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Wednesday, January 09, 2008

Phagocytosis - Respiratory burst involves the activation of Oxidase

032. During phagocytosis, the metabolic process called respiratory burst involves the activation of:

1. Oxidase

2. Hydrolase

3. Peroxidase

4. Dehydrogenase

Answer

1. Oxidase

Reference:

Chaterjee 6th Edition Page 18

Robbins 7th Edition Page 60

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Discussion

The pivotal role of the respiratory burst (which follows within seconds after phagocytes are activated) in the subsequent effective killing of catalase-positive microbes became evident from studies of patients with Chronic Granulomatous Disease.

Explanation

The NADPH oxidase that catalyzes the respiratory burst is found exclusively in phagocytes and remains dormant unless activated by a variety of particulate and soluble stimuli, such as opsonized microbes and chemotactic peptides.

Comments

These stimuli excite a transmembrane electron transport system in which NADPH on the cytoplasmic side of the membrane reduces oxygen through a series of reactions involving flavin adenine dinucleotide (FAD), several soluble cofactors, and membrane-associated cytochrome b. Oxygen is reduced through a univalent reduction to superoxide anion and is rapidly mutated to hydrogen perioxide and hydroxyl radicals.

Tips

The H2O2-MPO-Halide system is the most efficient bactericidal system in neutrophils

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