β-Selenaproline as competitive inhibitor of proline activation

Abstract β-Selenaproline, a proline analog having the β-methylene group substituted by a selenium atom, has been tested in ATP-PP i exchange reaction catalyzed by either Escherichia coli or rat liver aminoacyl-tRNA synthetases. It has been shown that with both enzymatic systems β-selenaproline does not give rise to ATP-PP i exchange, but specifically inhibits proline activation. The inhibition is of fully competitive type and the K i values, lower than the K m values for proline, show that β-selenaproline binds to the synthetases with high affinity. The inability to form the complex with AMP, taking into account also the behavior of γ-selenaproline and other proline analogs, has been ascribed to the presence of the selenium atom in the β-position.