phospholipases

Enzymes that hydrolyze ester bonds in phospholipids. They comprise two types: aliphatic esterases (phospholipase A1, A2 and B) that release fatty acids, and phosphodiesterases (types C and D) that release diacyl glycerol or phosphatidic acid respectively. Type A2 is widely distributed in venoms and digestive secretions. Types A1, A2 and C (the latter specific for phosphatidyl inositol) are present in all mammalian tissues. Type C is also found as a highly toxic secretion product of pathogenic bacteria. Type B attacks monoacyl phospholipids and is poorly characterized. Type D is largely of plant origin. PLA2 Type II (a secreted enzyme, but not the same as the Type I digestive pancreatic enzyme) is probably very important in inflammation because its action can release arachidonic acid, the starting point for eicosanoid synthesis. Phosphatidylinositol bisphosphate-specific phospholipase C is important in generating diacylglycerol and inositol trisphosphate, both second messengers.