubiquinone as an electron transfer component of the oxidase, but its involvement is controversial. Quinones (ubiquinone-10) have reportedly been detected in some neutrophil membrane preparations, but other reports have shown that neither plasma membranes, specific granules nor most oxidase preparations contain appreciable amounts of quinone, although some is found in either tertiary granules or mitochondria. Still other reports suggest that ubiquinone, flavoprotein and cytochrome b are present in active oxidase preparations. Thus, the role of ubiquinone and other quinones in oxidase activity is in doubt, but the available evidence weighs against their involvement. Indeed, the refinement of the cell-free activation system described above obviates the requirement for any other redox carriers for oxidase function. 

4 Reactive oxidant production during the respiratory burst 

The reaction of myeloperoxidase with H2O2 is complex and depends upon the concentration of H2O2 and the presence of other factor(s) within the microenvironment (Fig. 5.9). The Fe in native myeloperoxidase is in the Fe III (oxidised) state (MP03+, ferric myeloperoxidase), and this reacts with low (equimolar) concentrations of H2O2 to form compound 1, a short-lived inter- 

The transient production of compounds II and in has been reported during stimulation of neutrophils by fMet-Leu-Phe and PMA, respectively. Ferric myeloperoxidase and compound III show catalase activity, even in the presence of CP, when H2O2 concentrations are in excess of 200 pM. Thus, under these conditions, O2 formation will occur at the expense of HOCI forma- 

It has been reported that, depending upon the stimulus used, 40-70% of the O2 consumed during the respiratory burst appears in HOC1 via the reaction  

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Additionally, the myeloperoxidase system even regulates the duration of the respiratory burst because neutrophils from patients with myeloperoxidase deficiency (see 8.3) generate more reactive oxidants than control cells. Also, when myeloperoxidase is inhibited with a specific antibody or a specific inhibitor such as salicylhydroxamic acid, the duration of the respiratory burst, but not the maximal rate of oxidant production, is extended. This indicates that a product of the myeloperoxidase system inhibits the NADPH oxidase and so self-regulates reactive oxidant production during inflammation. 

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