Respiratory burst oxidase

Superoxide is formed (reaction 1) in the red blood cell by the auto-oxidation of hemoglobin to methemo-globin (approximately 3% of hemoglobin in human red blood cells has been calculated to auto-oxidize per day) in other tissues, it is formed by the action of enzymes such as cytochrome P450 reductase and xanthine oxidase. When stimulated by contact with bacteria, neutrophils exhibit a respiratory burst (see below) and produce superoxide in a reaction catalyzed by NADPH oxidase (reaction 2). Superoxide spontaneously dismu-tates to form H2O2 and O2 however, the rate of this same reaction is speeded up tremendously by the action of the enzyme superoxide dismutase (reaction 3). Hydrogen peroxide is subject to a number of fates. The enzyme catalase, present in many types of cells, converts... 

NADPH-oxidase j 2O2 + NADPH 20p + NADP -F H+ Key component of the respiratory burst Deficient in chronic granulomatous disease... 

The Respiratory Burst of Phagocytic Cells Involves NADPH Oxidase Helps Kill Bacteria... 

The electron transport chain system responsible for the respiratory burst (named NADPH oxidase) is composed of several components. One is cytochrome 6558, located in the plasma membrane it is a heterodimer, containing two polypeptides of 91 kDa and... 

Leukocytes are activated on exposure to bacteria and other stimuh NADPH oxidase plays a key role in the process of activation (the respiratory burst). Mutations in this enzyme and associated proteins cause chronic granulomatous disease. 

Inflammatory cell phenomenon are also contributors to lipid peroxidation. Activated neutrophils may adhere to damaged endothelium and amplify traumatic, ischaemic or ischaemia-reperfiision injury. Many cyclooxygenase products of the metabolism of atachidonic acid modulate the inflammatory responses of cells. Macrophages, neutrophils and microglia are important sources of reactive oxygen at the injury site. When activated, they produce a respiratory burst that is traced to activated nicotinamide adenine dinucleotide (NADPH/NADH) oxidase. 

Torres MA, Dangl JL (2005) Functions of the respiratory burst oxidase in biotic interactions, abiotic stress and development. Curr Opin Plant Biol 8 397 403 Torres MA, Jones JD, Dangl JL (2006) Reactive oxygen species signaling in response to pathogens. Plant Physiol 141 373-378... 

The respiratory burst of phagocytes is catalysed by a membrane-bound NADPH oxidase that is responsible for the reaction ... 

In the early 1960s in Japan, a b-type cytochrome was found in horse neutrophils and, because it bound CO, it was proposed to be functional during the respiratory burst. This work went largely unnoticed, but in 1978 Segal and Jones in the United Kingdom discovered that a b-type cytochrome became incorporated into phagolysosomes furthermore, this cytochrome was absent in some patients with CGD. These workers correctly proposed that it was a key component of the NADPH oxidase. This cytochrome was a landmark discovery in phagocyte research for a number of reasons ... 

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. 

Because electrode measurements of O2 uptake can detect intra- and extracellular oxidase activity, this assay can be used to measure the respiratory burst elicited by soluble and particulate stimuli. What is somewhat surprising is that, during stimulation of neutrophils with agonists such as fMet-Leu-Phe, the activated O2 uptake profile is biphasic (Fig. 5.11c). A rapid burst of O2 uptake (which coincides with measurements of cytochrome c reduction) is followed by a more sustained activity of lower magnitude. 

Akard, L. P., English, D., Gabig, T. G. (1988). Rapid deactivation of NADPH oxidase in neutrophils continuous replacement by newly activated enzyme sustains the respiratory burst. Blood 72, 322-7. 

Heyworth, P. G., Segal, A. W. (1986). Further evidence for the involvement of a phos-phoprotein in the respiratory burst oxidase of human neutrophils. Biochem. J. 239, 723-31. 

Okamura, N., Babior, B. M., Mayo, L. A., Peveri, P., Smith, R. M., Cumutte, J. T. (1990). The p61-phox cytosolic peptide of the respiratory burst oxidase from human neutrophils. J. Clin. Invest. 85, 1583-7. 

Volpp, B. D., Nauseef, W. M Donelson, J. E Moser, D. R Clark, R. A. (1989). Cloning of the cDNA and functional expression of the 47-kilodalton cytosolic component of human respiratory burst oxidase. Proc. Natl. Acad. Sci. USA 86, 7195-9. Watson, F., Robinson, J. J., Edwards, S. W. (1991). Protein kinase C dependent and independent activation of the NADPH oxidase of human neutrophils. J. Biol. Chem. 266, 7432-9. 

However, intracellular Ca2+ increases in themselves are insufficient to activate the oxidase because levels of this cation can be artificially increased in the absence of oxidase activity (e.g. by the addition of Ca2+ iono-phores such as ionomycin). Furthermore, activation of the oxidase by agonists such as PMA occurs in the absence of intracellular Ca2+ increases. Thus, if DAG is generated at sufficiently high concentrations to activate protein kinase C, then increases in intracellular Ca2+ are not required for oxidase activation. Furthermore, some agonists (e.g. LTB4 and PAF) generate substantial increases in intracellular Ca2+ but are poor activators of the respiratory burst. Also, there is a marked discrepancy between the concentrations of some agonists (e.g. fMet-Leu-Phe) required to activate either Ca2+ increases or oxidase activity. For example, maximal elevations in Ca2+ can occur at concentrations of fMet-Leu-Phe that are too low to activate the respiratory burst. It therefore appears that intracellular Ca2+ increases are not required to activate the respiratory burst per se, but are involved in the... 

It is known that protein kinase C can phosphorylate a number of key oxidase components, such as the two cytochrome b subunits and the 47-kDa cytoplasmic factor. This process is prevented by protein kinase C inhibitors such as staurosporine (although it is now recognised that this inhibitor is not specific for protein kinase C), which also inhibits the respiratory burst activated by agonists such as PMA. However, when cells are stimulated by fMet-Leu-Phe, translocation of pAl-phox to the plasma membrane can occur even if protein kinase C activity is blocked - that is, phosphorylation is not essential for the translocation of this component in response to stimulation by this agonist. Similarly, the kinetics of phosphorylation of the cytochrome subunits do not follow the kinetics of oxidase activation, and protein kinase C inhibitors have no effect on oxidase activity elicited by some agonists -for example, on the initiation of the respiratory burst elicited by agonists such as fMet-Leu-Phe (Fig. 6.14). Furthermore, the kinetics of DAG accumulation do not always follow those of oxidase activity. Hence, whilst protein kinase C is undoubtedly involved in oxidase activation by some agonists, oxidase function is not totally dependent upon the activity of this kinase. 

DEWAR STRUCTURES KEKULE STRUCTURES RESONANCE STABILIZATION ENERGY RESPIRATORY BURST OXIDASE NADPH OXIDASE RESPIRATORY EXCHANGE RATIO Restricted rotation,... 

Formation of the hydroxyl radical. Because the killing of certain microbes was dependent on the ability of PMNs to undergo the respiratory burst, the actual microbicidal species was sought. It had been shown that a potent oxidant was formed during the catalytic action of xanthine oxidase on xanthine an enzymic reaction which, like the PMN, produces both 07 and H2O2. This potent oxidant was proposed to be the hydroxyl radical formed by the reaction between O7 and H2O2 (reaction 4). Because such an oxidant seemed a likely candidate to mediate the microbicidal activity of PMNs, the formation of OH was assessed in PMNs. 

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