In enzymology, a carboxymethylhydantoinase (EC 3.5.2.4) is an enzyme that catalyzes the chemical reaction

L-5-carboxymethylhydantoin + H₂O N-carbamoyl-L-aspartate

Thus, the two substrates of this enzyme are L-5-carboxymethylhydantoin and H₂O, whereas its product is N-carbamoyl-L-aspartate.

This enzyme belongs to the family of hydrolases, those acting on carbon-nitrogen bonds other than peptide bonds, specifically in cyclic amides. The systematic name of this enzyme class is L-5-carboxymethylhydantoin amidohydrolase. This enzyme is also called hydantoin hydrolase.

• LIEBERMAN I, KORNBERG A (1954). "Enzymatic synthesis and breakdown of a pyrimidine, orotic acid. I Dihydroortic acid, ureidosuccinic acid, and 5-carboxymethylhydantoin". J. Biol. Chem. 207 (2): 911–24. PMID 13163076.