Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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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)

1. Enzymes interconnecting the adenylate pool were present in high concentration. 2. AMP and adenosine were easily deaminated by the corresponding enzymes whose high levels were detected. 3. Adenylate was hydrolyzed either by deamination to yield IMP which was further dephosphorylated to inosine or by dephosphorylation to adenosine followed by deamination to inosine. 4. Incubation of gill extract with [-14C]-AMP in the presence and absence of ATP but with adenosine deaminase inhibitors allowed demonstration that ATP controlled the balance between these pathways. 5. Some biochemical properties of 5'-nucleotidase. AMP deaminase and adenosine deaminase were defined. 6. Purine salvage enzymes were also estimated.
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PMID:Aspects of purine metabolism in the gill epithelium of rainbow trout, Salmo gairdneri Richardson. 31 37

Mutants in which the expression of periplasmic enzymes by whole cells is reduced (termed "cryptic") are also found to show greatly reduced uptake of labeled adenosine 5'-monophosphate (5'-AMP), providing a rapid assay for crypticity. The crypticity of 3'- and 5'-nucleotidase has been examined as a function of substrate concentration. The Km for 3'- or 5'-AMP increases in the cryptic mutants when whole cells are used as the enzyme source. The Vmax is not altered. Electrophoretic analysis of protein prepared from cell envelopes showed that three cryptic mutants have a polypeptide absent from the outer membrane and a relatively high proportion of a polypeptide in the inner membrane. Analysis of the molar ratios of constituent sugars of the lipopolysaccharides showed no differences between three cryptic mutants and the parent strain. One cryptic mutant (3--41), however, has altered sensitivity to phage T4. By selection for phage resistance, derivatives of the cryptic mutants that are deoxycholate sensitive have been obtained. These mutants are no longer cryptic. We suggest that cryptic mutants have an altered outer membrane, with decreased permeability to 3'- and 5'-AMP, as a result of an altered polypeptide.
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PMID:Mutants of Escherichia coli "cryptic" for certain periplasmic enzymes: evidence for an alteration of the outer membrane. 32 Jan 75

Suspensions of endocrine pancreas cells were prepared by shaking collagenase-isolated rat islets of Langerhans in calcium-free buffer. When incubated with 1.0 mM substrate at pH 7.4, the cells split Pi from 5'-AMP at a rate of 87 nmol/h per microgram DNA, and from beta-glycerophosphate at a rate of 25 nmol/h per microgram DNA. Km for 5'-AMP was about 54 microM. Adenosine or theophylline inhibited the 5'-AMP hydrolysis. Homogenization of the cells increased the activity toward 5'-AMP by 23% and that toward beta-glycerophosphate by 115%. Injecting rats with cortisone had no effect on the 5'-AMP hydrolysis by whole cells but significantly increased the activity in cell homogenates; the intracellular activity toward 5'-AMP was more than doubled by the cortisone treatment. Staining whole islet cells for 5'-AMP-splitting activity resulted in a demarcation of the cell periphery in control rats. Cells from cortisone-treated rats showed heavier deposits of reaction product, and their cell periphery did not stand out as clearly. It is suggested that 5'-nucleotidase is largely an ectoenzyme in normal rat islet cells. The cells also contain an as yet unidentified intracellular phosphatase that seems to be solely responsible for the increased hydrolysis of 5'-AMP in cortisone-treated rats.
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PMID:5'-AMP hydrolysis by suspensions and homogenates of pancreatic islet cells from normal and cortisone-treated rats. 38 76

Oncogenic cultured rat C6 astroblastoma cells display strikingly high ecto-5'-adenosine monophosphatase (ecto-5'-AMPase) activity, 4.23 +/- 20 mumol of Pi liberated by intact cells from 3 mM extracellular 5'-AMP (mg of protein-1 h-1, as compared with 0.15 +/- 0.01 for nononcogenic cultured hamster astroblasts. A further rise in C6 cell ecto-5'-AMPase activity occurs with increase in cell density during growth. Less than 2 pg of the lectin, concanavalin A (Con A), bound per cell reversibly inhibits most of the cellular ecto-5'-AMPase activity. Inhibition by Con A binding is independent of cellular temperature. Con A binding suppresses phosphohydrolase activity of a pK=7.4 functional group on the cell surface. A direct proportionality is observed between quantity of Con A bound to the cell surface and simultaneous relative decreases both in Michaelis constant and maximum velocity of ecto-5'-AMPase in the intact cell. The findings suggest that a major consequence of the specific high affinity binding of Con A to the C6 cell surface is the inactivation of the enzyme--substrate complex of ecto-5'-AMPase.
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PMID:Effect of concanavalin A on the kinetics of ecto-5'-adenosine monophosphatase (5'-adenosine monophosphate phosphohydrolase) in the outer surface of intact neural cells in culture. 42 Jul 87

