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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)

The growth of transformed mouse fibroblasts (3T6 cells) in medium containing 5% fetal bovine serum was inhibited after treatment with concentrations greater than 50 microM ATP, ADP, or AMP. Adenosine, the common catabolite of the nucleotides, had no effect on cell growth at concentrations below 1 mM. However, the following results indicate that the toxicity of ATP, ADP, and AMP is mediated by serum- and cell-associated hydrolysis of the nucleotides to adenosine. 1) ADP and AMP, but not ATP, were toxic to 3T6 cells grown in serum-free medium or medium in which phosphohydrolase activity of serum was inactivated. Under these conditions, the cells exhibited cell-associated ADPase and 5'-nucleotidase activity, but little ecto-ATPase activity. 2) Inhibition of adenosine transport in 3T6 cells by dipyridamole or S-(p-nitrobenzyl)-6-thioinosine prevented the toxicity of ATP in serum-containing medium and of ADP and AMP in serum-free medium. 3) A 16-24-h exposure to 125 microM AMP or ATP was needed to inhibit cell growth under conditions where serum- and cell-associated hydrolysis of the nucleotides generated adenosine in the medium continuously over the same time period. In contrast, 125 microM adenosine was completely degraded to inosine and hypoxanthine within 8-10 h. Furthermore, multiple doses of adenosine added to the cells at regular intervals over a 16-h period were significantly more toxic than an equivalent amount of adenosine added in one dose. Treatment of 3T6 cells with AMP elevated intracellular ATP and ADP levels and reduced intracellular UTP levels, effects which were inhibited by extracellular uridine. Uridine also prevented growth inhibition by ATP, ADP, and AMP. These and other results indicate that serum- and cell-associated hydrolysis of adenine nucleotides to adenosine suppresses growth by adenosine-dependent pyrimidine starvation.
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PMID:Growth inhibition of transformed mouse fibroblasts by adenine nucleotides occurs via generation of extracellular adenosine. 284 30

1. A 5'-nucleotidase with a strong preference for AMP over IMP was characterized in homogenates and subcellular fractions of pigeon heart by using concentrations of ATP, ADP and AMP which mimicked those present in the ischaemic tissue. 2. The AMP-5'-nucleotidase had a neutral pH optimum and an apparent Km in the range 4.6-5.2 mM. It was stimulated by ATP plus ADP, and was inhibited by other nucleoside monophosphates, Pi and p-nitrophenyl phosphate, but not by ribose 5-phosphate or beta-glycerophosphate. The enzyme was not inhibited by [alpha beta-methylene] ADP or by 5'-deoxy-5'-isobutylthioadenosine, an inhibitor of the previously purified IMP-preferring cytosolic 5'-nucleotidase. 3. Subcellular-fractionation studies indicated that the enzyme has access to cytosolic AMP, although it may be associated by weak ionic interactions with an organelle present in the low-speed particulate fraction. 4. A 5'-nucleotidase was detected under similar conditions in homogenates of rat heart. 5. The activity of the pigeon heart AMP-5'-nucleotidase was sufficient to account for previously measured rates of ischaemia-induced adenosine formation. The similar activity in rat heart could, however, account for only part of ischaemia-induced adenosine formation in this tissue.
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PMID:The pigeon heart 5'-nucleotidase responsible for ischaemia-induced adenosine formation. 284 63

An enzyme with FAD pyrophosphatase activity was extracted from human placental syncytiotrophoblast microvilli and purified to near-homogeneity. The enzyme has been identified as 5'-nucleotidase by several criteria. Throughout purification, parallel increases in the specific activities of FAD pyrophosphatase and AMP phosphatase were observed. The enzyme was a glycoprotein with a subunit molecular weight of 74,000. EDTA treatment resulted in a marked decline in both activities, and restoration of FAD pyrophosphatase activity but not 5'-nucleotidase activity was accomplished by the addition of Co2+ or, to a lesser extent, Mn2+. The substrate specificity of the 5'-nucleotidase activity that we observed agreed closely with the results of others. The pyrophosphatase activity was relatively specific for FAD. ADP, ATP, NAD(H), and FMN were not hydrolyzed, and ADP strongly inhibited both activities. For FAD pyrophosphatase activity, a Km of 1.2 x 10(-5) M and a Vmax of 1.1 mumol/min/mg protein were determined in assays performed in the presence of Co2+. In the absence of added Co2+, the Vmax declined but the Km was unchanged. For 5'-nucleotidase (AMP as substrate) the Km was 4.1 x 10(-5) M and the Vmax 109 mumol/min/mg protein. Hydrolysis of FMN to riboflavin was observed in partially purified detergent extracts of microvilli that contained alkaline phosphatase activity and lacked FAD pyrophosphatase and 5'-nucleotidase activity. The presence of both FAD pyrophosphatase and FMN phosphatase activities in syncytiotrophoblast microvilli supports the view that the placental uptake of vitamin B2 involves the hydrolysis of FAD and FMN to riboflavin which is then absorbed, a sequence postulated for intestinal absorption and liver uptake.
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PMID:5'-Nucleotidase of human placental trophoblastic microvilli possesses cobalt-stimulated FAD pyrophosphatase activity. 284 89

