Preparative labeling of proteins with [ 35S]methionine

The most common technique for preparative labeling of proteins with radioisotopes for experimental purposes utilizes 125I. This isotope has certain limitations, including the emission of γ- and X-irradiation, the release of gaseous 125I 2 from solutions of Na 125I, and the potential for concentration of 125I in thyroid glands. We have discovered a means for labeling proteins rapidly and simply with [ 35S]methionine. The technique is applicable to a wide variety of proteins. Antibodies labeled by our technique remain functional.