The structure of the {:I-galactosidase inhibitor, galactostatin, isolated from Streptomyces Iydicus PA-5726 was determined to be 5-amino-5-deoxygalactopyranose, in which the ring oxygen of galactose has been replaced by nitrogen. For this study, two derivatives of galactostatin were prepared by oxidation and reduction, respectively. The oxidation product of galactostatin was 5amino-5-deoxygalactonic-b-Iactam (galactostatin-Iactam) and the reduction product was 5-amino-1,5-dideoxygalactopyranose (I-deoxygalactostatin).

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Galactostatin obtained from the fermenta,tion broth of Streptomyces lydicus PA-5726 strongly inhibited fJ-galactosidase. Its derivatives, galactostatin-lactam and I-deoxygalactostatin, were also inhibitors. Galactostatin and I-deoxygalactostatin were fully competitive inhibitors with high affinities for Penicillium multicolor fJ-galactosidase, and their Ki values were 4.0 x 10-9 and 3.3 x 10-8 M at pH 6.0, respectively, using ONPG as substrate. In their presence, the steady-state velocities of the enzyme were reached in a matter of minutes. Galactostatin-Iactam, in contrast, showed no detectable lag time on interaction with the enzyme, and the type of inhibition was also competitive with a Ki value of 1.3 x 10-5 M. These three inhibitors bound to the enzyme in the same molar ratio (1 : 1).1649

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.