D-Selenocystine α, β-Lyase of Clostridium Sticklandii

Abstract

We have found a novel enzyme that catalyzes α, β-elimination of D-selenocystine to produce pyruvate, ammonia and elemental selenium in Clostridium sticklandii cells, and named it D-selenocystine α, β-lyase. The enzyme purified to homogeneity from C. sticklandii has a molecular weight of about 74,000, and consists of two subunits identical in molecular weight (35,000). The enzyme requires pyridoxal 5'-phosphate as a coenzyme. In addition to D-selenocystine, D-cystine, D-lanthionine, mesolanthionine, and D-cysteine serve as substrate, but D-selenocysteine is inert. D-Selenocystine α, β-lyase catalyzes also β-replacement reaction between D-selenocystine and various thiols to produce the corresponding S-substituted D-cysteines. Selenols also act as substituent donors for D-cystine to produce Se-substituted D-selenocysteines.