Characterization of the selenocysteine-containing metabolome in selenium-rich yeast

A critical evaluation of literature reports demonstrates the poor quality of analytical data on the presence and the concentration of selenocysteine ( SeCys) in yeast. The speciation of this amino acid was revisited by studying the behaviour of a well-defined mixture of selenocysteine-containing di- and tripeptides, isolated from yeast, during derivatisation and proteolytic digestion by 2D (size-exclusion-ion-pairing reversed-phase) HPLC-ICP-MS and electrospray MS/MS. Carbamidomethyl-selenocysteine was also synthesised, isolated by cation-exchange chromatography, characterised by electrospray Q-TOF MS/MS, and used for retention time matching. SeCys-containing oligopeptides showed a remarkable resistance to usual proteolytic digestion rendering the quantitative liberation of selenocysteine impossible. The quantification of this amino acid in yeast as the sum of Se-glutathione tripeptides ( till now the only family of SeCys-bearing species identified) was therefore recommended.