Structure and Properties of a Secretable Phospholipase A2 from Human Platelets
Phospholipases A2 (PLA2S) constitute a diverse family of enzymes that hydrolyze the sn-2 fatty acyl ester bond of phosphoglycerides liberating free fatty acids and lysophospholipids (Dennis, 1983). Mammalian extracellular PLA2S are abundant in pancreatic secretions, but are also present in plasma, lymph and pulmonary alveolar secretions (Vadas and Pruzanski, 1986). Intracellular PLA2s are found in all tissues and cells (van den Bosch, 1980), where they are located either in the cytosolic compartment associated with the plasma membrane or stored within organelles of the vacuolar system, such as secretory granules and lysosomes. The granule-associated PLA2s are designed to effectively degrade phospholipids upon exocytosis thereby serving either a digestive (Verheij et al., 1981) or an anti-microbial function (Elsbach, 1980). In contrast, the cytosolic PLA2s play a key role in the metabolism of cellular lipids, including the biosynthesis of specifically tailored phospholipids and the degradation of peroxidized phospholipids thus protecting membranes from oxidation damage (Waite, 1987). Furthermore, such PLA2s are involved in the generation of rate-limiting precursors for various types of lipid mediators (Irvine, 1982; Snyder, 1985) that transmit stimulatory signals to other cells or function as intracellular messengers (O’Flaherty, 1982; Larsen and Henson, 1983). This amplification mechanism is an integral part of the inflammatory response of tissues to injury that normally leads to removal of the inciting agent and repair of injured site.
KeywordsHuman Platelet Snake Venom PLA2 Activity Secretable Phospholipase Vacuolar System
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