Pyrimidine nucleoside catabolism in penicillium chrysoyenum

ABSTRACT

P. Chrysogenum utilized cytidine recognized as the sole source of nitrogen. This pyrimidine nucleoside supported the good growth of P. chrysogenum compared to that obtained with sodium nitrate. Dailyzed cell-free extracts of this organism hydrolyzed cytidine and uridine to the correspondings base and ribose by the pyrimidine nucleoside hydrolase. Pyrimidine nucleoside hydrolase was found to be constitutive. It was proved experimentally that this enzyme had hydrological activity and no phosphorylation occurred. Thymidine can not be cleaved under these experimental conditions. The pH optimum for cytidine and uridine hydrolysis was the same 6.2, and the optimum temperature was found to be 40C. It has been proved that pyrimidine nucleoside hydrolase differs from the purine nucleoside hydrolase in the same organism. The Km value of the enzyme was calculated and fond to be 13.5 x 10-3 M for cytidine and 16.6 x 10-3 M for uridine