Cyclic amidohydrolases, including hydantoinase, dihydropyrimidinase, allantoinase, and dihydroorotase, are involved in the metabolism of pyrimidines and purines, sharing the property of hydrolyzing the cyclic amide bond of each substrate to the corresponding N-carbamyl amino acids. Allantoinases catalyze the degradation of purines, while dihydropyrimidinases and hydantoinases, a microbial counterpart of dihydropyrimidinase, are involved in pyrimidine degradation. Dihydroorotase participates in the de novo synthesis of pyrimidines.
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