Role of catalytic function in the antiplatelet activity of phospholipase A2 cobra (Naja naja naja) venom.

Three acidic phospholipases A2 from Indian cobra (Naja naja naja) venom inhibited platelet aggregation in platelet rich plasma induced separately by ADP, collagen and epinephrine with different potencies. The order of inhibition was epinephrine > collagen > ADP. They did not inhibit platelet aggregation induced by arachidonic acid (10 microM). The inhibition was dependent on concentration of the protein and the time of incubation of the phospholipases A2 with platelet rich plasma. Parabromophenacyl bromide modified PLA2 enzymes lost their enzymatic activity as well as platelet aggregation inhibition activity suggesting the involvement of catalytic function in platelet aggregation inhibitory activity.