Selenalysine as substrate of lysine decarboxylase

Selenalysine, a lysine analog having the C4 methylene group substituted by a selenium atom, may be decarboxylated to selenolanthionamine by bacterial lysine decarboxylase. The kinetic parameters obtained studying comparatively the decarboxylation of lysine, thialysine and selenalysine showed that while the enzyme is more effective on lysine than on its two analogs, there are no great differences between the last two. These results indicate that the substrate specificity of lysine decarboxylase is greatly affected by the substitution of a carbon atom of the substrate molecule, but the presence of either sulfur or selenium as eteroatom is without appreciable effect on the binding of the lysine analogs to the enzyme. In other words either sulfur- or selenium-containing substrate analogs are acted upon in the same way by lysine decarboxylase.