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Query: EC:3.1.3.5 (5'-nucleotidase)
 3,167 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Intact cells of Bacillus cereus catalyze the breakdown of exogenous AMP to hypoxanthine and ribose 1-phosphate through the successive action of 5'-nucleotidase, adenosine deaminase, and inosine phosphorylase. Inosine hydrolase was not detectable, even in crude extracts. Inosine phosphorylase causes a "translocation" of the ribose moiety (as ribose 1-phosphate) inside the cell, while hypoxanthine remains external. Even though the equilibrium of the phosphorolytic reaction favors nucleoside synthesis, exogenous inosine (as well as adenosine and AMP) is almost quantitatively transformed into external hypoxanthine, since ribose 1-phosphate is readily metabolized inside the cell. Most likely, the translocated ribose 1-phosphate enters the sugar phosphate shunt, via its prior conversion into ribose 5-phosphate, thus supplying the energy required for the subsequent uptake of hypoxanthine in B. cereus.
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PMID:Utilization of exogenous purine compounds in Bacillus cereus. Translocation of the ribose moiety of inosine. 10 Apr 97

A model is proposed for the partial depletion of the adenine nucleotide pool in the ischemic perfused rat heart which involves seven enzymes: adenylate cyclase, 3',5'-cyclic AMP phosphodiesterase, 5'-nucleotidase, adenosine kinase, adenosine deaminase, purine nucleoside phosphorylase, and inorganic pyrophosphatase. The computer implementation of this model is in terms of rate laws, several of which were obtained by a systematic least-squares fitting procedure. Depletion of the adenine nucleotide pool is initiated by the release of endogenous noradrenaline into the interstitial fluid, which results from a fall in tissue PO2, and the subsequent activation of adenylate cyclase. In this model the substrate for 5'-nucleotidase is a membrane-bound AMP pool formed by hydrolysis of extracellular fluid and functions as a vasodilator; excess adenosine is incorporated into the tissue by a "permease" with Michaelis-Menten kinetics and converted to AMP, inosine, and hypoxanthine. Alternative mechanisms, such as the deamination of AMP by adenylate deaminase and conversion of AMP to adenine by AMP pyrophosphorylase, were rejected primarily on qualitative biochemical grounds.
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PMID:Computer simulation of ischemic rat heart purine metabolism. I. Model construction. 19 89

Inactivation of hypoxanthine phosphoribosyltransferase caused by periodate-oxidized GMP is irreversible, even under the conditions of polyacrylamide gel electrophoresis and during affinity chromatography on GMP-Sepharose. Partial binding of the inhibitor to the enzyme protein can be demonstrated on dodecyl sulfate gel electrophoresis: The substrate, phosphoribosyl diphosphate in the presence of Mg2, and the product GMP protect the enzyme against inactivation. Periodate-oxidized GMP, AMP and oxidized purine nucleosides do not influence ribosephosphate pyrophosphokinase, 5'-nucleotidase, purine-nucleoside phosphorylase and guanylate kinase. A variety of other purine nucleosides and nucleotides, tested in their periodateoxidized form, do not lead to a compound comparable or superior to oxidized GMP in its effect on hypoxanthine phosphoribosyltransferase. In an erythrocyte system it is clearly demonstrated that oxidized GMP cannot act across an intact cell membrane.
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PMID:Irreversible inhibition of hypoxanthine phosphoribosyltransferase. Further studies on the specificity of periodate-oxidized GMP. 20 May 44

The kinetic model of carbohydrate metabolism has been expanded to include: (a) the accumulation of alpha and beta-cellulose, insoluble cell-wall glycogen and mucopolysaccharide; (b) the role of RNA turnover as a source of carbon for end-product synthesis and as a buffer regulating the level of uridine nucleotides in this metabolic network; and (c) the role of purine-nucleoside phosphorylase, 5'-AMP nucleotidase, nucleosidediphosphate kinase and polynucleotide phosphorylase. One of many predictions based on this model is that cells differentiating in the presence of glucose will produce sorocarps with an abnormally high trehalose to cellulose ratio. External perturbation of either the model or of developing cells by glucose increases the levels of sorocarp trehalose and glycogen, 5-fold and 6-fold respectively. Evaluation of the experimental data and the simulation analyses have allowed several predictions to be made concerning the compartmentation of metabolites and the permeability of cells to glucose during differentiation.
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PMID:Fourth expansion and glucose perturbation of the Dictyostelium kinetic model. 55 94

Adult rat-liver epithelial cultures were sensitive to the lethal effects of 8-azaguanine (AG), but lines contained variants resistant to AG. The frequency of retrievable AG-resistant colonies varied with both the concentration of AG used and the seeding density of the population under selection. Cells resistant to AG were also cross-resistant to 6-thioguanine and unable to grow in medium containing hypoxanthine, aminopterin and thymidine. Resistance was stable. AG resistance was due to a deficiency of hypoxanthine-guanine phosphoribosyl transferase (HGPRTase) activity which was not caused by an inhibitor. In the assay for HGPRTase, a substantial amount of product appeared as inosine (In) in addition to inosine monophosphate (IMP). Purine nucleoside phosphorylase will generate In from hypoxanthine and, indeed, the cells did possess this activity. However, several findings indicated that the In was derived from IMP by catabolism by 5'-nucleotidase (NTase): (1) IMP decreased as In increased and (2) the inhibitors of NTase, adenosine monophosphate and thymidine triphosphate, reduced the generation of In by over 90% without inhibiting purine nucleoside phosphorylase. The cells possessed substantial NTase activity, 35% of which was located in the cytosol along with 69% of HGPRTase. Several lines of evidence suggested that the NTase activity limited the amount of 8-azaguanylic acid presented to the cells by catabolising the nucleotide and, thereby, reducing the toxicity of available AG.
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PMID:Characterization of analog resistance and purine metabolism of adult rat-liver epithelial cell 8-azaguanine-resistant mutants. 62 78

