Information on EC 5.1.99.5 - hydantoin racemase

This enzyme, along with N-carbamoylase (EC 3.5.1.77 and EC 3.5.1.87) 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 . The enzyme from Pseudomonas sp. (HyuE) has a preference for hydantoins with aliphatic substituents, e.g. D- and L-5-[2-(methylsulfanyl)ethyl]hydantoin, whereas that from Arthrobacter aurescens shows highest activity with arylalkyl substituents, especially 5-benzylhydantoin, at the 5-position . 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 .