Tryptic Peptide Maps Of The Major Human Blood Platelet Membrane Glycoproteins, Ia, IIa, IIb, IIIa, IIIb and IIIc
Some major platelet membrane glycoproteins separated by 2-dimensional polyacrylamide gel electrophoresis (isoelectric focusing, discontinuous SDS-gel electrophoresis) have been characterized by 2-dimensional tryptic peptide mapping. Human platelets were isolated, washed and surface-labelled by lactoperoxidase-catalyzed iodination. Labelled platelets were solubilized in SDS and separated by 2-dimensional gel electrophoresis under non-reducing conditions in the 1st dimension and either reducing or non-reducing conditions in the 2nd dimension. Alternatively, labelled platelets were solubilized in sodium deoxy- cholate (1 %) and the glycosylated components were isolated by lectin affinity-chromatography on Lens culinaris lectin or concanavalin A lectin and separated by 2-dimensional gel electrophoresis. The glycoproteins were cut out from 6 % polyacrylamide gels, after being identified with Coomassie blue staining and indirect autoradiography by their pI and molecular weight. Tryptic maps were prepared according to the method of Elder et al. The tryptic maps of GPIa, IIa, IIb, IIIa, IIIb and IIIc are different, with each showing a characteristic pattern with the possible exception of Ia and IIb which showed certain similarities in both the reduced and non-reduced states. GPIIa which is clearly separated under non-reducing conditions, appears from its tryptic map to be present in the Ib region when reduced. Thus this technique clearly identifies each GP by a parameter in addition to pI and molecular weight.