EFFECT ON HUMAN PLATELET-AGGREGATION OF PHOSPHOLIPASE A(2) PURIFIED FROM HELODERMA-HORRIDUM (BEADED LIZARD) VENOM

By means of gel filtration, ionic exchange chromatography and DEAE-col umn HPLC, an acidic phospholipase A(2) (PLA(2)) was purified from bead ed lizard (Heloderma horridum) venom. The purified PLA is a single-cha in polypeptide, consisting of about 163 amino acid residues with a mol ecular mass of 19 000 Da as calculated by sodium dodecyl sulfate-polya crylamide gel electrophoresis and amino acid analysis. HHV-PLA showed a rather specific inhibitory effect on platelet aggregation induced by U46619 and epinephrine in human platelet-rich plasma in a dose- and t ime-dependent manner, whereas it had little effect on collagen- and AD P-induced aggregation. ATP-reIease reaction induced by various agonist s were dose- and time-dependently inhibited by HHV-PLA, even though pl atelet aggregation was apparently not affected in human washed platele ts. When HHV-PLA was chemically modified with p-bromophenacyl bromide, both of its enzymatic acitvity and antiplatelet activity were lost. F urthermore, exogenous lysophosphatidylcholine and HHV-PLA treated phos phatidylcholine inhibited platelet aggregation induced by U46619 in hu man washed platelets. In conclusion, PLA enzyme from H. horridum venom inhibits exclusively U46619- or thromboxane-induced platelet aggregat ion of human platelet-rich plasma probably by virtue of their PLA enzy matic acitvity on plasma phospholipids, converting phospholipids (e.g. , phosphatidylcholine) into lysophospholipids, which in turn interfere with the coupling of TXA(2) receptor and its signalling transduction system.