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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)

Human placental microsomal 5'-nucleotidase (EC 3.1.3.5) was prepared free of alkaline phosphatase by isoelectric focusing. A total of seven electrophoretic variants were isolated during the preparation of six placentas. Only three to six variants were found in a single placenta. The isoelectric pH's were 6.70, 6.44, 6.23, 6.02, 5.76, 5.63 and 5.44. These were found to be composed of variable quantities of a large, medium and low molecular weight form. The apparent molecular weights of the medium and light form of the enzyme were 86 500 and 43 500, respectively, as estimated from Stokes radius and sedimentation velocity determinations. The electrophoretic variants were not distinguishable with respect to specific activity and Michaelis constants for AMP, GMP or CMP or inhibition by ATP, CTP or adenosine. These electrophoretic variants appeared to be pseudoisozymes based upon different states of aggregation of a common primary sequence. There was a wide range of substrate specificity among nucleoside 5'-monophosphates which included 2-deoxyribose compounds. With AMP as 100, substrate activity was: CMP, 122; NMN, 74; GMP, 68: IMP, 63; XMP, 28 and UDP-glucose, 68. The Michaelis constants for AMP, GMP and CMP ranged from 12-18 muM, from 33-67 muM and from 170-250 muM, respectively. Although 5'-nucleotidase was active in the absence of divalent cation, 5 mM MgCl2 stimulated the enzyme activity to 234% of control and shifted the pH optimum of 9.8 to a plateau from pH 7.4-9.8.
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PMID:Purine catabolism in man: characterization of placental microsomal 5'-nucleotidase. 0 35

1. The kinetic properties of the 5'-nucleotidase (EC 3.1.3.5) present in the cytosol of rat liver were investigated in relation to the conversion of adenine nucleotides into uric acid, with particular reference to the stimulation of this process by fructose. The enzyme was assayed by the release of Pi and by a new and more sensitive radiochemical procedure. 2. When IMP was used as substrate, the partially purified enzyme displayed almost hyperbolic kinetics (h = 1.1) with S0.5 = 1.2 mM. Similar kinetics were observed with GMP and other nucleoside 5'-monophosphates, except AMP. 3. Vmax. of the enzyme for AMP was about the same as for IMP, but the kinetics were sigmoidal (h = 1.6) with S 0.5 = 10 mM. 4. The hydrolysis of IMP was inhibited competitively by GMP. IMP, at concentrations up to 0.5 mM, had a paradoxical stimulatory action on the hydrolysis of 2-5 mM-AMP and was inhibitory at higher concentrations. 5. The activity of the enzyme towards AMP and IMP was stimulated by ATP and GTP, and inhibited by Pi. Activators and inhibitor approximately cancelled each others' effects. At pH 7.4, the enzymic activity with 0.2 mM-AMP was undetectable under physiological conditions. 6. It is concluded that, in the liver cell, AMP is not hydrolysed by the soluble 5'-nucleotidase, but that its degradation requires prior deamination to IMP.
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PMID:A kinetic study of the soluble 5'-nucleotidase of rat liver. 1 87

