Abstract
In order to clarify the mechanisms of selenocysteine incorporation into glutathione peroxidase, some evidence to show the in vitro conversion of phosphoseryl-tRNA to selenocysteyl-tRNA is reported. [ 3H]Phosphoseryl-tRNA was incubated in a reaction mixture composed of SeO 2, glutathione and NADPH in the presence of selenium-transferase partially purified. Analyses of amino acids on the product tRNA showed that a part (4%) of [ 3H]phosphoseryl-tRNA was changed to [ 3H]selenocysteyl-tRNA. The conversion from seryl-tRNA su or major seryl-tRNA IGA was not found. Selenium-transferase was essential for the conversion. [ 3H]Selenocysteine, liberated from the tRNA, was modified with iodoacetic acid. The product was confirmed to be carboxymethyl-selenocysteine by two-dimensional TLC. Selenocysteyl-tRNA su should be used to synthesize glutathione peroxidase by co-translational mechanisms.
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