Pyrimidine ribonucleoside catabolic enzyme activities of Pseudomonas pickettii

Ribonucleoside Hydrolases-Structure, Functions, Physiological Role and Practical Uses

Ribonucleoside hydrolases are enzymes that catalyze the cleavage of ribonucleosides to nitrogenous bases and ribose. These enzymes are found in many organisms: bacteria, archaea, protozoa, metazoans, yeasts, fungi and plants. Despite the simple reaction catalyzed by these enzymes, their physiological role in most organisms remains unclear. In this review, we compare the structure, kinetic parameters, physiological role, and potential applications of different types of ribonucleoside hydrolases discovered and isolated from different organisms.

Escherichia coli dihydropyrimidine dehydrogenase is a novel NAD-dependent heterotetramer essential for the production of 5,6-dihydrouracil

The reductive pyrimidine catabolic pathway is absent in Escherichia coli. However, the bacterium contains an enzyme homologous to mammalian dihydropyrimidine dehydrogenase. Here, we show that E. coli dihydropyrimidine dehydrogenase is the first member of a novel NADH-dependent subclass of iron-sulfur flavoenzymes catalyzing the conversion of uracil to 5,6-dihydrouracil in vivo.

A gene cluster involved in pyrimidine reductive catabolism from Brevibacillus agri NCHU1002

Genes involved in pyrimidine reductive catabolism (pyd) were isolated from a moderate thermophile, Brevibacillus agri NCHU1002, and nine ORFs in an 8.2-kb DNA fragment were identified by DNA sequence analysis. The pyd gene cluster included three closely spaced ORFs, designated pydA, pydB, and pydC, transcribed in the same orientation. Based on their amino acid sequence identity and enzyme activity assay, the gene products were identified as dihydropyrimidine dehydrogenase (PydA), dihydropyrimidinase (PydB), and beta-alanine synthase (PydC). Northern blot and primer extension analyses revealed that the pydBC genes are induced by dihydrouracil and regulated under the control of sigma(54) recognized promoter at transcriptional level as a polycistronic operon. All results indicate that the pydABC genes participate in the pathway of the pyrimidine reductive catabolism. This is the first bacterial pyd gene cluster to be reported.

Degradation of pyrimidine ribonucleosides by Pseudomonas aeruginosa

Pyrimidine ribonucleoside degradation in the human pathogen Pseudomonas aeruginosa ATCC 15692 was investigated. Either uracil, cytosine, 5-methylcytosine, thymine, uridine or cytidine supported P. aeruginosa growth as a nitrogen source when glucose served as the carbon source. Using thin-layer chromatographic analysis, the enzymes nucleoside hydrolase and cytosine deaminase were shown to be active in ATCC 15692. Compared to (NH4)2SO4-grown cells, nucleoside hydrolase activity in ATCC 15692 approximately doubled after growth on 5-methylcytosine as a nitrogen source while its cytosine deaminase activity increased several-fold after growth on the pyrimidine bases and ribonucleosides examined as nitrogen sources. Regulation at the level of protein synthesis by 5-methylcytosine was indicated for nucleoside hydrolase and cytosine deaminase in P. aeruginosa.