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)

Cross-resistance patterns between chemotherapeutic agents have implications for the treatment of hematologic and other diseases. Previous in vitro models have shown cross-resistance between the purine analog 2-chlorodeoxyadenosine (cladribine) and the pyrimidine analogs 2',2'-difluorodeoxycytidine (gemcitabine) and 1-beta-D-arabinofuranosylcytosine (cytosine arabinoside, cytarabine) with reduced deoxycytidine kinase (dCK) activity as the underlying determinant of resistance. In this study, we continuously exposed the human promyelocytic leukemia cell line HL60 to as much as 1024 nM cladribine. After limiting dilution, the cladribine concentrations that caused 50% growth inhibition (IC50) of the two clones R13 and R23 were 33.3- and 18.7-fold, respectively, higher than the IC50 of the parental HL60 cells (8.7+/-1.3 nM). These cladribine-resistant clones, however, showed no cross-resistance to gemcitabine and only 3.3- and 2.7-fold resistance to cytarabine, respectively. Characterization of both clones revealed stably elevated levels of purine-specific "high-Michaelis constant (Km)" 5'-nucleotidase (5'-NT) messenger RNA expression and specific activity, whereas pyrimidine-specific "low-Km" 5'-NT activity was undetectable, and dCK activity was only marginally decreased in R13. Thus, the ratio of dCK (specific for cladribine) to high-Km 5'-NT activity in R13 and R23 was reduced to 65.3% and 63.7%, respectively. These results show that changes of high-Km 5'-NT activity can induce cladribine resistance, without cross-resistance to gemcitabine.
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PMID:Lack of cross-resistance with gemcitabine and cytarabine in cladribine-resistant HL60 cells with elevated 5'-nucleotidase activity. 984 78

The activities of two ectoenzymes,Mg(2+)-ATPase (ATPase) and 5'-nucleotidase (5'-NT) from tonsillar mononuclear cells (TMC) and peripheral blood mononuclear cells (PBMC) were investigated in idiopathic tonsillar hyperplasia and recurrent tonsillitis. The ATPase activity of TMC was significantly higher in recurrent tonsillitis than in idiopathic tonsillar hyperplasia, whereas no difference was demonstrated in ATPase activity of PBMC. The activity of 5'-NT was similar in both investigated groups. However, ATPase and 5'-NT activities were significantly higher in TMC compared to PBMC. Such results suggest a possible role of ATPase in the activation of TMC during the course of chronic tonsillitis and indicate a difference in the function of TMC and PBMC.
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PMID:Divalent cation-activated-ATPase and ecto 5'-nucleotidase activities in chronic tonsillitis. 989 64

The crystal structure of 5'-nucleotidase (5'-NT) from E. coli, also known as UDP-sugar hydrolase, has been determined at 1.7 A resolution. Two zinc ions are present in the active site, which is located in a cleft between two domains. The dimetal center and a catalytic Asp-His dyad are the main players in the catalytic mechanism. Structure-based sequence comparisons show that the structure also provides a model for animal 5'-NTs, which together with other ectonucleotidases terminate the action of nucleotides as extracellular signaling substances in the nervous system.
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PMID:X-ray structure of the Escherichia coli periplasmic 5'-nucleotidase containing a dimetal catalytic site. 1033 72

A series of structurally related flavonoids and related compounds were evaluated whether they have inhibitory properties on the 5'-nucleotidase (5'-ribonucleotide phosphohydrolase; EC 3.1.3.5, 5'-NT) activity. Some of the flavonoids tested inhibit the enzyme such as quercetin, morin, apigenin, chrysin, myricetin, luteolin, diosmetin, (+/-)naringenin and diosmin. Rutin, naringin, hyperosid, (+/-)catechin, caffeic acid and rosmarinic acid had no inhibitory effect on the 5'-NT activity. Myricetin and quercetin were the most potent inhibitors for 5'-NT with IC50 values of 1.1 and 1.4 microM, respectively. Kinetic analysis showed a mixed type of inhibitor for both myricetin (Ki = 1.5 microM at pH 7.45), and quercetin (Ki = 0.6 microM at pH 7.45). The K(m) value for 5'-adenosine monophosphate (5-AMP) was determined with 77 microM at pH 7.45. The differential inhibitory potencies of flavonoids seem to be structurally related (hydroxylation pattern). The results demonstrate that some flavonoids are strong inhibitors of 5'-NT activity which can be correlated to their pharmacological effects.
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PMID:In vitro effects of selected flavonoids on the 5'-nucleotidase activity. 1039 92

