Involved in the biosynthesis of the antibiotic D-cycloserine (DCS), a cyclic structural analog of D-alanine, used as an antitubercular agent. Catalyzes the stereoinversion of O-ureido-L-serine to O-ureido-D-serine. O-ureido-L-serine = O-ureido-D-serine Inhibited by thiol-inactivating reagents such as iodoacetamide and Hg(2+) ions. kcat is 158 sec(-1) and 29 sec(-1) for O-ureido-L-serine and O-ureido-D-serine, respectively (at 30 degrees Celsius). Optimum pH is 7.9. Monomer. It employs a two-base mechanism, with a thiolate-thiol pair in the active site. Belongs to the diaminopimelate epimerase family.