A comparison of techniques used to study externally oriented proteins and glycoproteins of human blood platelets

Abstract

The surface of whole washed human platelets was labelled by a variety of methods specific for proteins or for carbohydrates. The labelled platelets were solubilized and analysed by electrophoresis by means of a Laemmli slab gel system. Galactose oxidase plus tritiated sodium borohydride weakly labelled five glycoprotein bands indicating that few free terminal galactose residues are present on platelet membrane glycoproteins. Pretreatment with neuraminidase before galactose oxidase and tritiated sodium borohydride greatly increased both labelling intensity and the number of bands labelled indicating that most of the glycoprotein chains terminate with sialic acid. After treatment, glycoprotein Ib moved to a slightly higher molecular weight. Labelling with periodate and tritiated borohydride gave intensely labelled glycoprotein bands which correlated well with those observed by PAS staining. Lactoperoxidase plus 125I labelled protein bands, which could be correlated with the bands labelled by the carbohydrate specific techniques. Simultaneous analysis of platelets from single donors labelled by a variety of techniques offers a reliable approach to the investigation of the structures of the platelet surface proteins and glycoproteins.