Adenosine formation and release was examined in 48 hr old primary cultures of chick ventricular myocytes. Dilazep greater than hexobendine greater than dipyridamole inhibit incorporation of adenosine into chick embryonic heart cellular nucleotides in a concentration dependent manner. A combination of 30 mM 2-deoxyglucose and 2 micrograms of oligomycin/ml reduces the ATP content of the cells by 71% in 10 min. This change is accompanied by an increase in total adenosine concentration of 3.4 nmoles/10(7) cells in 10 min. Although the ATP concentration is not altered during hypoxia (95%N2/5%CO2), adenosine concentration increases by 0.52 nmoles/10(7) cells in 30 min. When nucleoside incorporation is inhibited by 85-90% by dipyridamole, dilazep or hexobendine, efflux of adenosine decreases by 70-90%, and 60-90% of the newly formed adenosine is trapped inside the cells compared to 10% in the absence of the transport inhibitors. alpha, beta -Methylene ADP inhibits the ecto 5'-nucleotidase activity by 91 +/- 6% but does not inhibit adenosine formation or alter its distribution between cells and medium, thus ruling out the involvement of this enzyme in adenosine formation. We conclude that adenosine is formed intracellularly during 2-deoxyglucose and oligomycin-induced ATP degradation and during hypoxia and that the nucleoside is released via the symmetric nucleoside transporter.
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PMID:Intracellular adenosine formation and its carrier-mediated release in cultured embryonic chick heart cells. 284 8

5'-Nucleotidase (EC 3.1.3.5) activity was demonstrated in cryostat sections of rat liver using the Wachstein-Meisel medium and polyvinyl alcohol as tissue stabilizer. Optimum activity was obtained using an incubation medium containing 5 mM AMP, 10 mM magnesium chloride, 7.2 mM lead nitrate, 0.1 M Tris-maleate buffer, pH 7.2, and 17% (w/v) polyvinyl alcohol (Sigma, type III). The activity was localized at the bile canalicular and sinusoidal side of the plasma membranes of liver parenchymal cells as well as in the plasma membranes of endothelial cells of central veins and in fibroblasts surrounding portal tracts. The reaction was specific for 5'-nucleotidase because it was inhibited by ADP. Alkaline phosphatase did not interfere in the reaction. Cytophotometric analysis revealed a linear relationship between the formation of the final reaction product and incubation times up to 20 min and section thicknesses up to 8 micron. The activity in pericentral zones was 1.35 times the activity in periportal zones. The Michaelis constant for AMP was 1.4 mM in pericentral zones and 0.8 mM in periportal zones, suggesting that the bile canalicular and sinusoidal enzymes differ in their kinetic characteristics.
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PMID:A quantitative histochemical study of 5'-nucleotidase activity in rat liver using the lead salt method and polyvinyl alcohol. 285 Feb 87

Because adenosine plays a role in the regulation of glomerular filtration rate and of the release of renin, we examined the possibility of a local source for this mediator. We found that rat cultured glomerular mesangial cells converted 5'-AMP into adenosine. The properties of the enzyme involved in the reaction were those of an ecto-5' nucleotidase: (1) the products of the reaction were generated in the extracellular fluid although no 5'-nucleotidase was released by the cells into the medium; (2) identical activities were found for cultured cells in situ and sonicated cells; (3) the diazonium salt of sulfanilic acid which is a nonpenetrating reagent inhibited up to 75% of the enzyme activity. Ecto-5'-nucleotidase activity of intact cells obeyed Michaelis-Menten kinetics. Apparent Km for 5'-AMP was 0.32 mM. 5'-UMP was a strictly competitive inhibitor. ADP exerted a very powerful inhibitory effect and behaved also as a competitive inhibitor. ATP was inhibitory both by increasing Km and by decreasing Vmax. Ecto-5'-nucleotidase was active in the absence of divalent cations. However, Mg2+, Ca2+, Co2+ and Mn2+ were stimulatory. Zn2+ and Cu2+ suppressed the activity. Concanavalin A, a plant lectin, was markedly inhibitory, suggesting that a glycoprotein moiety was necessary to express enzyme activity. Ecto-5'-nucleotidase activity was not modified during phagocytosis of serum-treated zymosan by mesangial cells. Rat cultured glomerular epithelial cells exhibited a 5'-nucleotidase activity which was 4 times lower than that of the mesangial cells in primary culture.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Ecto-5'-nucleotidase of cultured rat mesangial cells. 285 4

