Identification of ectoproteins of human platelets. Combination of radioactive labelling and two-dimensional electrophoresis

Two-dimensional gel electrophoresis combining isoelectric focussing of reduced or non-reduced proteins in the first dimension with electrophoresis in sodium dodecyl sulfate polyacrylamide gels in the second dimension enabled us to identify 25 ectoproteins in the non-reduced state and 32 in the reduced state. Gel electrophoresis in sodium dodecyl sulfate of non-reduced proteins in the first dimension followed by reduction and gel electrophoresis in sodium dodecyl sulfate in the second dimension was helpful in the identification of the major ectoproteins and indicated that at least seven additional components might be present in the region between 170 and 85 kdaltons. All major ectoproteins could readily be identified. Glycoprotein V showed only a small increase in apparent molecular weight on reduction. It was one of the most basic proteins with a PI value of 6.9. The majority of the ectoproteins were located at an isoelectric point of 5.7 with glycoproteins Ib, IIc, VI and VII as the most acidic components. A good agreement was observed between the three labelling techniques which indicates that almost all ectoproteins are glycoproteins containing sialic acid