Showing papers on "Nucleotidase published in 1978"

Activities and some properties of 5'-nucleotidase, adenosine kinase and adenosine deaminase in tissues from vertebrates and invertebrates in relation to the control of the concentration and the physiological role of adenosine.

Abstract: 1 The maximal activities of 5′-nucleotidase, adenosine kinase and adenosine deaminase together with the Km values for their respective substrates were measured in muscle, nervous tissue and liver from a large range of animals to provide information on the mechanism of control of adenosine concentration in the tissues 2 Detailed evidence that the methods used were optimal for the extraction and assay of these enzymes has been deposited as Supplementary Publication SUP 50088 (16pages) at the British Library Lending Division, Boston Spa, Wetherby, West Yorkshire LS23 7BQ, UK,from whom copies can be obtained on the terms indicated in Biochem J (1978), 169, 5 This evidence includes the effects of pH and temperature on the activities of the enzymes 3 In many tissues, the activities of 5′-nucleotidase were considerably higher than the sum of the activities of adenosine kinase and deaminase, which suggests that the activity of the nucleotidase must be markedly inhibited in vivo so that adenosine does not accumulate In the tissues in which comparison is possible, the Km of the nucleotidase is higher than the AMP content of the tissue, and since some of the latter may be bound within the cell, the low concentration of substrate may, in part, be responsible for a low activity in vivo 4 In most tissues and animals investigated, the values of the Km of adenosine kinase for adenosine are between one and two orders of magnitude lower than those for the deaminase It is suggested that 5′-nucleotidase and adenosine kinase are simultaneously active so that a substrate cycle between AMP and adenosine is produced: the difference in Km values between kinase and deaminase indicates that, via the cycle, small changes in activity of kinase or nucleotidase produce large changes in adenosine concentration 5 The activities of adenosine kinase or deaminase from vertebrate muscles are inversely correlated with the activities of phosphorylase in these muscles Since the magnitude of the latter activities are indicative of the anaerobic nature of muscles, this negative correlation supports the hypothesis that an important role of adenosine is the regulation of blood flow in the aerobic muscles

Adenosine production in the ischemic kidney.

Abstract: We conducted experiments to determine (1) tissue, blood, and urine levels of adenosine produced by the ischemic kidney under conditions of renal artery occlusion, and (2) the site(s) of production and release of adenosine by the kidney. Concentrations of adenosine, inosine, and hypoxanthine in the dog urine were found to increase after 2 minutes of renal artery occlusion as were concentrations of these metabolites in renal tissue after 10 minutes of renal artery occlusion. Renal venous plasma levels of inosine and hypoxanthine also were elevated after 3 minutes of arterial occlusion. In modified stop-flow experiments, adenosine appeared in the urine in a peak that corresponded most closely with proximal tubule fluid. 5'-Nucleotidase, the enzyme which catalyzes the dephosphorylation of 5'-AMP or 5'-IMP to adenosine or inosine, respectively, was found to be located primarily on the external membranes and mitochondria of proximal tubule cells, but not in distal tubule or collecting duct cells. Since adenosine has been demonstrated to elicit renal vasoconstriction and is produced by the ischemic kidney, it is suggested that adenosine may be involved in the mediation of postocclusion renal ischemia.

Lymphocyte ecto-5'-nucleotidase deficiency in agammaglobulinemia.

Abstract: Fresh peripheral blood lymphocytes from eight patients with congenital agammaglobulinemia demonstrate reduced ecto-5'-nucleotidase activity when compared to the mean activity of normal subjects and patients with other forms of immunoglobulin deficiency. A specific defect of ecto-5'-nucleotidase is further suggested by normal values for lymphocyte ecto-adenosinetriphosphatase and ecto-nonspecific phosphatase. The data provide evidence for an enzyme deficiency in this X-linked, B lymphocyte deficiency syndrome.

Purine metabolism in lymphocytes from patients with primary hypogammaglobulinaemia.

Abstract: The previous report of low levels of purine 5'-nucleotidase activity in peripheral blood mononuclear cells (lymphocytes and monocytes) from patients with non-familial adult onset `variable' primary hypogammaglobulinaemia has been confirmed and the observation extended to include patients with other types of primary immunodeficiency. Patients with sex-linked congenital hypogammaglobulinaemia have values for mononuclear cell 5'-nucleotidase activity which are in the normal range, whereas most cases of non-familial adult onset `variable' primary hypogammaglobulinaemia have clearly subnormal values. The three patients with isolated IgA deficiency who were tested also had subnormal values. Evidence that the measured enzyme activity is in fact 5'-nucleotidase and independent of interfering phosphatase activities is presented. No significant or consistent alterations in the activities of the following enzymes were detected in mononuclear cells or erythrocytes: adenosine deaminase, purine nucleoside (inosine) phosphorylase, hypoxanthine phosphoribosyltransferase, adenine phosphoribosyltransferase, phosphoribosylpyrophosphate (PRPP) synthetase. The erythrocyte PRPP content and the mononuclear cell PRPP amidotransferase activity were normal in the small number of patients in which they were measured. These findings are discussed in the light of the current interest in the inter-relationship between some disorders of purine metabolism and the immunological deficiency syndromes.

