Abstract
A coccolithopholid Emiliania huxleyi is a unicellular marine alga and requires selenium (Se) for its growth. In E. huxleyi, we previously reported six selenoproteins (EhSEP1~6) and among them, EhSEP2, is a novel protein disulfide isomerase containing Se. These phenomena suggest that E. huxleyi may possess unique selenoproteins. In this study, we characterized EhSEP1 to get new knowledge about physiological function of Se. After purification of EhSEP1, we determined partial amino acid sequences and cloned a full-length cDNA for EhSEP1. The deduced amino acid sequence of EhSEP1 had strong similarity to those of thioredoxin reductases (TR), which are well-characterized selenoproteins. The crude extracts of E. huxleyi exhibited significant TR activity, when Se was supplied into the culture media. However, levels of the EhSEP1 mRNA were constant despite amount of supply of Se. These results suggest that the translation of EhSEP1 might be responded to the levels of available Se.
