DEGRADATION OF PYRIMIDINE NUCLEOTIDES BY ENZYME SYSTEMS OF STREPTOMYCES

Abstract

Pyrimidine 5[image]-nucleotide phosphoribo-(deoxyribo)-hydrolase which hydrolyzes the N-glycosidic linkage in pyrimidine 5[image]-nucleotides to pyrimidine bases and pentose-5-phosphates was extracted and purified to about 31-fold from the cells of S. virginiae, and its properties examined. The purified enzyme hydrolyzed 5 -UMP, 5[image]-CMP, 5[image]-d UMP, 5[image]-d TMP and 5[image]-d CMP. Purine 5[image]-nucleotides were degraded by the crude extracts, but this activity was removed by the purification. Nucleosides and 3[image]-nucleotides of purines and pyrimidines were never cleaved even by the crude extracts. 2[image]-O-methyl-5[image]-UMP was resistant to the enzyme reaction. The Km value for 5[image]-UMP was 6.95 x 10-6 M. Co-factors of low molecular weight were unnecessary for the reaction. Phosphate, pyrophosphate and ATP had little stimulatory effect on the reaction. The enzyme was relatively heat stable between pH 5.5 and 8.8. The activity remained unaffected after heating the enzyme solution at 65[degree] for 45 min; Ca++ markedly stabilized the enzyme.