Binding of acid mucopolysaccharides of Stichopus japanicus to washed human platelets

The binding of acid mucopolysaccharides of Stichopus japonicus Selenka (Sjamp) to washed human platelets was studied using [3H]Sjamp. The binding was rapid, reversible and with a saturable tendency. The binding reached to equilibrium at about 10 min, and 50% of [3H]Sjamp bound to the platelets at equilibrium within the first minute. When excess unlabeled Sjamp was added to the [3H]Sjamp binding suspension, [3H]Sjamp dissociated from the platelets rapidly and rather completely. Scatchard analysis revealed a class of binding sites with Kd = 2.3 +/- 0.7 micrograms/ml and Bmax = 4.5 +/- 1.2 micrograms/10(9) platelets. Separate experiments showed that the monoclonal antibody (McAb) SZ-21, a McAb to platelet membrane glycoprotein (GP) IIIa, weakened the binding, while McAb SZ-2 and SZ-22 (to GP Ib and GP IIb respectively) were ineffective. We also observed that heparin inhibited [3H]Sjamp binding to the platelets. These results indicated that the binding sites on platelets might be the Sjamp receptors. We conclude that receptor-Sjamp binding is an important process in platelet aggregation induced by Sjamp.