Role of enzymatic activity in the antiplatelet effects of a phospholipase A2 from Ophiophagus hannah snake venom.
A phospholipase A2 (OHV A-PLA2) from the venom of Ophiophagus hannah (King cobra) is an acidic protein exhibiting antiplatelet activity. In in vitro tests, OHV APLA2 showed a marked inhibitory effect on platelet aggregation induced by ADP, collagen and arachidonic acid in both human whole blood and platelet-rich plasma in a dose-dependent manner. The antiplatelet effects of OHV A-PLA2 did not increase when preincubation times of platelets and OHV A-PLA2 were prolonged indicating phospholipid hydrolysis did not significantly contribute to the antiplatelet effects. Alkylation of active site His residue using p-bromophenacyl bromide resulted in the complete loss of enzymatic activity, but the modified enzyme retained more than 30% of its antiplatelet effects. These results indicate that the antiplatelet effects of OHV A-PLA2 appear to be independent of its enzymatic activity, and there are separate sites responsible for the catalytic and antiplatelet activities.
Huang
M Z
MZ
Department of Anatomy, National University of Singapore, Singapore.
Gopalakrishnakone
P
P
Kini
R M
RM
D000818:Animals; D004546:Elapid Venoms / Q000378:metabolism* / Q000494:pharmacology*; D006801:Humans; D010741:Phospholipases A / Q000378:metabolism* / Q000494:pharmacology*; D054467:Phospholipases A2; D010974:Platelet Aggregation / Q000187:drug effects; D010975:Platelet Aggregation Inhibitors / Q000378:metabolism* / Q000494:pharmacology*
D004546:Elapid Venoms; D010975:Platelet Aggregation Inhibitors; D010741:Phospholipases A; D054467:Phospholipases A2