Dihydropyrimidinase catalyzes the reversible hydrolytic ring opening of dihydrouracil and dihydrothymine to N-carbamoyl-beta-alanine and N-carbamyl-beta-aminoisobutyrate, respectively. Dihydropyrimidinase from microorganisms is normally known as hydantoinase because of its role as a biocatalyst in the synthesis of D- and L-amino acids for the industrial production of antibiotic precursors and its broad substrate specificity. Dihydropyrimidinase belongs to the cyclic amidohydrolase family, which also includes imidase, allantoinase, and dihydroorotase. Although these metal-dependent enzymes share low levels of amino acid sequence homology, they possess similar active site architectures and may use a similar mechanism for catalysis. By contrast, the five human dihydropyrimidinase-related proteins possess high amino acid sequence identity and are structurally homologous to dihydropyrimidinase, but they are neuronal proteins with no dihydropyrimidinase activity. In this chapter, we summarize and discuss current knowledge and the recent advances on the structure, catalytic mechanism, and inhibition of dihydropyrimidinase.
