In Vitro Incorporation of Selenomethionine into Protein by Vigna radiata Polysomes

Vigna radiata polysomes efficiently incorporated ⁷⁵Se]selenomethionine, ¹⁴C]methionine, and ¹⁴C]leucine in vitro. The optimal conditions for translation were determined to be 4.8 millimolar Mg²⁺, 182 millimolar K⁺, and pH 7.4. The rates of incorporation of ⁷⁵Se]selenomethionine and ¹⁴C]methionine were similar when measured separately, but ⁷⁵Se]selenomethionine incorporation was 35% less than ¹⁴C]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 ⁷⁵Se]selenomethionine or ³⁵S]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.