DEGRADATION OF PYRIMIDINE NUCLEOTIDES BY ENZYME SYSTEMS OF STREPTOMYCES

[摘要] A novel enzyme, pyrimidine 5′-nucleotide phosphoribo (deoxyribo) hydrolase, which hydrolyzes the N-glycosidic linkage in pyrimidine 5′- ucleotides to pyrimidine bases and pentose-5-phosphates, was extracted and purified to about 31-fold from the cells of Streptomyces virginiae and its properties were examined.The purified enzyme hydrolyzed 5′-UMP, 5′-CMP, 5′-deoxyUMP, 5′- deoxyTMP and 5′-deoxyCMP. Purine 5′-nucleotides were degraded by the crude extracts, but this activity was removed by the purification. Nucleosides and 3′-nucleotides of purines and pyrimidines were never cleaved even by the crude extracts. 2′-O-methyl-5′-UMP was also resistant to the enzyme reaction.The Km value for 5′-UMP was 6.95×10-3M. 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 activityremained unaffected after heating the enzyme solution at 65° for 45min. Ca++ had a marked stabilizing effect on the enzyme.

[学科分类] 微生物学和免疫学