Human Placental Cytoplasmic 5′-Nucleotidase: Kinetics and Molecular Properties

Madrid‐Marina, Vicente; Kaminska, J.; Fox, I. H.

doi:10.1007/978-1-4684-1248-2_46

Cited by 10 publications

(18 citation statements)

References 14 publications

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“…With all substrates, the protein showed saturation kinetics with highest affinity (and lowest activity) to dTMP, whereas highest activity was observed with dAMP (Table I). Similar to eukaryotic low K m 5Ј-nucleotidases (27,28), the K m values for all natural substrates were in the micromolar range (Table I). Like the Helicobacter pylori 5Ј-nucleotidase HppA (29), the E. coli YfbR hydrolyzed natural substrates with lower rate than that for pNPP.…”

Section: Screening Of Purified Proteins For Phosphatase Activity-supporting

confidence: 54%

Interaction of Genome-linked Protein (VPg) of Turnip Mosaic Virus with Wheat Germ Translation Initiation Factors eIFiso4E and eIFiso4F

Khan

Mizumoto

Ray

et al. 2006

Journal of Biological Chemistry

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To find proteins with nucleotidase activity in Escherichia coli, purified unknown proteins were screened for the presence of phosphatase activity using the general phosphatase substrate p-nitrophenyl phosphate. Proteins exhibiting catalytic activity were then assayed for nucleotidase activity against various nucleotides. ). Further biochemical characterization of SurE revealed that it has a broad substrate specificity and can dephosphorylate various ribo-and deoxyribonucleoside 5-monophosphates and ribonucleoside 3-monophosphates with highest affinity to 3-AMP. SurE also hydrolyzed polyphosphate (exopolyphosphatase activity) with the preference for short-chain-length substrates (P 20 -25 ). YfbR was strictly specific to deoxyribonucleoside 5-monophosphates, whereas YjjG showed narrow specificity to 5-dTMP, 5-dUMP, and 5-UMP. The three enzymes also exhibited different sensitivities to inhibition by various nucleoside di-and triphosphates: YfbR was equally sensitive to both di-and triphosphates, SurE was inhibited only by triphosphates, and YjjG was insensitive to these effectors. The differences in their sensitivities to nucleotides and their varied substrate specificities suggest that these enzymes play unique functions in the intracellular nucleotide metabolism in E. coli.DNA and RNA synthesis requires a continuous and balanced supply of the four deoxyribonucleotides and four ribonucleotides. A network of biosynthetic and catabolic enzymes regulates the size of each pool with the enzymes ribonucleotide reductase, nucleoside kinases, and nucleotidases playing the main roles (1). By opposing the phosphorylation of nucleosides by kinases, intracellular 5Ј-nucleotidases participate in substrate cycles that regulate the cellular levels of ribo-and deoxyribonucleoside monophosphates and thereby all ribo-and deoxyribonucleotide pools (1, 2).Nucleoside monophosphate phosphohydrolases or nucleotidases (EC 3.1.3.5 and EC 3.1.3.6) are phosphatases that specifically dephosphorylate nucleoside monophosphates to nucleosides and inorganic phosphate. Seven mammalian 5Ј-nucleotidases have been identified through cloning and biochemical characterization. These enzymes differ in tissue specificity, subcellular localization, primary structure, and substrate specificity (2). All act on nucleoside monophosphates producing free nucleosides and P i . Each natural nucleotide can be the substrate for several nucleotidases, because they have overlapping specificities. The ubiquitous ecto-5Ј-nucleotidase, eN, 1 is anchored to the surface of the plasma membrane, and AMP is considered to be its major physiological substrate (3). Five other nucleotidases, including dNT-1, occur in the cytosol and one (dNT-2) occurs in mitochondria. dNT-1 and dNT-2 show a preference for the dephosphorylation of dUMP and dTMP (4). The "high K m -nucleotidase" cN-II prefers GMP and IMP (5), the cytosolic nucleotidases cN-IA and cN-IB have a preference for dephosphorylation of AMP (6, 7), and PN-1 (or cN-III) is most active with CMP and UMP (8). For bovine cN-II...

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Section: Screening Of Purified Proteins For Phosphatase Activity-supporting

confidence: 54%

Interaction of Genome-linked Protein (VPg) of Turnip Mosaic Virus with Wheat Germ Translation Initiation Factors eIFiso4E and eIFiso4F

Khan

Mizumoto

Ray

et al. 2006

Journal of Biological Chemistry

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“…This is in accordance with the regulatory characteristics of human placental cytoplasmic 5'-nucleotidase (35). Under physiological conditions the enzyme appears to be regulated mainly by nucleoside 5'-monophosphates, nucleoside di-and triphosphates, and Mg2+, but not by inorganic phosphate.…”

Section: Resultssupporting

confidence: 86%

Adenine Nucleotide Catabolism in the Human Trophoblast Early and Late in Gestation

