The determination of similarities in amino acid composition among proteins separated by two-dimensional gel electrophoresis

A simple and rapid procedure has been developed to determine similarities in amino acid composition among cellular proteins separated by two-dimensional gel electrophoresis. Cells in tissue culture are simultaneously labeled with two different amino acids each tagged with a different radioisotope. The proteins are then separated on two-dimensional gels and their location on the gels determined by Coomassie-blue staining or autoradiography. Elution of the protein from the appropriate region of the gel followed by liquid scintillation counting yields an isotope ratio which reflects the ratio of the two amino acids in the protein. Examples of the use of this technique in analyzing mutant proteins, proteins altered by carbamylation, and cell proteins with similar amino acid composition (e.g., actin and tubulin) are given.