Adenine nucleotide breakdown to nucleosides and purine bases was measured in cultures of human lymphoblastoid cells following: 1) the inhibition of oxidative phosphorylation in the absence of glucose or 2) the addition of 2-deoxyglucose. A mutant cell line, deficient in adenosine kinase, in the presence of an adenosine deaminase inhibitor was used to measure utilization of the two pathways of AMP catabolism involving initial action of either purine 5'-nucleotidase or AMP deaminase. In such a system the appearance of adenosine induced by the oxidative phosphorylation inhibitor, rotenone, implies that approximately 70% of AMP breakdown occurs via dephosphorylation. By the same method, deamination accounts for 82% of AMP breakdown when 2-deoxyglucose is added. The occurrence of AMP dephosphorylation is not correlated with elevated concentrations of substrate or with decreased concentrations of the inhibitors of 5'-nucleotidase, ATP and ADP. Dephosphorylation occurs if, and only if, the adenylate energy charge decreases to about 0.6 in these experiments. In cultures deprived of glucose and oxygen, adenine nucleotide degradation via dephosphorylation results in recovery of normal energy charge values.
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PMID:Adenine nucleotide degradation during energy depletion in human lymphoblasts. Adenosine accumulation and adenylate energy charge correlation. 47 72

The characteristics of 5'-nucleotidase in a clonal line (C6) of rat glioma cells has been examined in detail. The cells liberated 6.80 +/- 0.33 mumol of inorganic phosphate/mg of cell protein/hour, producing nearly equimolar amounts of adenosine and inorganic phosphate from AMP in the extracellular fluid. No 5'-nucleotidase was released by the cells into the medium. Most of the 5'-nucleotidase activity was found to be located in the outer surface of the plasma membrane of C6 cells and rapidly accessible to exogenous AMP, by experiments based upon differential labeling of extracellular and intracellular compartments with 32P and 33P. The ecto-enzyme was active in the absence of divalent cations. However, Mn2+ or Co2+ were somewhat stimulatory. Zn2+ suppressed activity very markedly. The relationship of enzymatic reaction velocity to pH was complex, with an optimum at pH 7.4 for all substrates tested. The ecto-5'-nucleotidase readily hydrolyzed 5'-AMP and 5'-UMP. Other 5'-nucleoside monophosphates, including 5'-deoxy-AMP, were also hydrolyzed, but more slowly; 2'- or 3'-nucleoside monophosphates were not attacked. The ecto-5'-nucleotidase in the intact cell obeyed Michaelis-Menten kinetics. Apparent Km for AMP was 0.22 mM; apparent Km values for other substrates were similar and ranged from 0.16 to 0.18 mM. ADP exerted a very powerful inhibitory effect, behaving as a competitive inhibitor, and 5'-UMP behaved as a strictly competitive substrate for 5'-AMP. ATP and ITP were inhibitory. Of these, ITP served to increase Km for AMP. ATP did likewise, but also greatly lowered Vmax. These findings indicate that the intact cell is capable of rapid hydrolysis of exogenous 5'-AMP, to produce adenosine at the cell surface at a rate which responds directly to extracellular AMP concentration but which can be suppressed by extracellular ADP or ATP.
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PMID:Ecto-5'-nucleotidase of intact cultured C6 rat glioma cells. 81 33

The treatment of plasma membranes by a French pressure cell in sucrose medium devoid of detergents solubilized 20% of the total protein and 95--100% of 5'-nucleotidase activity. The soluble enzyme was 40--90-fold purified by centrifugation in a sucrose gradient with a 10--20% yield with respect to the orginal lysate. The purified fraction retained the same high specificity for 5'-AMP (Km = 20 micron) as in the plasma membranes and was enriched in sphingomyelin. Whereas 5'-AMP at high concentration inhibited the membrane-bound enzyme, it had no effect on the solubilized form. The soluble enzyme was stimulated by 2 X 10(-13)-2 X 10(-15) g concanavalin A without any inhibition with higher doses of lectin. The plasma-membrane bound stimulated and inhibited 5'-nucleotidase was modulated by concanavalin A concentrations higher than 0.1 microgram. Inhibition of the activity of the soluble enzyme by antiphosphorylcholine antibodies was not observed with membranes. The regulation of 5'-nucleotidase acitvity in plasma membranes might be associated with a supramolecular organization.
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PMID:Differences in the modulations of the soluble of plasma-membrane-bound 5'-nucleotidase. 92 72

