CHROMATOGRAPHIC SEPARATION OF ISOLOGOUS SULFUR- AND SELENIUM-CONTAINING AMINO ACIDS - REDUCTIVE SCISSION OF SELENIUM-SELENIUM BOND BY MERCAPTANS AND SELENOLS

Racemic Se-methylselenocysteine, selenocystine, selenomethionine, selenoethionine, and Se-benzylselenocysteine are separated from their corresponding sulfur isologs by ion-exchange chromatography. The reason was uncovered for previous failures to obtain reproducible color values for selenocystine. The selenium-selenium bond of selenocystine is cleaved by mercaptans and selenols, yielding acyclic molecules with selenium-sulfur or selenium-selenium bonds. The diselenide-sulfhydryl and diselenide-selenol interchange reactions, which occur over a wide pH range, must be taken into account during analytical investigations involving mixtures of diselenides, and/or thiols, and/or selenols. Treatment of peptides containing selenocystine or selenocysteine residues (1-selenooxytocin, 6-selenooxytocin, deamino-1-selenooxytocin, deamino-6-selenooxytocin and deaminodiselenooxytocin) in 6 N HCl at 110° for 22 hr partially degraded selenocystine; however, when selenocystine itself was treated under identical reaction conditions it was almost entirely destroyed. © 1969.