Surface Labeling of Human Platelets by Reductive Methylation

A simple, reproducible method for the specific labeling of the surface proteins of human platelets with tritium is described. The labeled platelets were analyzed by two-dimensional gel electrophoresis (isoelectric focusing/sodium dodecyl sulfate-polyacrylamide gel electrophoresis) followed by fluorography and the results compared with those obtained by conventional methods. Reductive methylation gave an intense labeling of membrane glycoproteins. There was no cross-linking of the labeled membrane proteins by formaldehyde nor could clear evidence be found that inner proteins were labeled by permeation of the reagents through the plasma membrane. As well as previously described platelet membrane glycoproteins, several others could be detected that were not invariable seen using labeling techniques.