Abstract
Phagocytosis or the interaction of certain agents with membrane receptors results in greatly enhanced rates of leucocytes oxygen metabolism (respiratory burst) and production of active oxygens such as superoxide (O-2) which rapidly dismutes to yield hydrogen peroxide (H2O2) and hydroxyl radicals (OH⋅) . Active oxygens produced are used to generate powerful microbicidal agents such as hypochlorous acid (HOCl) . The respiratory burst results from the activation of an enzyme (NADPH oxidase), dormant in resting cells, which catalyzes the following reaction: NADPH+2O-2→2O-2+NADP++H+. The oxidase is considered to be an FAD-requiring enzyme. Cytochrome b558 which is found uniquely in phagocytes is also proposed to be an electron carrier. The mechanism by which the oxidase is activated on stimulation of the cells is not clearly understood. Many informations, however, have been gathered concerning the activation event. Calcium ion is essential for the activation and protein phosphorylation by protein kinase C which is activated by diacylglycerol, produced through phosphatidylinositol turnover, appears to be involved in the activation reaction. Cyclic AMP and the products of arachidonic acid cascade regulate the superoxide production.
