A platelet function inhibitor purified from Vipera russelli siamensis (Smith) snake venom

By means of CM-Sephadex C-50 column chromatography and gel filtration on Sephadex G-75, a potent platelet function inhibitor was purified from Vipera russelli siamensis venom. It appeared as a single protein band on polyacrylamide gel electrophoresis in the presence or absence of SDS, and consists of 123 amino acid residues. Its NH2-terminal residue is serine. It showed the following characteristics: molecular weight, 13,800; isoelectric point, 10.4; LD50, 0.5 +/- 0.12 mg/kg (i.v.). The platelet inhibitor exhibited phospholipase A2 activity with a specific activity of 35 mumoles/min/mg. From 2 g of the venom, 70 mg of the purified inhibitor was obtained. Inhibition of human platelet aggregation induced by ADP or adrenaline was dose-dependent, with ID50 of 1.14 micrograms/ml or 0.37 microgram/ml, respectively. The platelet aggregation induced by thrombin or collagen was also inhibited and the inhibitory activity on platelet aggregation was heat stable (at 100 degrees C, 20 min) in an acidic medium (pH 5.8), while its phospholipase A2 activity was relatively heat labile under the same condition. The release of 3H-serotonin in platelets stimulated by ADP was also inhibited and this was positively correlated with inhibition of platelet aggregation induced by ADP (r = 0.998, P less than 0.002).