1. Allantoinase [EC 3.5.2.5] was isolated from cells of Candida utilis and unpurified by chromatography on columns of DEAE-cellulose and Sephadex G-200 after treatment with urea to remove urate oxidase [EC 1.7.3.3.]. 2. The purified allantoinase catalyzed the hydrolysis of allantoin into allantoic acid. However, only half of the allantoin produced from uric acid by urate oxidase was converted. The rest of the allantoin was unchanged, and showed a negative optical rotation. 3. On the other hand, the combined action of crude urate oxidase and allantoinase resulted in nearly complete conversion of uric acid into allantoic acid. Furthermore, the unpurified allantoinase preparation hydrolyzed racemic allantoin to allantoic acid completely. 4. These results indicate that the urate oxidase produces racemic allantoin from uric acid and that the allantoinase attacks only allantoin of positive optical rotation. The results also suggest that allantoin racemase is present in the yeast cells.

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