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Results for “Pyrimidine Nucleosides”

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At least 19 recordsLinked to original sources
PubMed1991

Production of 5-methyluridine by immobilized thermostable purine nucleoside phosphorylase and pyrimidine nucleoside phosphorylase from Bacillus stearothermophilus JTS 859.

5-Methyluridine was produced continuously from thymine and inosine by immobilized enzymes, which consisted of thermostable purine nucleoside phosphorylase and thermostable pyrimidine nucleoside phosphorylase obtained from Bacillus stearothermophilus JTS 859. The process was carried out in a column reactor at 60 degrees C for 17 d without any bacterial contamination under non-aseptical conditions. Half-lives of the activity of the immobilized enzymes were 47 d and 4.5 d at 60 degrees C and 70 degrees C, respectively, although half-life of the crude enzyme was only 14 h at 70 degrees C.

Bacterial Proteins↗
PubMed1975

Pyrimidine nucleoside analogues as inducers of pyrimidine nucleoside catabolizing enzymes in Salmonella typhimurium.

Various structural analogues of cytosine and uracil nucleosides were tested as potential inducers of the nucleoside catabolizing (cyt) enzymes in Salmonella typhimurium. Some analogues, e.g. 5'-O-alkyl cytidines and uridines, resistant to catabolic enzymes, were as effective as the natural inducers cytidine and uridine; but etherification of one of the cis 2' or 3'hydroxyls fully abolished activity, pointing to a requirement of an intact ribose cis-glycol system for activity. A uridine analogue in the syn conformation, 6-methyluridine, a good substrate for uridine phosphorylase, was inactive as an inducer. The behavior of various other analogues, in relation to their structure, conformation and substrate properties, indicated the absence of any correlation between inducing activity and substrate susceptibility. The overall findings are consistent with conclusions derived from genetic experiments. The active analogues apparently act via similar pathways, and probably affect the same regulatory mechanism(s) as the natural inducers.

Cytidine↗
PubMed1975

Phosphorylation of purine and pyrimidine nucleosides by isolated rat liver mitochondria.

Formation of 5'-AMP, 5'-GMP, 5'-CMP and 5'UMP was confirmed in isolated rat liver mitochondria incubated with alpha-ketoglutarate, inorganic phosphate, purine nucleoside and pyrimidine nucleoside. Increased incorporation of 32Pi into ATP, GTP and UTP was observed by adding purine- and pyrimidine nucleosides. The phosphorylation of nucleosides was inhibited severely by arsenite and affected slightly by the addition of nuclear or post-mitochondrial fraction.

Animals↗
PubMed1992

Sodium-dependent nucleoside transport in choroid plexus from rabbit. Evidence for a single transporter for purine and pyrimidine nucleosides.

The overall goal of this study was to determine the mechanisms by which nucleosides are transported in choroid plexus. Choroid plexus tissue slices obtained from rabbit brain were depleted of ATP with 2,4-dinitrophenol. Uridine and thymidine accumulated in the slices against a concentration gradient in the presence of an inwardly directed Na+ gradient. The Na(+)-driven uptake of uridine and thymidine was saturable with Km values of 18.1 +/- 2.0 and 13.0 +/- 2.3 microM and Vmax values of 5.5 +/- 0.3 and 1.0 +/- 0.2 nmol/g/s, respectively. Na(+)-driven uridine uptake was inhibited by naturally occurring ribo- and deoxyribonucleosides (adenosine, cytidine, and thymidine) but not by synthetic nucleoside analogs (dideoxyadenosine, dideoxycytidine, cytidine arabinoside, and 3'-azidothymidine). Both purine (guanosine, inosine, formycin B) and pyrimidine nucleosides (uridine and cytidine) were potent inhibitors of Na(+)-thymidine transport with IC50 values ranging between 5 and 23 microM. Formycin B competitively inhibited Na(+)-thymidine uptake and thymidine trans-stimulated formycin B uptake. These data suggest that both purine and pyrimidine nucleosides are substrates of the same system. The stoichiometric coupling ratios between Na+ and the nucleosides, guanosine, uridine, and thymidine, were 1.87 +/- 0.10, 1.99 +/- 0.35, and 2.07 +/- 0.09, respectively. The system differs from Na(+)-nucleoside co-transport systems in other tissues which are generally selective for either purine or pyrimidine nucleosides and which have stoichiometric ratios of 1. This study represents the first direct demonstration of a unique Na(+)-nucleoside co-transport system in choroid plexus.

Adenosine Triphosphate↗
PubMedDate not supplied

[Synthesis of purine and pyrimidine nucleosides under the action of high temperature and UV-radiation].

By means of UV-spectroscopy, gel filtration, thin layer and paper chromatography, it has been shown that the action of UV irradiation and heat on a dry mixture of nitrogenous bases and deoxyribose results in the formation of nucleoside pool, particulary deoxyadenosine. These energy sources were chosen in order to imitate at least approximately the conditions assumed to exist on the primitive Earth. Similar synthesis takes place in the atmosphere of the three gases studied, being more intensive in CO2 than in N2 or O2.

Deoxyribose↗
PubMed1979

Characterization of a mutant mouse lymphoma cell with deficient transport of purine and pyrimidine nucleosides.

