PYRIMIDINE RIBONUCLEOSIDE CATABOLIC ENZYME-ACTIVITIES OF PSEUDOMONAS-PICKETTII

Pyrimidine ribonucleoside catabolic enzyme activities of the opportuni stic pathogen Pseudomonas pickettii were examined. Of the pyrimidine a nd related compounds tested, only dihydrouracil (nitrogen source) and ribose (carbon source) supported growth. Thin-layer chromatographic se paration of the uridine and cytidine catabolities produced by P. picke ttii extracts indicated that this pseudomonad contained nucleoside hyd rolase activity. Its presence was confirmed by enzyme assay. Hydrolase activity was elevated in both glucose- and ribose-grown cells relativ e to succinate-grown cells. Nucleoside hydrolase activity was depresse d when dihydrouracil served as a nitrogen source. Cytosine deaminase a ctivity was present in extracts prepared from succinate-, glucose- or ribose-grown cells when (NH4)(2)SO4 served as the nitrogen source alth ough cells grown on glucose or ribose exhibited a higher enzyme activi ty. Cytosine deaminase activity was not detected in extracts prepared from cells grown on dihydrouracil as a nitrogen source. Both dihydropy rimidine dehydrogenase and dihydropyrimidinase activities were measura ble in P. pickettii. The dehydrogenase activity was higher with NADH t han with NADPH as its nicotinamide cofactor when uracil served as its substrate. Carbon source did not affect dehydrogenase or dihydropyrimi dinase activity greatly but both activities were diminished in cells g rown on the nitrogen source dihydrouracil.