Convulxin(Cx), a high molecular weight glycoprotein which was purified by Sephadex G75 and Sepharose 4B chromatography, aggregates platelets of guinea-pigs, rabbits and humans (thresholds of 20-100 pico M for 400,000 platelets/μl). Aggregation and release reaction are plasma-independent, and do not require DFP-fibrinogen (DFP-fib), which increases the platelet response. Cx is not lytic for platelets. Neither ADP scavengers nor aspirin inhibit 2-4 suprathreshold concentrations of Cx. Bivalent metal chelation and PGI2 antagonize Cx. “Thrombinized” platelets lose granular ADP, and still respond to Cx in absence of DFP- fib. Cx-treated platelets are aggregated by ADP, thrombin (T) and arachidonic acid (AA), but are refactory to Cx and to collagen. Cx triggers release of 14C-AA metabolites from rabbit and human platelets, which was inhibited by phospholipase A2 inhibitors. “T-ized” platelets took 14C-AA and failed to release it if stimulated with T, but did so with Cx. Cxi.v.induces thrombocytopenia in rabbits and guinea-pigs, and bronchoconstriction in the latter, which is not blocked by aspirin. Cx is a very effective platelet-stimulating agent, free from proteolytic, amidolytic, esterasic, phospholipase and clotting activities. It probably interacts with T, ADP and thromboxane-independent receptors, and may share a component or a route with the mechanism triggered by collagen.
