In Vitro Incorporation of Selenomethionine into Protein by Vigna radiata Polysomes

Vigna radiata polysomes efficiently incorporated [(75)Se]selenomethionine, [(14)C]methionine, and [(14)C]leucine in vitro. The optimal conditions for translation were determined to be 4.8 millimolar Mg(2+), 182 millimolar K(+), and pH 7.4. The rates of incorporation of [(75)Se]selenomethionine and [(14)C]methionine were similar when measured separately, but [(75)Se]selenomethionine incorporation was 35% less than [(14)C]methionine incorporation when both amino acids were present in equal molar concentrations. Polyacrylamide gel electrophoresis of the hot trichloroacetic acid precipitable translation products demonstrated synthesis of high molecular weight labeled proteins in the presence of [(75)Se]selenomethionine or [(35)S]methionine. No major differences in molecular weights could be detected in the electrophoretic profiles. Utilization of selenomethionine during translation by Vigna radiata polysomes establishes a route for the assimilation of selenomethionine by plants susceptible to selenium toxicity.