Pyrimidine nucleoside monophosphate kinase from human leukemic blast cells.

Abstract: Pyrimidine nucleoside monophosphate kinase (EC 2.7.4.14) catalyzes the phosphorylation of various pyrimidine nucleoside monophosphates to their corresponding diphosphates. In addition to its role in the synthesis of nucleic acid precursors, this enzyme is essential for the conversion of the antileukemic agent 1-β-d-arabinofuranosylcytosine to its active metabolite 1-β-d-arabinofuranosyl 5′-triphosphate. Pyrimidine nucleoside monophosphate kinase has been purified 520-fold from human leukemic blast cells. Substrate specificity and kinetics for various pyrimidine nucleoside monophosphates and analogs have been investigated and compared with previous studies of this kinase isolated from other sources. A single enzyme appears responsible for the phosphorylation of cytidine 5′-monophosphate, deoxycytidine 5′-monophosphate, uridine 5′-monophosphate, and deoxyuridine 5′-monophosphate as well as the pharmacological substrates 1-β-d-arabinofuranosylcytosine 5′-monophosphate, 5-fluorouridine 5′-monophosphate, 5-fluorodeoxyuridine 5′-monophosphate, and 1-β-d-arabinofuranosyluracil 5′-monophosphate. Enzyme levels of pyrimidine nucleoside monophosphate kinase have been determined in leukocyte blast cells isolated from normal human donors (1.16 units/mg protein) and from patients with acute lymphocytic leukemia (1.96 units/mg protein), acute myelogenous leukemia (1.99 units/mg protein), and chronic myelogenous leukemia (1.88 units/mg protein). These levels are 100-fold higher than those of deoxycytidine kinase, the enzyme responsible for the initial phosphorylation of 1-β-d-arabinofuranosylcytosine. However, the affinity of deoxycytidine kinase for 1-β-d-arabinofuranosylcytosine (Km, 2.56 × 10−5m) is greater than that of the monophosphate kinase for 1-β-d-arabinofuranosylcytosine 5′-monophosphate (Km, 6.8 × 10−4m).

Analytical subcellular fractionation of needle-biopsy specimens from human liver

Abstract: 1. Fragments (2-20 mg wet wt.) of closed needle-biopsy specimens from human liver were disrupted in iso-osmotic sucrose and subjected to low-speed centrifugation. The supernatant was layered on a linear sucrose-density gradient in the Beaufay small-volume automatic zonal rotor. The following organelles, with equilibrium densities (g/ml) and principal marker enzyme shown in parentheses, were resolved: plasma membrane (1.12-1.14; 5'-nucleotidase); lysosomes (1.15-1.20; N-acetyl-beta-glucosaminidase); mitochondria (1.20; malate dehydrogenase); endoplasmic reticulum (1.17-1.21; neutral alpha-glucosidase); peroxisomes (1.22-1.24; catalase). 2. The distribution of particulate alkaline phosphatase and, to a lesser degree, leucine 2-naphthylamidase followed that of 5'-nucleotidase. gamma-Glutamyltransferase was associated with membranes of significantly higher equilibrium density than was 5'-nucleotidase. 3. The distribution of 12 acid hydrolases was determined in the density-gradient fractions. beta-Glucosidase had a predominantly cytosolic localization, but the other enzymes showed a broad distribution of activity throughout the gradient. Evidence was presented for two populations of lysosomes with equilibrium densities of 1.15 and 1.20 g/ml, but containing differing amounts of each enzyme. Further evidence of lysosomal heterogeneity was demonstrated by studying the distribution of isoenzymes of hexosaminidase and of acid phosphatase. 4. The resolving power of the centrifugation procedure can be further enhanced with membrane perturbants. Digitonin (0.12 mM) selectively disrupted lysosomes, markedly increased the equilibrium density of plasma-membrane components and lowered the density of the endoplasmic reticulum, but did not affect the mitochondria or peroxisomes. Pyrophosphate (15 mM) selectively lowered the equilibrium density of the endoplasmic reticulum.

Decrease in 5'-nucleotidase activity in malignant transformed and normal stimulated cells.

Abstract: Analysis of six different cell types of normal and transformed fibroblasts grown in vitro and of four different cell types of normal and leukemic lymphocytes grown in vivo have shown a marked decrease of 3- to 30-fold in the specific activity of 5'-nucleotidase in the malignant cells as compared to their normal parental cells. The results have also indicated that a serum stimulation of untransformed or normal fibroblasts and a stimulation of normal lymphocytes by concanavalin A resulted in a significant decrease in the specific activity of 5'-nucleotidase of the stimulated cultures as compared to the resting cells. In both the malignant cells and the stimulated normal cells, the decrease in 5'-nucleotidase activity was not accompanied by a similar decrease in the specific activity of acid phosphatase, indicating a specific enzyme alteration in the surface membranes of the transformed and the normal stimulated cells.

Alteration of some functional and metabolic characteristics of resident mouse peritoneal macrophages by lymphocyte mediators.