Purified rat liver lysosomes contained 5'-nucleotidase activity which was 92 +/- 2% [4]latent. This latency was lost in response to a permeant sugar at a similar rate to that of the lysosomal marker enzyme beta-N-acetylglucosaminidase indicating that the 5'-nucleotidase was genuinely located in the lysosome and not a plasma membrane contaminant. Lysosomal 5'-nucleotidase exhibited the following properties characteristic of ecto-5'-nucleotidase inhibition by specific polyclonal antibodies: binding to a monoclonal antibody; inhibition by 1 mmol/1 alpha beta-methylene ADP; immunoreactive subunits of 70 and 38 kDa. Lysosomes in addition contained immunoreactive species of intermediate molecular mass.
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PMID:The presence and orientation of ecto-5'-nucleotidase in rat liver lysosomes. 298 12

Specific location of 5'-nucleotidase in the heart has been uncertain, some authors citing evidence for an exclusively non-myocyte location, while other data point to the existence of cytoplasmic and membrane-bound fractions. Single myocytes isolated from mature rat heart, and free of endothelial or interstitial cells, have been used to establish that muscle cells of the myocardium are rich in 5'-nucleotidase, exhibiting activity sufficient to account for the total myocardial content of this enzyme. All 5'-nucleotidase is accessible to extracellular AMP. Inhibitors of 5'-nucleotidase and adenosine transport have been used to establish that only the adenosine component of adenine nucleotides is taken up by myocytes, but hydrolysis of AMP by 5'-nucleotidase does not commit the adenosine formed to transport across the sarcolemmal membrane. Myocytes also have ecto-phosphatases which hydrolyse ADP and ATP.
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PMID:5'-Nucleotidase activity of isolated mature rat cardiac myocytes. 298 73

Zymosan particle-stimulated beta-galactosidase secretion by mouse peritoneal macrophages was found to be inhibited by micromolar concentrations of adenosine, AMP, ADP, and ATP. Inhibition by all four agents was increased to approximately 80% by adding erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA; 10 microM) an adenosine deaminase inhibitor, to the incubation medium. The inhibition of lysosomal enzyme secretion by ATP, ADP, and AMP was reversed by adding alpha, beta -methylene ADP (100 microM), a 5'-nucleotidase inhibitor, to the incubation medium. Inhibition by adenosine, however, was unaffected by alpha, beta -methylene ADP indicating that the inhibition by AMP, ADP, and ATP only occurred after they had been converted to adenosine by cell surface phosphohydrolases, including 5'-nucleotidase. Theophylline, a competitive antagonist of the binding of adenosine to plasma membrane adenosine receptors, failed to reverse the inhibitory effect of adenosine indicating the probable site of adenosine action to be intracellular. Other purine nucleosides, e.g., guanosine, and several purine and ribosemodified structural analogues of adenosine also inhibited zymosan-stimulated beta-galactosidase secretion, while xanthosine and certain pyrimidine nucleosides, e.g., thymidine, were inactive in this respect.
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PMID:Regulation of macrophage lysosomal secretion by adenosine, adenosine phosphate esters, and related structural analogues of adenosine. 298 3

ADP and ATP and their analogues were evaluated as inhibitors of 5'-nucleotidase purified from heart plasma membrane. ADP analogues are more powerful inhibitors than the corresponding ATP analogues. The most powerful inhibitor found is adenosine 5'-[alpha beta-methylene]diphosphate (AOPCP) for which the enzyme shows a Ki of 5 nM at pH 7.2. Measurements of pKi values for ADP and AOPCP as a function of pH indicate that the major inhibitory species of both nucleotides is the dianion. In the physiological range of pH values, AOPCP is a more powerful inhibitor than ADP principally because a higher percentage of AOPCP exists in the dianion form. The methylenephosphonate analogue of AMP (ACP), though not a substrate, is a moderately effective inhibitor. The corresponding analogues of ADP (ACPOP) and ATP (ACPOPOP) are as good inhibitors as ADP and ATP respectively. The thiophosphate analogues of ADP all inhibit 5'-nucleotidase, although not as powerfully as ADP, the most effective of these analogues being adenosine 5'-O-(1-thiodiphosphate) diastereoisomer B (ADP[alpha S](B)]. Other nucleotides inhibit the enzyme, but none is as effective as AOPCP. Inorganic tripolyphosphate and methylenediphosphonate are better inhibitors of the enzyme than is inorganic pyrophosphate. Inorganic thiophosphate is a better inhibitor than is orthophosphate. Hill plots of the ADP and AOPCP inhibition yield slopes close to 1; Hill plots of the ATP inhibition yield slopes of about 0.6. MgADP- is not an inhibitor, and MgATP2- is at best a very weak inhibitor of the enzyme.
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PMID:5'-Nucleotidase from rat heart membranes. Inhibition by adenine nucleotides and related compounds. 298 44


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