Adhesion of platelets to collagen. The nature of the binding site from competitive inhibition studies

Abstract Platelet adhesion to collagen has been studied at 4° using a model system of washed platelets suspended in Tyrode buffer and a glass surface to which soluble collagen has been adsorbed. Platelets could be shown to adhere to this surface, though in fewer numbers than to collagen fibers and without leading to aggregation. Adhesion of platelets to collagen is thus an independent event which does not necessarily produce aggregation. Preincubation of platelets with soluble collagen, denatured soluble collagen, pepsin- and periodate-treated soluble collagen and cyanogen bromide peptides all decreased the ability of platelets to bind to the soluble collagen coated surface. Similar effects arose, moreover, with the synthetic copolypeptides (Gly-Pro-Ala-Gly-Pro-Pro) n , (Gly-Pro-Pro) n and (Pro 2 -Gly) n . In fact the homopolymers polyproline and polyhydroxyproline (but not proline or hydroxyproline) as well gave effects similar to those of the collagen materials. The effect was rather specific since preincubation with plasma proteins and synthetic polypeptides based on other major amino acids present in collagen, viz. polyalanine, polyglutamic acid, polyaspartic acid, polyarginine and polylysine, did not inhibit the binding of platelets. It would therefore appear that proline and hydroxyproline are the important, if perhaps not the only, determinants involved in platelet recognition of collagen. The choice of the more stable model test system of soluble collagen coated surfaces at 4° could be justified since similar effects of the test materials could be demonstrated also at 30°.