HUMAN RECOMBINANT NONPANCREATIC SECRETED PLATELET PHOSPHOLIPASE-A2 HAS ANTICOAGULANT ACTIVITY INVITRO ON HUMAN PLASMA

Extracellular phospholipase A2 is secreted from the platelets upon activation by a stimulus such as thrombin (1,2). The secreted enzyme has been recently cloned and the recombinant protein produced (2). Snake venom PLA2 effect on platelet and coagulation has been extensively studied (for review see 3,4) and it has been proposed that the anticoagulant phospholipases may inhibit coagulation by competing with clotting proteins for the lipid surface (5). Structure function relationship for PLA2s with anticoagulant activity indicates that the activity is conferred by positively charged aminoacids between residues 54 and 77 (6). The corresponding segment of human recombinant secreted platelet PLA2 (r-hnps-PLA2) possesses five positively charged aminoacids in this region being at the identical positions to those of PLA2s with known anticoagulant activities (2). Here using human and rat plasma we have demonstrated for the first time that the recombinant human extracellular secreted platelet PLA2 increases activated partial thromboplastin time but not prothrombin time.