Involved in the asymmetric conversion of racemic 5-substituted hydantoins to the corresponding L-amino acids. Catalyzes the racemization via enolization of D- and L-5-monosubstituted hydantoins. It shows preference for hydantoins with arylalkyl side chains such as 5-benzyl-hydantoin (BH) and 5-(3-indolymethylene)-hydantoin (IMH). a D-5-monosubstituted hydantoin = a L-5-monosubstituted hydantoin Completely inhibited by HgCl(2) and iodoacetamide. Stimulated by dithiothreitol. Optimum pH is 8.5. Optimum temperature is 55 degrees Celsius. Homohexamer, homoheptamer or homooctamer. Belongs to the HyuE racemase family.