Summary
Platelet membrane glycoproteins (GP) are involved in platelet adhesion and aggregation.
The glycoprotein IIb-IIIa complex (GP IIbIIIa) is a Ca2+-dependent heterodimer that binds fibrinogen and other adhesive proteins, thereby
mediating platelet aggregation and adhesion. We have purified two major glycoproteins
from pig platelets by Concanavalin A-Sepharose, Heparin-Sepharose and Sephacryl S-300
HR chromatography (Fitzgerald et al. Anal Biochem, 1985): i) the GP IIb-IIIa complex, GP IIb Mr = 140,000 and GP IIIa a single chain
of Mr = 95,000-100,000; and ii) a predominant glycoprotein of high molecular weight,
the propolypeptide of von Willebrand factor (Mr = 80,000-100,000). Western-blot analysis
of the purified GP IIb-IIIa showed that only certain monoclonal antibodies against
the human receptor specifically recognize the porcine complex. Differences between
the porcine and human GP IIb-IIIa glycoproteins could partially explain the decreased
inhibitory effects of GP IIb/IIIa-antagonists (against the human receptor) in porcine
platelets.