A method for quantifying radioactivity associated with protein in silver-stained polyacrylamide gels

A method is described in which individual proteins labeled with weak β-emitting radionuclides, separated by polyacrylamide gel electrophoresis, and stained with silver are released from the gel by the use of the periodate soluble cross-linking agent N,N′-dialyltartardiamide. The radioactivity can then be quantitated using liquid scintillation counting. The method is shown to be insensitive to reasonable variations in the intensity of staining as well as the gel volume over a practical range of gel slices. Recovery from the gel is extremely good with 93% of the counts associated with 14C-labeled proteins of known radioactive concentration being recovered. Analysis of a complex mixture of 3H-labeled proteins indicates resolution similar to that obtainable by autoradiography without the problems associated with quenching of autoradiographic signal by the staining procedure. The method is used to determine the amount of fucose and mannose incorporated into a putative cell adhesion protein during development of the cellular slime mold Dictyostelium purpureum.