O-ureidoserine racemase (DcsC) is a PLP-independent racemase involved in the biosynthesis of the important antibiotic D-cycloserine. Our goal is to elucidate the mechanism of this unusual epimerization by means of crystallization of the enzyme with a known optically pure inhibitor. Alternatively, the mechanistic information can be achieved by crystallization of the racemic inhibitor with site-specifically mutated DcsC variants. This approach has been shown successfully in proving the proposed epimerization mechanism for the highly homologous diaminopimelate epimerase. With a crystal structure in hand we will be able to visualize the 3D geometry of the active site revealing how DcsC is able to significantly decrease the pka of the substrate thus enabling the proton abstraction under physiological conditions.