title: Calcium regulation of phospholipase A2 is independent of calmodulin.
abstract: There are conflicting data in the literature as to whether or not the Ca2+ activation of phospholipase A2 is mediated by the calcium binding protein calmodulin. In the present study the membrane-bound phospholipase A2 enzymes in rat and human platelets were shown to be absolutely Ca2+ dependent but were not stimulated by the addition of calmodulin. A partially purified phospholipase A2 from rat platelet membrane, which contained little endogenous calmodulin, also was not stimulated by calmodulin addition. Both isolated and membrane-bound phospholipase A2 were inhibited by the non-specific calmodulin antagonist trifluoperazine but the inhibition was not overcome by adding calmodulin. There was thus no evidence from these studies that phospholipase A2 is calmodulin regulated.
mesh_terms: D000818:Animals; D001792:Blood Platelets / Q000201:enzymology*; D002118:Calcium / Q000502:physiology*; D002147:Calmodulin / Q000502:physiology*; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D066298:In Vitro Techniques; D010740:Phospholipases / Q000097:blood*; D010741:Phospholipases A / Q000037:antagonists & inhibitors / Q000097:blood*; D054467:Phospholipases A2; D051381:Rats; D014268:Trifluoperazine / Q000494:pharmacology
chemical_list: D002147:Calmodulin; D014268:Trifluoperazine; D010740:Phospholipases; D010741:Phospholipases A; D054467:Phospholipases A2; D002118:Calcium