High taurine supplementation in plant protein-based diets improves growth and organoleptic characteristics of European seabass (Dicentrarchus labrax)

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PYRIDINE RIBOSIDASE FROM XANTHOMONAS PRUNI

Xanthomonas pruni is of considerable interest, since it appears to have a tryptophan-niacin in-terrelation similar to that in Neurospora crassa and mammals (Davis, Henderson, and Powell, 1951). This is in contrast to Escherichia coli and Bacillus subtilis, in which such interrelation is absent (Yanofsky, 1954). We found that the niacin requirement of X. pruni could be satisfied by diphosphopyridine nucleotide (DPN).3 This observation prompted the investigation of the metabolism of DPN by the organism. The final step in the degradation of DPN was found to be catalyzed by a pyridine ribosidase, which showed an unusual preference for the pyridine riboside linkage. Nucleoside splitting enzymes are abundant in nature. However, whether the enzymes are phos-phorolytic or hydrolytic, it appears always that both purine and pyridine ribosides are attacked. The enzyme from X. pruni is no exception, but the activity toward nicotinamide riboside, as compared to inosine, is far greater than has been encountered in other systems. MATERIALS AND METHODS Growth of organism. X. pruni was cultivated on nutrient agar slants with monthly transfers and grown in the slightly modified liquid culture medium (table 1) of Davis et al. (1951). Large scale cultures usually were initiated by inocula-tion with 0.1 volume of the same medium inocu-lated 2 days previously. Growth was continued for 60 hr at room temperature with vigorou