Extracellular cyclic AMP is source of extracellular adenosine in brain and kidney. Whether this occurs in adipose tissue is unknown. The present study evaluated the capacity of swine adipocyte plasma membranes to metabolize cyclic AMP to AMP and adenosine, via phosphodiesterase (PDE) and 5'-nucleotidase (5'-NT), respectively. Plasma membranes (PM) and microsomal membranes (MM) were isolated from over-the-shoulder subcutaneous adipose tissue of 3 month-old male miniature swine. The purity of the membrane fractions was determined and PDE and 5'-NT activities in PM and MM fractions were corrected for cross-contamination. The maximal activity of MM-PDE was 7-fold greater than that of PM-PDE. MM-PDE was 100% inhibited by 5 microM cilostamide, while PM-PDE was unaffected by this PDE3B inhibitor. Inhibitors of PDE1, PDE2, PDE4 and PDE5 also failed to inhibit PM-PDE. However, 1 mM DPSPX inhibited PM-PDE activity by 72%. When PM were incubated with 0.8 microM cyclic AMP for 20 min, AMP accumulation was four times that of adenosine. These data demonstrate that cyclic AMP can be converted to AMP and adenosine by the PM-bound enzymes 5'-NT and PDE, and suggest that the PM-PDE responsible for extracellular cyclic AMP metabolism to AMP is distinct from the intracellular MM-PDE.
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PMID:Cyclic AMP metabolism by swine adipocyte microsomal and plasma membranes. 1058 21

2F-Adenine arabinoside (fludarabine, Fara-A) and 2-chloro-2'-deoxyadenosine (cladribine, CdA) are nucleoside analogues with antineoplastic activity in vitro and in vivo. Lack of clinical resistance between CdA and Fara-A has been demonstrated in patients with chronic lymphocytic leukemia (G. Juliusson et al., N. Engl. J. Med., 327: 1056-1061, 1992). To clarify the differences in mechanism of resistance to CdA and Fara-A in vitro, we developed two stable, resistant cell lines, HL60/CdA and HL60/ Fara-A, by exposure to increasing concentrations of analogues over a period of 8 months. Resistant cells tolerated >8,000 and 5-fold higher concentrations of CdA and Fara-A, respectively. The specific activity of the nucleoside phosphorylating enzyme (using deoxycytidine as substrate) in cell extracts from HL60/CdA and HL60/Fara-A mutants was about 10 and 60%, respectively, compared with the parental cell line. Western blot analysis using a polyclonal antibody showed no detectable deoxycytidine kinase (dCK) protein in CdA-resistant cells, whereas in Fara-A-resistant cells, it was at the same level as in the parental cells. The mitochondrial enzyme deoxyguanosine kinase was not altered in resistant cell lines. The HL60/CdA cells showed cross-resistance to 2-chloro-2'-arabino-fluoro-2'-deoxyadenosine, Fara-A, arabinofuranosyl cytosine, difluorodeoxyguanosine, and difluorodeoxycytidine toxicity, most likely because of the decreased phosphorylation of these analogues by dCK. Using real-time quantitative PCR, the mRNA levels of dCK and cytosolic 5'-nucleotidase (5'-NT), a major nucleoside dephosphorylating enzyme, were measured. It was shown that the dCK mRNA levels in both CdA- and Fara-A resistant cells were decreased in parallel with the activity. The expression of 5'-NT mRNA was not significantly elevated in CdA- and Fara-A resistant cells, as compared with the parental cells. Ribonucleotide reductase maintains a balanced supply of deoxynucleotide triphosphate pools in the cell and may also be a major cellular target for CdA and Fara-A nucleotides. Except for the deoxycytidine triphosphate level, the intracellular deoxynucleotide triphosphate pools were significantly higher in Fara-A-resistant cells compared with the parental cell line. This might be a consequence of mutation or altered regulation of ribonucleotide reductase activity and may explain the 2-5-fold cross-resistance to several nucleoside analogues observed with HL60/Fara-A cells. It is likely that the resistance for CdA was mainly attributable to a dCK deficiency, and Fara-A-resistant cells might have another contributing factor to the resistance beyond the dCK deficiency.
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PMID:Molecular and biochemical mechanisms of fludarabine and cladribine resistance in a human promyelocytic cell line. 1060 41

The expression of human purinergic P2 receptors (P2X1-7 and P2Y1-11) as well as the ecto-enzymes apyrase (CD39) and 5'-nucleotidase (CD73) was investigated on the nucleic acid level during granulocytic and monocytic differentiation of HL60 cells and on peripheral human blood leukocytes. RT-PCR and dot-blot hybridization assays indicated that mRNA transcripts of all analyzed P2 receptors apart from the P2X3 receptor were expressed during myeloid development of HL60 cells, showing a distinct regulation during the course of differentiation. In blood leukocytes, transcripts of P2X5, P2X7 and all P2Y receptors, except for P2Y6, receptor were found. CD39 and CD73 showed a marked upregulation during myeloid maturation. Functional analysis of P2 receptor-mediated intracellular Ca(2+)-increase after stimulation with ATP revealed no change during granulocytic differentiation, but showed a strong attenuation in both potency and efficacy during monocytic development of HL60 cells.
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PMID:Expression of purinergic receptors (ionotropic P2X1-7 and metabotropic P2Y1-11) during myeloid differentiation of HL60 cells. 1100 84