Purine metabolism and reutilization pathways were studied as they applied to normal and leukemic leukocytes. The enzyme activities were expressed in terms of the quantity of protein extracted and per 10(10) cells. Whereas the protein extracted and the enzyme activities from normal lymphocytes were relatively constant, considerable variation was noted in cases of chronic lymphocytic leukemia (CLL). This variability in the properties of the leukemic cells suggests that the difference may be useful in the subclassification of the leukemias. The studies of the complete enzyme system were done with 300 million cells. The extraction of 350,000 normal lymphocytes/mul gave a soluble protein concentration of 1.46+/-0.16 mg protein per ml, and the yield from the same number of CLL lymphocytes varied between 0.72 and 8.32 mg protein per ml. The 5'-nucleotidase activity gave an inverse correlation with the amount of extractable protein. In individual cases of CLL, the protein concentrations and the 5'-nucleotidase activities were found on either side of the normal values. In most cases, the adenosine deaminase of CLL lymphocytic cell extracts was lower than normal, and the adenosine kinase was higher; in the CLL cells, these two enzymes gave a positive correlation with one another. Little or no difference was observed in the activities of the purine nucleoside phosphorylases in extracts of normal or leukemic lymphocytes and granulocytes. The hypoxanthine-guanine and adenine phosphoribosyltransferase activities increased in the leukemic granulocytes but almost always showed a decrease in the CLL lymphocytes when compared with the normal cells. Most of the leukemic cells had greater than normal activities of the enzymes synthesizing phosphoribosyl pyrophosphate when tested with the purines. The total nucleotide produced from adenine and guanine with adenine- and hypoxanthine-guanine phosphoribosyltransferase was about equal in normal and leukemic lymphocytes, but the proportion of the adenosine 5'-triphosphate in the product was much greater with the leukemic cells. This suggested that the ribosyltransferase activities were the same in both types of cells, but the nucleoside kinases and the nucleoside diphosphate kinases were more active in the leukemic cells. Inosine monophosphate dehydrogenase was less active than normal in the CLL cell extracts and was not directly related to the amount of inosine monophosphate generated from hypoxanthine.
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PMID:Purine metabolic cycle in normal and leukemic leukocytes. 18 45

In cultured cells established from Drosophila melanogaster embryos, and grown in usual medium, no hypoxanthine-guanine-phosphoribosyl transferase (HG-PRT) could be measured, and only traces of 5'-nucleotidase activity were detectable. On the contrary, it was observed that if the same medium is supplemented with purine bases, nucleosides, orotate, glutamine, azaserine or antifolates, de novo purine biosynthesis is inhibited, and HGPRT is detectable, along with an important 5'-nucleotidase activity. Moreover, dialysis or treatment of extracts from cells untreated by purines, with activated charcoal restored HGPRT and 5'-nucleotidase activities. These activities were abolished completely by inosinic acid (IMP) and guanosine 5'-monophosphoric acid (GMP). Similar results were obtained with fly extracts. These results suggest that de novo purine biosynthesis masks HGPRT activity, the endogenous synthesis leading to the accumulation of purine nucleotides which are inhibitors of the HGPRT activity.
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PMID:Regulation of purine biosynthesis in cultured Drosophila melanogaster cells: I.--Conditional activity of hypoxanthine-guanine-phosphoribosyltransferase and 5-nucleotidase. 21 63

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

Changes in hepatic purine enzyme activities of chicks fed diets containing 11%, 20%, 43% and 80% protein were correlated with protein intake and uric acid production in order to identify those enzymes with activities that parallel closely and may regulate uric acid production. Nucleoside phosphorylase, xanthine dehydrogenase, adenylosuccinate synthetase and adenosine kinase correlated positively with protein intake and uric acid production. Adenosine deaminase, 5'-nucleotidase (AMP), adenylate deaminase and adenine phosphoribosyltransferase correlated negatively with protein intake and uric acid production. Hypoxanthine phosphoribosyltransferase and 5'-nucleotidase (IMP) were unaffected by protein intake and did not correlate with uric acid production. The ratio of adenosine kinase to adenosine deaminase correlated positively with protein intake and uric acid production. The increased activities of adenylosuccinate synthetase and adenosine kinase, along with the reduced activities of 5'-nucleotidase and adenylate deaminase, in liver from chickens fed the 80% compared with the 11% protein diet demonstrate enhanced synthesis of adenine nucleotides. Since adenine nucleotides are essential cofactors for de novo purine synthesis, it is proposed that adenylosuccinate synthetase, adenosine kinase, 5'-nucleotidase and adenylate deaminase are key enzymes involved in the regulation of purine biosynthesis.
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PMID:Protein intake, hepatic purine enzyme levels and uric acid production in growing chicks. 61 42