A clone (AE1) of cells resistant to adenosine cytotoxicity was isolated from a mutagenized population of mouse T-lymphoma (S49) cells. These adenosine-resistant cells cannot transport adenosine or any other purine or pyrimidine nucleoside tested, but their transport of purine bases is intact. The AE1 cells also have an impaired ability to salvage thymidine. Kinetic analyses of the uptake of purine and pyrimidine nucleosides further substantiate the evidence that the facilitated transport of purine and pyrimidine nucleosides in S49 cells is mediated by the same carrier. Growth rate and transport studies indicate that the lack of expression of the nucleoside transport in AE1 cells is recessive in intraspecies cell-cell hybrids.

Animals↗
PubMed1992

Some novel pyrimidine nucleoside rearrangements effected by diethylaminosulfur trifluoride (DAST).

Pyrimidine nucleosides (or their 5'-aldehydes) when treated with DAST give O2,5'-(fluoro)-anhydronucleosides. If this is prevented by blocking N-3 or O4, the desired 5'-deoxy-5'-(di)-fluoronucleoside is accompanied by the production of a compound resulting from migration of the base following scission of the N-1-->C-1' bond and formation of O2-->C-5'. This is a particular example of a much more general phenomenon, seen when suitably substituted ribofuranoses are treated with DAST.

Diethylamines↗
PubMed1979

Kinetics and equilibria of pyrimidine nucleoside monophosphate kinase from human erythrocytes.

The common type of pyrimidine nucleoside monophosphate kinase (ATP:CMP phosphotransferase, EC 2.7.4.14), purified 50 000-fold from human erythrotes, reacted with a wide variety of nucleotides, but only ATP, dATP, UMP and CMP were good substrates. The optimum Mg2+ concentration, 2-3 mM, was generally independent of substrate concentration, of the nature of the substrate, and of the direction of the reaction. Kinetic studies indicated that a ternary complex was formed, that the substrates were bound at two unlike sites, and that the order of addition of substrates was random. Equilibrium constants were ATP + UMP 0.98, ATP + CMP 1.59, dATP + UMP 1.13, and ATP + AMP 1.20.

Adenosine Triphosphate↗
PubMed1976

Human erythrocyte pyrimidine nucleoside monophosphate kinase. Partial purification and properties of two allelic gene products.

Human pyrimidine nucleoside monophosphate kinase is a polymorphic enzyme having two allelic gene products, UMPK 1 and UMPK 2, in several populations. A procedure is described for the partial purification of this enzyme from human red blood cells resulting in a 1500-fold purification of the enzyme for UMPK 1 and 583-fold for UMPK 2. The purified enzyme preparation catalyzed the phosphorylation of UMP, CMP, and dCMP, and used ATP as the preferred phosphate donor. The heavy metals, mercury, and copper, were found to be strong inhibitors of pyrimidine nucleoside monophosphate kinase activity. EDTA was found to protect the enzyme from inactivation by the heavy metals, and 2-mercaptoethanol stabilized the enzyme during purification. UMPK 1 and UMPK 2 were found to have similar kinetic properties; however, UMPK 2 had a slower electrophoretic mobility and greater thermolability than UMPK 1.

Alleles↗
PubMed1976

Activation of rat liver pyrimidine nucleoside monophosphate kinase.

The activity of the pyrimidine nucleoside monophosphate kinase (ATP:dCMP phosphotransferase, EC 2.7.4.14) from rat liver is dependent upon the presence of sulfhydryl-reducing agents. Addition to the inactive enzyme of 2-mercaptoethanol (5 mM), a reagent specific for cleavage of disulfide bonds, effects a reduction in molecular weight from approx. 53 000 to 17 000, measured by molecular sieve chromatography. This low molecular weight form is partially active in the presence of 2-mercaptoethanol (f mM). In absence of 2-mercaptoethanol, the low molecular weight form is inactive. Higher concentrations of 2-mercaptoethanol (50 mM) fully reactivate the CMP(ATP) kinase activity followed by dCMP(ATP) and CMP(dCTP) kinase activities in a sequential manner, without further change in moelcular weight. Alkylation by iodoacetamide of the enzyme at different stages of reactivation in dithiothreitol suggests an ordered appearance of the various enzyme activities. Furthermore, iodoacetamide inactivates the fully active enzyme. Thioredoxin was found to activate the enzyme in a manner similar to 2-mercaptoethanol and dithiothreitol. These results are consistent with the interpretation that the mechanism of activation of the enzyme involves cleavage of inter- and intramolecular disulfide bonds.

Adenosine Triphosphate↗
PubMed1975

A pyrimidine nucleoside monophosphate kinase from rat liver.

A pyrimidine nucleoside monophosphate kinase has been purified 2100-fold from rat liver. With ATP and dATP as phosphate donors the kinase uses CMP, dCMP, and UMP as phosphate acceptors. Ara-CMP is also phosphorylated by the kinase. In contrast to dCMP and UMP, CMP can be phosphorylated by dCTP. CTP and ara-CTP cannot substitute for dCTP. The stringent specificity of the phosphate donor site for ATP and dATP is lost when CMP serves as acceptor. All nucleoside triphosphates act as donors to a significant extent. No evidence has been found to suggest more than one enzyme. All activities, to different degrees, are strictly dependent upon preincubation at 37 degrees with a sulfhydryl reducing agent. Various reagents (85 mM) are ranked in order of increasing effectiveness of reactivation as follows: dithiothretiol greater than glutathione larger than or equal to 2-mercaptoethanol greater than L-cysteine greater than DL-alpha-lipoic acid. A NADP+-dependent thioredoxin (17 muM)-thioredoxin reductase system from Novikoff ascites rat tumor was found to be the most powerful reducing agent tested. CTP, dCTP, UTP, and dTTP (1 mM) do not affect the kinase activity regardless of the phosphate acceptor.

Animals↗