In order to characterize human colorectal cancer, much attention has been paid to enzyme studies. However, little is known about the correlation between the levels of key enzymes of purine nucleotide pathway and some clinical and biological indicators of tumor invasiveness and aggressiveness. Adenosine deaminase (ADA) and 5'-nucleotidase (5'-NT) were measured in cancerous and cancer-free adjacent large bowel tissues from 38 patients with colorectal carcinoma. We have analyzed the relationship between the enzyme levels and some clinical and pathological parameters. The enzymes' activities were markedly higher in primary tumors than in corresponding normal mucosae. The ADA level in tumor tissue was significantly correlated with lymph node metastasis, histologic type, tumor location, and patient's age, whereas the 5'-NT level showed a significant correlation with tumor grade and tumor location. ADA activity in tumor tissues was significantly higher in patients whose clinical course remained stable than in those with recurrent diseases. The purine metabolism and salvage pathway activity of purine nucleotides are accelerated in the cancerous human colorectal tissue. Although our findings suggest that these enzymes' activities are most likely related to the same histomorphological architecture of the tumor, the authors believe that long-term follow-up studies are needed to evaluate the prognostic value of purine enzymes for colorectal cancer.
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PMID:Activities of adenosine deaminase and 5'-nucleotidase in cancerous and noncancerous human colorectal tissues. 1111 12

We previously demonstrated that extracellular adenine nucleotides induced cyclic AMP elevation through local adenosine production at the membrane surface and subsequent activation of adenosine A(2A) receptors in NG108-15 cells. Furthermore, the adenosine formation was found to be mediated by an ecto-enzyme distinct from the ecto-5'-nucleotidase (CD73). In this study, we investigated the properties of the ecto-AMP phosphohydrolase activity in NG108-15 cells. NG108-15 cells hydrolyzed AMP to adenosine with the K:(M:) value of 18.8+/-2.2 microM and V(max) of 5.3+/-1.6 nmol min(-1) 10(6) cells(-1). This activity was suppressed at pH 6.5, but markedly increased at pH 8.5. The AMP hydrolysis was blocked by levamisole, an alkaline phosphatase (ALP) inhibitor. NG108-15 cells released orthophosphate from 2'- and 3'-AMP as well as from ribose-5-phosphate and ss-glycerophosphate, indicating that NG108-15 cells express ecto-ALP. The cyclic AMP accumulation induced by several adenine nucleotides was inhibited by levamisole, p-nitrophenylphosphate and ss-glycerophosphate, with a parallel decrease in the extracellular adenosine formation. Reverse transcriptase polymerase chain reaction analysis revealed that NG108-15 cells express mRNA for the tissue-nonspecific isozyme of ALP. These results demonstrate that AMP phosphohydrolase activity in NG108-15 cells is due to ecto-ALP, and suggest that this enzyme plays an essential role for the P1 antagonist-sensitive ATP-induced cyclic AMP accumulation in NG108-15 cells.
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PMID:Ecto-alkaline phosphatase in NG108-15 cells : a key enzyme mediating P1 antagonist-sensitive ATP response. 1113 45

Structures of nine independent conformers of E. coli 5'-nucleotidase (5'-NT) have been analyzed using four different crystal forms. These data show that the two-domain protein undergoes an unusual 96 degrees hinge-bending domain rotation. Structures of the open and closed forms with substrates and inhibitors reveal that the substrate moves by approximately 25 A with the large domain rotation into the catalytic site. The domain motions derived from a comparison of the nine conformations agree well with motions obtained from a normal mode analysis in that all independent domain rotations are around axes that are roughly located in the plane which includes the domain centers and the hinge. Two residues, Lys355 and Gly356, form the core of the hinge region and undergo a large change of the main-chain torsion angles. The hinge-bending movement observed for 5'-nucleotidase differs markedly from a classical hinge-bending closure motion which involves an opening of the substrate or ligand-binding cleft between two domains. In contrast, the movement observed in 5'-nucleotidase resembles that of a ball-and-socket joint. The smaller C-terminal domain rotates approximately around its center such that the residues at the domain interface move in a sliding motion along the interface. Few direct interdomain contacts and a layer of water molecules between the two domains facilitate the sliding motion.
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PMID:E. coli 5'-nucleotidase undergoes a hinge-bending domain rotation resembling a ball-and-socket motion. 1149 Dec 94


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