Xanthine oxidase, guanase, 5'-nucleotidase, and adenosine deaminase in human epidermis were demonstrated and accurately assayed with about 20 microng. of tissue by the new micro-assay methods which rely on the isolation of isotopically labeled end products from the substrates by electrophoresis on cellulose acetate membranes. These assay methods are rapid, reliable, and sensitive and are highly suitable for studies of small amount of human tissue. Theses methods for the separation of purine derivatives with cellulose acetate membrane will also permit the assays of purine nucleoside phosphorylase and nucleoside kinase.
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PMID:Simple micro-assay methods for enzymes of purine metabolism. 85 69

Biochemical changes in peritoneal macrophages and their relatedness to the cytostatic and phagocytotic function in C3HA mice injected with a single intraperitoneal dose of 0.45 mM carnosine and 4-methyluracil or stimulated with peptone have been studied. During the first 24 hours after injection both carnosine and 4-methyluracil increase the activity of adenosine deaminase and purine nucleoside phosphorylase, the key enzymes of purine catabolism which is the main source of O2-. radicals in macrophages. In carnosine-stimulated macrophages the activity of membrane 5'-AMP nucleotidase decreases on days 1-3 after injection which points to alleviation of adenosine-induced inhibition as well as to macrophage activation. Carnosine increases the cytostatic and phagocytotic activities of macrophage coupled to O2-. production. The mechanism of the stimulating effect of carnosine on macrophages seems to consist in the dipeptide interaction with specific receptors localized on the plasma membrane of macrophagal cells.
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PMID:[Carnosine as a stimulator of cytotoxic and phagocytic function of peritoneal macrophages]. 146 54

The metabolic fate of labeled hypoxanthine and inosine, degradation products of adenine nucleotides, was studied in cultured beating cardiomyocytes, in order to assess the physiological significance of their contribution to salvage nucleotide synthesis in the heart. Inosine and hypoxanthine were found to be incorporated into nucleotides by a similar rate, but in the presence of 8-aminoguanosine, a potent inhibitor of purine nucleoside phosphorylase (EC 2.4.2.1), the rate of inosine incorporation into nucleotides was markedly reduced (by 75%), indicating that inosine incorporation to IMP (inosinic acid) occurs following its degradation to hypoxanthine. The proportion of hypoxanthine converted to IMP by hypoxanthine-guanine phosphoribosyltransferase (EC 2.4.2.8) is markedly greater than that degraded to xanthine and uric acid by xanthine oxidase (EC 1.3.2.3). However, close to 50% of the IMP formed was degraded to inosine by IMP 5'-nucleotidase (EC 3.1.3.5). The results demonstrate the activity of the following futile cycle in the cardiomyocytes: hypoxanthine----IMP----inosine----hypoxanthine. The rational for the activity of this energy consuming cycle is yet unclear.
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PMID:Metabolic fate of hypoxanthine and inosine in cultured cardiomyocytes. 158 1

Adenosine produced from 5'-AMP has been proposed as a mediator of intrinsic renal regulation. The rates of 5'-AMP and adenosine metabolism are dependent on the activities of enzyme involved in purine metabolism. The activities of adenosine kinase (AK), adenosine deaminase (ADA), 5'-nucleotidase (5'-NT), AMP deaminase, xanthine oxidase and purine nucleoside phosphorylase were measured in cytosolic and membrane fractions from glomeruli, cortical tubules, medullary thick ascending limb of Henle (MTAL) and collecting duct prepared from rat kidney by combinations of sieving and sucrose density gradient centrifugation techniques. In the cytoplasm of glomeruli cells, the activity ratios of ADA/AK and AMP deaminase/5'-NT were 70 and 2.4, respectively. The highest activity of 5'-NT was found in membrane fractions of cortical tubules where it was equally distributed between luminal and antiluminal membranes. Membrane fractions of MTAL did not contain detectable amounts of adenosine deaminase activity. The highest activity of xanthine oxidase and purine nucleoside phosphorylase was in the cytoplasm fraction of glomeruli. These results suggest that deamination of AMP and adenosine may be favored in the cytoplasm of glomeruli cells. In contrast, in the extracellular space of glomeruli and especially in the cortical tubule, AMP can be converted preferentially to adenosine by 5'-NT.
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PMID:The distribution of enzymes involved in purine metabolism in rat kidney. 161 Aug 88

A pleiotropic mutation (cpm) which is localised in the vicinity of the spoA gene of Bacillus subtilis chromosome has been described. The mutation inhibits spore formation, renders bacteria auxotrophic for adenine and tyrosine, increases sensitivity to antibiotics, decreases cell motility and the ability to grow on D-ribose and D-xylose, inhibits growth of bacteriophages PBS1 and AR9 as well as enhances activity of alkaline proteinase and alpha-amylase. At the same time, the cpm mutants acquire the ability to produce inosine. Inosine excretion is connected with more than 50- and 5-fold increase in activity of 5'-nucleotidase in respect to IMP and AMP, accordingly, and 10-fold decrease in activity of purine nucleoside phosphorylase. Biosynthesis of inosine and Ade- phenotype of the cpm mutant are not mediated by the change in activity of sAMP synthetase. The nature and mechanism of action of the cpm mutation are under discussion.
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PMID:[A new pleiotropic mutation affecting purine metabolism, sporulation and biosynthesis of exoenzymes in Bacillus subtilis]. 177 39


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