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)

Deoxyadenosine metabolism was investigated in cultured human cells to elucidate the biochemical basis for the sensitivity of T lymphoblasts and the resistance of B lymphoblasts to deoxyadenosine toxicity. T lymphoblasts have a 20-to 45-fold greater capacity to synthesize deoxyadenosine nucleotides than B lymphoblasts at deoxyadenosine concentrations of 50--300 micron. During the synthesis of dATP, T lymphoblasts accumulate large quantities of dADP, whereas B lymphoblasts do not accumulate dADP. Enzymes affecting deoxyadenosine nucleotide synthesis were assayed in these cells. No substantial differences were evident in activities of deoxyadenosine kinase (ATP: deoxyadenosine 5'-phosphotransferase, EC 2.7.1.76) or deoxyadenylate kinase [ATP:(d)AMP phosphotransferase, EC 2.7.4.11]. The activity of 5'-nucleotidase (5'-ribonucleotide phosphohydrolase, EC 3.1.3.5) was increased 44-fold for AMP and 7-fold for dAMP in B lymphoblasts. A model for the regulation of deoxyadenosine nucleotide synthesis by 5'-nucleotidase activity is proposed on the basis of the observations.
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PMID:Biochemical basis for differential deoxyadenosine toxicity to T and B lymphoblasts: role for 5'-nucleotidase. 22 24

A purine 5'-nucleotidase has been separated by DEAE-Trisacryl chromatography from other 5'-nucleotidase activities present in human haemolysates and purified approx. 30,000-fold by subsequent chromatography on Blue Sepharose. The enzyme has an Mr of around 250,000, displays hyperbolic substrate-saturation kinetics and hydrolyses preferentially IMP, GMP and their deoxy counterparts. It is much less active with AMP and dAMP. The purine 5'-nucleotidase is inhibited by Pi, and is strongly stimulated by ATP, dATP and GTP, and by glycerate 2,3-bisphosphate. Stimulators decrease Km and increase Vmax. Glycerate 2,3-bisphosphate is the most potent stimulator of the enzyme and, under physiological conditions, over-rides the influence of the other effectors. Glycerate 2,3-bisphosphate also influences the binding of the enzyme to DEAE-Trisacryl, as evidenced by the different elution profile obtained with fresh as compared with outdated blood. It is concluded that the glycerate 2,3-bisphosphate-stimulated purine 5'-nucleotidase is responsible for the dephosphorylation of IMP and GMP, but not of AMP, in human erythrocytes.
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PMID:5'-Nucleotidase activities in human erythrocytes. Identification of a purine 5'-nucleotidase stimulated by ATP and glycerate 2,3-bisphosphate. 283 44

A human placental soluble "high Km" 5'-nucleotidase has been separated from "low Km" 5'-nucleotidase and nonspecific phosphatase by AMP-Sepharose affinity chromatography. The enzyme was purified 8000-fold to a specific activity of 25.6 mumol/min/mg. The subunit molecular mass is 53 kDa, and the native molecular mass is 210 kDa, suggesting a tetrameric structure. Soluble high Km 5'-nucleotidase is most active with IMP and GMP and their deoxy derivatives. IMP is hydrolyzed 15 times faster than AMP. The enzyme has a virtually absolute requirement for magnesium ions and is regulated by them. Purine nucleoside 5'-triphosphates strongly activate the enzyme with the potency order dATP greater than ATP greater than GTP. 2,3-Diphosphoglycerate activates the enzyme as potently as ATP. Three millimolar ATP decreased the Km for IMP from 0.33 to 0.09 mM and increased the Vmax 12-fold. ATP activation was modified by the IMP concentration. At 20 microM IMP the ATP-dependent activation curve was sigmoidal, while at 2 mM IMP it was hyperbolic. The A0.5 values for ATP were 2.26 and 0.70 mM, and the relative maximal velocities were 32.9 and 126.0 nmol/min, respectively. Inorganic phosphate shifts the hyperbolic substrate velocity relationship for IMP to a sigmoidal one. With physiological concentrations of cofactors (3 mM ATP, 1-4 mM Pi, 150 mM KCl) at pH 7.4, the enzyme is 25-35 times more active toward 100 microM IMP than 100 microM AMP. These data show that: (a) soluble human placental high Km 5'-nucleotidase coexists in human placenta with the low Km enzyme; (b) under physiological conditions the enzyme favors the hydrolysis of IMP and is critically regulated by IMP, ATP, and Pi levels; and (c) kinetic properties of ATP and IMP are each modified by the other compound suggesting complex interaction of the associated binding sites.
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PMID:High Km soluble 5'-nucleotidase from human placenta. Properties and allosteric regulation by IMP and ATP. 284 5