Adenosine 5'-monophosphate is dephosphorylated before its uptake by cells of Escherichia coli. This is demonstrated by using a radioactive double-labeled culture, and with a 5'-nucleotidase-deficient, mutant strain. The adenosine formed is further phosphorolyzed to adenine as a prerequisite for its uptake and incorporation. The cellular localization of the enzymes involved in the catabolism of adenosine 5'-monophosphate is discussed.
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PMID:Uptake of adenosine 5'-monophosphate by Escherichia coli. 108 26

We investigated the effects of phorbol myristate acetate (PMA) on metabolic pulmonary endothelial ectoenzyme dysfunction. Anesthetized rabbits were placed on total heart bypass, and the single-pass transpulmonary metabolism of [3H]benzoyl-Phe-Ala-Pro (BPAP) by endothelial-bound angiotensin-converting enzyme (ACE) and [14C]adenosine 5'-monophosphate (AMP) by 5'-nucleotidase (NCT) was calculated before and after PMA (10 micrograms/kg iv), a dose that does not produce histologically evident endothelial damage. Under conditions of partial microvascular recruitment (blood flow = 400 ml/min through the entire lung), PMA, but not the vehicle, significantly reduced substrate utilization of both BPAP and adenosine 5'-monophosphate (AMP) and increased the apparent Michaelis constant (Km) values of ACE for BPAP, indicative of metabolic dysfunction. These changes were completely prevented by pretreatment with indomethacin. Under conditions of near full microvascular recruitment (blood flow = 640 ml/min through the left lung only), PMA similarly reduced substrate utilization and increased the apparent Km of ACE for BPAP. In this case, however, indomethacin failed to prevent the observed PMA-induced metabolic dysfunction. We conclude that PMA alters endothelial ectoenzyme substrate metabolism independently from changes in pulmonary blood flow; indomethacin appears to antagonize the effects of PMA under conditions of partial microvascular recruitment only, perhaps by diverting flow to previously unperfused, unexposed to PMA, and hence metabolically healthy vessels.
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PMID:Effects of indomethacin on PMA-induced pulmonary endothelial enzyme dysfunction in vivo. 131 16

Extracellular adenosine has the potential to influence many aspects of target cell metabolism. The present study has determined the endogenous levels of adenosine in the pregnant mouse uterus and developing embryo-decidual unit with respect to the expression of two key enzymes of adenosine metabolism, 5'-nucleotidase (5'-NT; EC 3.1.3.5) and adenosine deaminase (ADA; EC 3.5.4.4). To measure adenosine levels, nucleoside extracts were etheno-derivatized and quantitated by high-performance liquid chromatography-fluorescence detection (0.03 pmol/mg protein sensitivity). Adenosine levels were determined to be 0.18 nmol/mg protein in the nonpregnant uterus; however, two statistically significant changes were identified in the pregnant uterus: (1) a periimplantation surge between day 3 (0.24 nmol/mg protein) and day 5 (0.59 nmol/mg protein) of gestation (plug day 0; implantation day 4); and (2) an early postimplantation decline between day 6 (0.54 nmol/mg protein) and day 7 (0.10 nmol/mg protein). The periimplantation adenosine surge coincided with uterine expression of 5'-NT, an enzyme which catalyzes the irreversible dephosphorylation of 5'-AMP to adenosine. 5'-NT expression was shown by Northern blot analysis to peak in the embryo-decidual unit on day 5 of gestation and then to decline through day 9; transcripts remained elevated in the placenta between day 9 and day 13 (the latest day examined in this study). By use of specific enzyme histochemistry, most 5'-NT activity was localized to the primary decidual zone on day 5. This expression subsequently declined during regression of the primary decidua; however, 5'-NT appeared on giant trophoblast (days 7-13) and the metrial gland (days 11-13). Other purine catabolic enzymes degrading AMP (adenylate deaminase) or generating adenosine (S-adenosylhomocysteine hydrolase) were not detected in the embryo-decidual unit suggesting that the net flux of utero-placental AMP catabolism proceeds with adenosine as an intermediate, this being the major pathway of adenosine formation. The sharp drop in adenosine levels between day 6 and day 7 coincided with a rise in the activity and mRNA expression of ADA, an enzyme which catalyzes the irreversible deamination of adenosine to inosine. ADA was previously localized to the secondary decidual zone (days 6-11), secondary giant cells (days 7-13), and spongiotrophoblasts (days 8-13) in the mouse (Knudsen et al., 1991). Results of developmental Northern blot analysis demonstrated a direct correlation of relative 5'-NT/ADA mRNA band intensity to adenosine content between day 4 and day 9 of gestation, suggesting that the local availability of adenosine in the antimesometrium is dependent upon the distribution of these enzymatic activities.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Adenosine levels in the postimplantation mouse uterus: quantitation by HPLC-fluorometric detection and spatiotemporal regulation by 5'-nucleotidase and adenosine deaminase. 142 25


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