Synthesis of Selenocystine and Selenohomocystine with O-Acetylhomoserine Sulfhydrylase

We describe here the synthesis of selenium amino acids with O-acetylhomoserine sulfhydrylase, partially purified from baker’s yeast. The enzyme was found to catalyze the synthesis of l-selenocystine and l-selenohomocystine from Na₂Se₂ with the corresponding acetyl-derivatives of serine and homoserine, respectively. l-Serine-O-sulfate also serves as a substrate of the β-replacement reaction. Na₂Se₂ is less efficient as a substituent donor than the physiological substrate, NaHS, and inhibits the enzyme at high concentrations. Therefore, limited amounts of Na₂Se₂ were added to the reaction mixture to increase the yield (50 to 60%). This provides a facile method to produce optically active selenocystine and selenohomocystine.