IUBMB Enzyme Nomenclature


Accepted name: hydantoin racemase

Reaction: D-5-monosubstituted hydantoin = L-5-monosubstituted hydantoin

Glossary: hydantoin = imidazolidine-2,4-dione

Other name(s): 5'-monosubstituted-hydantoin racemase; HyuA; HyuE

Systematic name: D-5-monosubstituted-hydantoin racemase

Comments: This enzyme, along with N-carbamoylase (EC and EC and hydantoinase, forms part of the reaction cascade known as the "hydantoinase process", which allows the total conversion of D,L-5-monosubstituted hydantoins into optically pure D- or L-amino acids [7]. The enzyme from Pseudomonas sp. (HyuE) has a preference for hydantoins with aliphatic substituents, e.g. D- and L-5-(2-methylthioethyl)hydantoin, whereas that from Arthrobacter aurescens shows highest activity with arylalkyl substituents, especially 5-benzylhydantoin, at the 5-position [2]. In the enzyme from Sinorhizobium meliloti, Cys76 is responsible for recognition and proton retrieval of D-isomers, while Cys181 is responsible for L-isomer recognition and racemization [6].

Links to other databases: BRENDA, EXPASY, KEGG, Metacyc, CAS registry number:


1. Watabe, K., Ishikawa, T., Mukohara, Y. and Nakamura, H. Purification and characterization of the hydantoin racemase of Pseudomonas sp. strain NS671 expressed in Escherichia coli. J. Bacteriol. 174 (1992) 7989-7995. [PMID: 1459947]

2. Wiese, A., Pietzsch, M., Syldatk, C., Mattes, R. and Altenbuchner, J. Hydantoin racemase from Arthrobacter aurescens DSM 3747: heterologous expression, purification and characterization. J. Biotechnol. 80 (2000) 217-230. [PMID: 10949312]

3. Martínez-Rodríguez, S., Las Heras-Vázquez, F.J., Mingorance-Cazorla, L., Clemente-Jiménez, J.M. and Rodríguez-Vico, F. Molecular cloning, purification, and biochemical characterization of hydantoin racemase from the legume symbiont Sinorhizobium meliloti CECT 4114. Appl. Environ. Microbiol. 70 (2004) 625-630. [PMID: 14711700]

4. Martínez-Rodríguez, S., Las Heras-Vázquez, F.J., Clemente-Jiménez, J.M. and Rodríguez-Vico, F. Biochemical characterization of a novel hydantoin racemase from Agrobacterium tumefaciens C58. Biochimie 86 (2004) 77-81. [PMID: 15016445]

5. Suzuki, S., Onishi, N. and Yokozeki, K. Purification and characterization of hydantoin racemase from Microbacterium liquefaciens AJ 3912. Biosci. Biotechnol. Biochem. 69 (2005) 530-536. [PMID: 15784981]

6. Martínez-Rodríguez, S., Andújar-Sánchez, M., Neira, J.L., Clemente-Jiménez, J.M., Jara-Pérez, V., Rodríguez-Vico, F. and Las Heras-Vázquez, F.J. Site-directed mutagenesis indicates an important role of cysteines 76 and 181 in the catalysis of hydantoin racemase from Sinorhizobium meliloti. Protein Sci. 15 (2006) 2729-2738. [PMID: 17132860]

7. Altenbuchner, J., Siemann-Herzberg, M. and Syldatk, C. Hydantoinases and related enzymes as biocatalysts for the synthesis of unnatural chiral amino acids. Curr. Opin. Biotechnol. 12 (2001) 559-563. [PMID: 11849938]

[EC created 2008]

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