D-hydantoinases (D-HYD) also called dihydropyrimidases (DHPase) and related proteins; DHPases are a family of enzymes that catalyze the reversible hydrolytic ring opening of the amide bond in five- or six-membered cyclic diamides, like dihydropyrimidine or hydantoin. The hydrolysis of dihydropyrimidines is the second step of reductive catabolism of pyrimidines in human. The hydrolysis of 5-substituted hydantoins in microorganisms leads to enantiomerically pure N-carbamyl amino acids, which are used for the production of antibiotics, peptide hormones, pyrethroids, and pesticides. HYDs are classified depending on their stereoselectivity. This family also includes collapsin response regulators (CRMPs), cytosolic proteins involved in neuronal differentiation and axonal guidance which have strong homology to DHPases, but lack most of the active site residues.