A DNA ligase has been purified from a subnuclear soluble replication complex isolated from adenovirus type 2-infected human KB cells. DNA ligase activity could not be demonstrated using an exogenous template until the complex was dissociated, suggesting that the ligase activity may be a component of the complex. The purified enzyme was free of endonuclease, exonuclease, 5'-nucleotidase, and phosphatase activities, and had a molecular weight of 105 000, as estimated by sedimentation in a glycerol gradient. The ligase requires ATP and a divalent cation for activity. The optimum of the reaction is at pH 7.8 in 50--100 mM Tris-HCl buffer and 10--20 mM MgCl2. Monovalent salts greatly stimulate ligase activity and the optimum was found at 150 mM. The reaction is very sensitive to high temperature; maximum activity was observed at 25--30 degrees C. ATP is the sole required cofactor and NAD, dATP and GTP could not replace the requirement for ATP. The Km for ATP is 60 microM. The Km for DNA is 250 microgram/ml or 1.6 nmol of terminal phosphate/ml and thus the enzyme shows relatively weak affinity for exogenous DNA. The maximum conversion of 32P into a phosphatase-resistant form is approximately 1.3% of the total, whereas T4 ligase, under the same conditions, can convert more than 25% of phosphate into a resistant form.
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PMID:Purification and properties of a DNA ligase from a soluble DNA replication complex. 735 2

The antiviral activity of azidothymidine (AZT), dideoxycytidine (ddC), and dideoxyinosine (ddI) against HIV-1 was comparatively evaluated in PHA-stimulated PBM. The mean drug concentration which yielded 50% p24 Gag negative cultures were substantially different: 0.06, 0.2, and 6 microM for AZT, ddC, and ddI, respectively. We found that AZT was preferentially phosphorylated to its triphosphate (TP) form in PHA-PBM rather than unstimulated, resting PBM (R-PBM), producing 10- to 17-fold higher ratios of AZTTP/dTTP in PHA-PBM than in R-PBM. The phosphorylation of ddC and ddI to their TP forms was, however, much less efficient in PHA-PBM, resulting in approximately 5-fold and approximately 15-fold lower ratios of ddCTP/dCTP and ddATP/dATP, respectively, in PHA-PBM than in R-PBM. The comparative order of PHA-induced increase in cellular enzyme activities examined was: thymidine kinase > uridine kinase > deoxycytidine kinase > adenosine kinase > 5'-nucleotidase. We conclude that AZT, ddC, and ddI exert disproportionate antiviral effects depending on the activation state of the target cells, i.e., ddI and ddC exert antiviral activity more favorably in resting cells than in activated cells, while AZT preferentially protects activated cells against HIV infection. Considering that HIV-1 proviral DNA synthesis in resting lymphocytes is reportedly initiated at levels comparable with those of activated lymphocytes, the current data should have practical relevance in the design of anti-HIV chemotherapy, particularly combination chemotherapy.
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PMID:Differential phosphorylation of azidothymidine, dideoxycytidine, and dideoxyinosine in resting and activated peripheral blood mononuclear cells. 838 46