Using 1-4C-labeled AMP and IMP as substrates, 5'-nucleotidase (5'-ribonucleotide phosphohydrolase, EC 3.1.3.5) activity was detected at the external surface of frog skeletal muscle with the active site facing toward the extracellular space. The enzyme was firmly bound to the muscle membrane. Its activity was dependent on Ca2+ or Mg2+ and was inhibited by non-radioactive ribonucleoside 5'-monophosphates, or theophylline, while adenosine 3'-monophosphate and p-nitrophenylphosphate had little or no effect. 5'-Nucleotidase with similar properties was also found in the isolated plasma membrane fraction of the muscle.
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PMID:5'-nucleotidase: an ecto-enzyme of frog skeletal muscle. 114 56

5'-nucleotidase (EC 3.1.3.5), an important enzyme in the metabolism of nucleotides, is generally accepted as a plasma membrane marker. The enzyme selectively splits phosphoric acid from 5' mononucleotides. Several methods are available for the histochemical localization of enzymes (antigenic properties of the enzyme protein, enzyme properties and activity and labelled specific inhibitors). Only the method based on enzyme properties has been used up to now in the case of 5'-nucleotidase. Free phosphoric acid liberated during the dephosphorylation of substrates such as AMP or IMP is rendered visible at the sites of 5' nucleotidase activity in the tissue by precipitation as lead or calcium phosphate. An improvement in the light microscopic technique is achieved by the use of freezedried tissue embedded in glycol methacrylate, whereby the histochemical reaction can be performed on semi-thin sections. Since lead phosphate is electron dense, these precipitates can easily be detected in the electron microscope too. Wide species and organ differences are found with respect to the distribution of 5'-nucleotidase activity. The well-known localization of the enzyme on the outer cell surface according to biochemical studies is confirmed by electron microscopic findings. A purely catabolic function of 5'-nucleotidase, as propounded in the literature, seems dubious since high 5'-nucleotidase activity was demonstrated in rapidly proliferating tissue too.
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PMID:[Light and electron microscopic localization of enzymes: 5'-nucleotidase (author's transl)]. 122 68

1. Activity of a cytoplasmic 5'-nucleotidase which preferentially hydrolyzes IMP and GMP (IMP-GMP 5'-nucleotidase) was determined by a specific immunochemical method in two species of birds and two species of mammals. 2. The activity was markedly high in avian liver, and it increased two-fold in response to a high protein diet in chicken liver. 3. In mammals, the activity was high in testis and spleen. In the rat, the activities in liver, kidney and heart extracts increased by about 30% in response to the high protein diet, while they increased three-fold in regenerating liver. 4. Low activities were detected in skeletal muscles and in erythrocytes of all the species studied.
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PMID:A comparative study on tissue distribution and metabolic adaptation of IMP-GMP 5'-nucleotidase. 133 84

Cytosolic 5'-nucleotidase has been implicated in the phosphorylation of certain nucleosides of therapeutic interest. In vitro, IMP and GMP serve as the optimal phosphate donors for this nucleoside phosphotransferase reaction. Existing assays for nucleoside phosphorylation effected by 5'-nucleotidase require a radiolabeled nucleoside as the phosphate acceptor and separation of the substrate-nucleoside from product-nucleotide has been accomplished either by a filter binding method or HPLC. However, detection of the phosphorylation of unlabeled nucleoside by HPLC is difficult since the ultraviolet absorbance of the phosphate donor, IMP, frequently obscures the absorbance of newly formed nucleotide. The use of ribavirin 5'-phosphate (RMP, 1,2,4-triazole-3-carboxamide riboside 5-monophosphate) as the phosphate donor obviates this difficulty since this triazole heterocycle does not significantly absorb at the wavelengths used to detect most nucleoside analogs. Using this procedure, a 5'-nucleotidase activity from the 100,000 x g supernatant fraction of human T-lymphoblasts deficient in adenosine kinase, hypoxanthine-guanine phosphoribosyltransferase, and deoxycytidine kinase, was characterized with regard to structure-activity relationships for certain inosine and guanosine analogs.
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PMID:A novel non-radioactive method for detection of nucleoside analog phosphorylation by 5'-nucleotidase. 143 Jul 86


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