Organization and role of platelet membrane phospholipids as studied with phospholipases A2 from various venoms and phospholipases C from bacterial origin.
Phospholipases A2 from various snake or bee venoms and phospholipases C secreted as exotoxins by several bacteria have been used to study the transverse distribution of phospholipids in the platelet plasma membrane and their role in platelet activation. An asymmetric distribution was described for phospholipids, characterized by a preferential localization of sphingomyelin and phosphatidylcholine in plasma membrane outer leaflet, whereas the inner half contains almost all of the anionic procoagulant phosphatidylserine and phosphatidylinositol. Such a distribution might explain the latency of procoagulant activity in resting platelets and implies an intracellular localization of arachidonic acid, the precursor of prostaglandins and thromboxanes. The external arachidonic acid is involved in phospholipase A2-induced aggregation, whereas phospholipase C from Clostridium welchii stimulates platelets through a thromboxane-independent pathway. The latter one is directly linked to the formation of phosphatidic and lysophosphatidic acids, which are able to activate cells through calcium mobilization. So, phospholipase C represents an interesting tool for studying the biochemical processes accompanying stimulation, since it is shown that it mimics the effects of an intracellular phospholipase C, the role of which in platelet activation is discussed.
D000818:Animals; D001419:Bacteria / Q000201:enzymology; D001514:Bee Venoms; D001792:Blood Platelets / Q000648:ultrastructure*; D002462:Cell Membrane / Q000648:ultrastructure; D006801:Humans; D008563:Membrane Lipids / Q000097:blood*; D010740:Phospholipases; D010741:Phospholipases A; D054467:Phospholipases A2; D010743:Phospholipids / Q000097:blood*; D012910:Snake Venoms; D010738:Type C Phospholipases
D001514:Bee Venoms; D008563:Membrane Lipids; D010743:Phospholipids; D012910:Snake Venoms; D010740:Phospholipases; D010741:Phospholipases A; D054467:Phospholipases A2; D010738:Type C Phospholipases