Selenium toxicity: aminoacylation and Peptide bond formation with selenomethionine

Selenomethionine and methionine were compared as substrates for in vitro aminoacylation, ribosome binding, and peptide bond formation with preparations from wheat germ. Selenomethionine paralleled methionine in all steps of the translation process except peptide bond formation. Peptide bond formation with the initiating species of tRNA^Met demonstrated that selenomethionyl-tRNA^Met was less effective as a substrate than was methionyl-tRNA_f^Met. Participation of selenomethionine in the initiation process of translation could be expected to reduce the overall rate of protein synthesis and might aid in explaining selenium toxicity in selenium-sensitive plants.