Vettenranta

Raivio

1988

Pediatr Res

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ABSTRACT. Trophoblastic cells were separated and cul-culture, perfusion, and serial samples of newly delivered, unpertured from human first trimester and term placentae for fused placental tissue. During hypoxia placental anaerobic glystudies on energy metabolism. Changes in the catabolism colysis is activated, as evidenced by increased uptake and conof prelabeled adenine nucleotides and the adenylate energy sumption of glucose and production of lactate (2,4,(7)(8)(9)(10)(11)(12). Stores charge (EC) were followed during energy deprivation. EC of glycogen, which are present in placental tissue throughout was 0.70 f 0.04 (mean f SD) in the first trimester and pregnancy, are well preserved, when exogenous glucose can be 0.65 + 0.08 in the term cells before experiments. Both used in accelerated glycolysis (2, 7). However, substantial glycoduring hypoxia (N2-atmosphere) and in the absence of genolysis takes place during hypoxia, when availability of free glucose, ATP and EC were preserved for up to 8 h. 2-glucose is limited (5,11,13). Despite the increase in ATP Deoxyglucose caused a fall in ATP to 12.1 + 5.0 and 14.8 production through anaerobic glycolysis, tissue ATP and total + 7.4% of initial levels, and in EC to 0.46 f 0.04 and 0.42 adenine nucleotides decrease under these circumstances. The EC + 0.05 in the first trimester and term cells, respectively. also declines from the normal range of 0.70-0.81 to 0.55-0.71In first trimester cells, inhibition of oxidative phosphoryl- (2,(7)(8)(9)(12)(13)(14). ation by rotenone in the absence of glucose resulted in aThe human placenta seems able to maintain major energysignificantly slower reduction of ATP and EC than after requiring processes (lipid and steroid synthesis, amino acid acdeoxyglucose, whereas in term cells, the initial responses cumulation, etc.) and a stable carbohydrate metabolism for were similar. Of total adenine nucleotides degraded, 7.1-several hours by anaerobic glycolysis alone (2, 4, 5, 11). When 10.5% were released extracellularly as adenosine, when its activity of glycolysis is decreased, these processes are rapidly deamination was inhibited. Human trophoblast appears to impaired (5, 7). tolerate transient hypoxia or deprivation of exogenousThe effects of energy substrate deprivation on the metabolically glucose. Susceptibility to energy deprivation increases with most active part of the placenta, the trophoblast, cannot be gestational age. The main pathway for AMP-catabolism is reliably judged on the basis of the studies referred to, because deamination, but the trophoblast is able to produce aden-the trophoblast constitutes only about 13-15 % of term placental osine during accelerated adenine nucleotide catabolism. weight (15). (Pediatr Res 24: 373-379,1988) It has also been shown that acute hypoxia enhances production of vasodilatatory prostaglandins in human placenta (16), and Abbreviations that adenosine is released from perfused tissue during ischemia (17). However, blood flow autoregulation reactive to hypoxia or EC, adenylate energy char...

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“…In addition to the well characterized membrane-bound 5Ј-nucleotidase (12), which is involved mainly in extracellular signaling, two cytosolic 5Ј-nucleotidases have been purified from human sources, and these are believed to be responsible for intracellular nucleotide catabolism. One of these cleaves various purine and pyrimidine monophosphates, with K m values in the low micromolar range (13). This ''low K m '' 5Јnucleotidase shows conventional hyperbolic kinetics and is competitively inhibited by ATP and ADP.…”

Section: Discussionmentioning

confidence: 99%

Developmental disorder associated with increased cellular nucleotidase activity

Page

Fontanesi

et al. 1997

Proc. Natl. Acad. Sci. U.S.A.

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Four unrelated patients are described with a syndrome that included developmental delay, seizures, ataxia, recurrent infections, severe language deficit, and an unusual behavioral phenotype characterized by hyperactivity, short attention span, and poor social interaction. These manifestations appeared within the first few years of life. Each patient displayed abnormalities on EEG. No unusual metabolites were found in plasma or urine, and metabolic testing was normal except for persistent hypouricosuria. Investigation of purine and pyrimidine metabolism in cultured fibroblasts derived from these patients showed normal incorporation of purine bases into nucleotides but decreased incorporation of uridine. De novo synthesis of purines and cellular phosphoribosyl pyrophosphate content also were moderately decreased. The distribution of incorporated purines and pyrimidines did not reveal a pattern suggestive of a deficient enzyme activity. Assay of individual enzymes in fibroblast lysates showed no deficiencies. However, the activity of cytosolic 5 -nucleotidase was elevated 6-to 10-fold. Based on the possibility that the observed increased catabolic activity and decreased pyrimidine salvage might be causing a deficiency of pyrimidine nucleotides, the patients were treated with oral pyrimidine nucleoside or nucleotide compounds. All patients showed remarkable improvement in speech and behavior as well as decreased seizure activity and frequency of infections. A double-blind placebo trial was undertaken to ascertain the efficacy of this supplementation regimen. Upon replacement of the supplements with placebo, all patients showed rapid regression to their pretreatment states. These observations suggest that increased nucleotide catabolism is related to the symptoms of these patients, and that the effects of this increased catabolism are reversed by administration of uridine.

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Human Placental Cytoplasmic 5′-Nucleotidase: Kinetics and Molecular Properties

Cited by 10 publications

References 14 publications

Interaction of Genome-linked Protein (VPg) of Turnip Mosaic Virus with Wheat Germ Translation Initiation Factors eIFiso4E and eIFiso4F

Interaction of Genome-linked Protein (VPg) of Turnip Mosaic Virus with Wheat Germ Translation Initiation Factors eIFiso4E and eIFiso4F

Adenine Nucleotide Catabolism in the Human Trophoblast Early and Late in Gestation

Developmental disorder associated with increased cellular nucleotidase activity

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