Role of catalytic function in the antiplatelet activity of phospholipase A(2) cobra (Naja naja naja) venom

Three acidic phospholipases A(2) from Indian cobra (Naja naja naja) venom i nhibited platelet aggregation in platelet rich plasma induced separately by ADP, collagen and epinephrine with different potencies. The order of inhib ition was epinephrine > collagen > ADP. They did not inhibit platelet aggre gation induced by arachidonic acid (10 muM). The inhibition was dependent o n concentration of the protein and the time of incubation of the phospholip ases A(2) with platelet rich plasma. Parabromophenacyl bromide modified PLA (2) enzymes lost their enzymatic activity as well as platelet aggregation i nhibition activity suggesting the involvement of catalytic function in plat elet aggregation inhibitory activity.