URIC ACID DEGRADATION AND BIOSYNTHESIS OF ENZYMES URICASE GLYOXYLATE CARBOLIGASE AND UREASE IN HYDROGENOMONAS H-16 .2. EFFECT OF URIC ACID FRUCTOSE AND NITROGEN DEFICIENCY ON ENZYME FORMATION

Changes in uricase, glyoxylate carboligase and urease activity were determined in fructose grown Hydrogenomonas H 16 cells during subsequent incubation with uric acid, allantoin and in nitrogen-deficient fructose media. The specific activities of uricase and glyoxylate carboligase increased within 2-3 hours up to levels of 35 and 1000 μmoles of substrate/min/g protein respectively, when the cells were transferred to an uric acid containing medium. These enzyme levels decreased after the substrate was consumed. Uric acid degradation was slightly stimulated by fructose, but was not affected by the addition of ammonia. In the presence of allantoin only glyoxylate carboligase was synthesized at a full rate, while uricase exhibited only a slight, temporary increase. Urea and ammonia were liberated from uric acid and accumulated in the suspension at a molar ratio of approximately 1:2. This ammonia formation was apparently not catalyzed by urease. Urease was not formed during growth with uric acid and allantoin, presumably due to the accumulation of ammonia. A pronounced synthesis of urease was observed under nitrogen deficiency, under which conditions uricase and glyoxylate carboligase were not formed. These data indicate, that urease, unlike other enzymes of the uric acid degrading pathway, is not induced by its substrate. It is considered, that urease formation in Hydrogenomonas H 16 is controlled by repression only, with ammonium ions serving as the repressing substrate. © 1969 Springer-Verlag.