Identification of Selenocysteine in the Proteins of Selenate-grown Vigna radiata

Abstract

Selenocysteine, the S analog of cysteine, was identified in proteins of V. radiata (L.) Wilczak grown with selenate. To stabilize selenocysteine and prevent its breakdown, the carboxymethyl derivative was synthesized by the addition of iodoacetic acid to the protein extract from [75Se]selenate-grown plants. A 75Se-labeled component of the carboxymethylated protein hydrolysate possessed chromatographic properties identical to those of a 14C-labeled carboxymethylselenocysteine standard during paper and TLC and during gel-exclusion, anion-exchange and cation-exchange column chromatography. Detection of selenocysteine in proteins of a selenium-sensitive plant, and the possibility that the presence of this compound alters normal functions, provides an explanation for the toxic effects of Se.