Further Studies on the Glycoprotein Composition of Normal Human, Bernard-Soulier and Thrombasthenic Platelets

Abstract

The glycoprotein composition of normal human platelets has been more precisely defined using SDS-polyacrylamide gel electrophoresis and comparing SDS-phosphate, SDS-tris and SDS-trisglycine buffer systems. At least 10 glycoproteins may be identified including a previously unlocated high M. Wt. (in excess of 500,000 daltons) membrane glycoconjugate, glycocalicin and the intracellular thrombin sensitive protein. A much diminished staining for carbohydrate of membrane GP la and lb, and of glycocalicin, were the major characteristics observed for Bernard-Soulier (B-S) platelets which also gave a reduced agglutination with wheat germ lectin. These abnormalities were much greater than the changes observed using neuraminidase-treated control platelets. The B-S platelets aggregated rapidly in the presence of thrombin, an event difficult to reconcile with glycocalicin being the proposed receptor for thrombin on the platelet surface. Membrane GP lib and also GP Ilia (depending on the conditions of membrane solubilization and the subsequent SDS-polyacrylamide gel elctrophoresis) both appeared to be absent in thrombasthenic platelet membranes. These abnormalities were often accompanied by an increased staining for carbohydrate of the members of the GP I family. With both the control and the pathological platelets the rate of migration and the staining intensities of the glycoprotein bands depended on the gel buffer system and the presence or absence of reducing agent during the initial soubilization. The results have indicated structural relationships and possible interconvertions between individual GP bands. They have also more closely defined the glycoprotein abnormalities in B-S and thrombasthenic platelets.