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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)

A cytosolic 5'-nucleotidase, acting preferentially on IMP and GMP, has been isolated from human colon carcinoma extracts. This enzyme activity catalyzes also the transfer of the phosphate group of 5'-nucleoside monophosphates (mainly, 5'-IMP, 5'-GMP, and their deoxycounterparts) to nucleosides (preferentially inosine and deoxyinosine, but also nucleoside analogs, such as 8-azaguanosine and 2',3'-dideoxyinosine). It has been proposed that the enzyme mechanism involves the formation of a phosphorylated enzyme as an intermediate which can transfer the phosphate group either to water or to the nucleoside. The enzyme is activated by some effectors, such as ATP and 2,3-diphosphoglycerate. Results indicate that the effect of these activators is mainly to favor the transfer of the phosphate of the phosphorylated intermediate to the nucleoside (i.e., the nucleoside phosphotransferase activity). This finding is in accordance with previous suggestions that cytosolic 5'-nucleotidase cannot be considered a pure catabolic enzyme.
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PMID:Nucleoside phosphotransferase activity of human colon carcinoma cytosolic 5'-nucleotidase. 165 19

An impurity, probably an anion, present in some batches of the buffer substances 4-(2-hydroxyethyl) piperazine-1-ethanesulfonic acid (HEPES), 2-morpholinoethane sulfonic acid (Mes) and piperazine-1,4-bis(2-ethane sulfonic acid (Pipes), activates the soluble 5'-nucleotidase from rat kidney. The affinity of the enzyme for 5'-IMP and the Vmax were both increased by the unidentified activator. ATP and 2,3-diphosphoglycerate, known activators of the soluble 5'-nucleotidase, had no effect if the incubation media were buffered with batches containing high concentrations of the activating impurity. These results suggest that the impurity interacts with the soluble 5'-nucleotidase at the same site as ATP and 2,3-diphosphoglycerate, however with a much higher affinity than these two compounds. It is possible that the same impurity might interfere with other proteins for which ATP is a substrate or a ligand.
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PMID:Impurity in buffer substances mimics the effects of ATP on soluble 5'-nucleotidase. 166 52

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

The human erythrocyte generates high-energy adenosine triphosphate by anaerobic glycolysis and cycles oxidized and reduced nicotinamide adenine dinucleotide phosphate by the aerobic pentose phosphate shunt pathway. Certain enzymopathies of the pentose phosphate shunt are associated with hemolysis resulting from oxidative denaturation of hemoglobin. Glucose-6-phosphate dehydrogenase deficiency, an X-chromosome-linked disorder, is the prototype of these diseases and is genetically and clinically polymorphic. Six enzymopathies of anaerobic glycolysis cause hemolytic anemia; lactate dehydrogenase deficiency does not. In 2,3-diphosphoglycerate mutase deficiency, 2,3-diphosphoglycerate is greatly reduced and asymptomatic polycythemia is noted. Pyrimidine-5'-nucleotidase deficiency, an enzymopathy of nucleotide metabolism, is characterized by intracellular accumulations of pyrimidine-containing nucleotides, marked basophilic stippling on the stained blood film, splenomegaly, and hemolysis. Lead inhibits the nucleotidase and an identical syndrome occurs during severe lead poisoning. Hemolysis also accompanies an unusual enzymopathy characterized by a 40- to 70-fold increase (not decrease) in adenosine deaminase activity.
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PMID:Hemolytic anemias and erythrocyte enzymopathies. 299 Feb 76