Abstract: Resident mouse peritoneal macrophages were incubated in Sephadex G-100 fractions of supernates from concanavalin A-stimulated lymphocytes. A significant effect of the lymphocyte supernatant fractions containing mediators on macrophage 5'-nucleotidase, glucose-1 14C oxidation, cell maintenance, and migration is reported. The 5'-nucleotidase was depressed to an extent similar to that seen in activated macrophages obtained from Listeria-infected mice. On the other hand, glucose-1-14C oxidation was enhanced, but not to the same degree as seen in the counterparts in vivo. Whereas migration inhibitory factor (MIF) and cell adherence-augmenting activity were found in a number of adjacent fractions, the metabolic effects were found predominantly in a single fraction. Resident peritoneal macrophages or those elicited by the injection of a lymphocyte-derived chemotactic factor were more responsive with respect to the biochemical changes than caseinate-elicited macrophages. On the other hand, caseinate-elicited macrophages appeared to be more sensitive with respect to the effects of mediator(s) on cell retention. A possible dissociation between MIF and cell-adherence augmenting activity, on the one hand, and the entities that stimulate glucose-1-14C oxidation is reported, based on fractionation studies, and loss of the latter activity upon storage of lymphocyte supernates.

Characterization of HeLa 5'-nucleotidase: a stable plasma membrane marker.

Abstract: 5'-Nucleotidase, assayed as 5'-AMPase, has been extensively characterized and established as a stable, quantitative plasma membrane marker in HeLa S3 cells. The membrane 5'-AMPase has a Km of 7.0 microM. Relative affinities of the other 5'-mononucleotides for the enzyme are 5'-GMP > 5'-TMP > 5'-UMP > 5'-CMP. There are activity optima at pH7 and 10; the latter is Mg(2+)-dependent. The membrane preparations have a small amount of acid phosphatase activity that is distinct from 5'-AMPase activity but no alkaline phosphatase. AOPCP, ADP, and ATP are strongly inhibitory. Mg2+, Ca2+, or Co2+ additions do not affect the pH 7.0 activity; Mn2+ activates slightly, whereas Zn2+, Cu2+, and Ni2+ are inhibitory. EDTA slowly inactivates, but removal of the EDTA without the addition of divalent cations restores activity. The inactivation is also substantially reversed by Co2+ or Mn2+, but reactivability by divalent cations decreases with time in EDTA. ConA strongly inhibits, and alpha-methyl-D-mannoside or glucose (the latter much less efficiently) relieves the inhibition, indicating that the 5'-AMPase is a glycoprotein. Histidine is also inhibitory. Ouabain, phloretin, cytochalasin B, cysteine, phenyl-alanine, MalNEt, and IAA are without effect. 5'-AMPase activity codistributes with pulse-bound [3H]ouabain when either of two cell fractionation procedures are used. The 5'-AMPase activity per cell is constant at different cell densities in exponentially growing cells, and activity per unit cell volume remains constant throughout the cell cycle. These properties, together with its absence in other organelles, its stability to storage, its insensitivity to certain experimental manipulations, and its general insensitivity to inhibitors of specific transport systems, make 5'-AMPase a useful quantitative marker in studies on the regulation of HeLa membrane transport systems. Key Words: HeLa, 5'-nucleotidase, plasma membrane marker, non-specific phosphatases, divalent ions, ConA, AOPCP, cell cycle, mitochondria, transport inhibitors.

Characterization of analog resistance and purine metabolism of adult rat-liver epithelial cell 8-azaguanine-resistant mutants

Abstract: Adult rat-liver epithelial cultures were sensitive to the lethal effects of 8-azaguanine (AG), but lines contained variants resistant to AG. The frequency of retrievable AG-resistant colonies varied with both the concentration of AG used and the seeding density of the population under selection. Cells resistant to AG were also cross-resistant to 6-thioguanine and unable to grow in medium containing hypoxanthine, aminopterin and thymidine. Resistance was stable. AG resistance was due to a deficiency of hypoxanthine-guanine phosphoribosyl transferase (HGPRTase) activity which was not caused by an inhibitor. In the assay for HGPRTase, a substantial amount of product appeared as inosine (In) in addition to inosine monophosphate (IMP). Purine nucleoside phosphorylase will generate In from hypoxanthine and, indeed, the cells did possess this activity. However, several findings indicated that the In was derived from IMP by catabolism by 5'-nucleotidase (NTase): (1) IMP decreased as In increased and (2) the inhibitors of NTase, adenosine monophosphate and thymidine triphosphate, reduced the generation of In by over 90% without inhibiting purine nucleoside phosphorylase. The cells possessed substantial NTase activity, 35% of which was located in the cytosol along with 69% of HGPRTase. Several lines of evidence suggested that the NTase activity limited the amount of 8-azaguanylic acid presented to the cells by catabolising the nucleotide and, thereby, reducing the toxicity of available AG.

Adenine nucleotides in cholinergic transmission: presynaptic aspects.

Abstract: 1. Isolated nerve terminals (T-sacs and synaptosomes) prepared from the purely cholinergic Torpedo electric organ have been studied for their ability to incorporate and metabolise [2-3H] adenosine and to degrade 5'-AMP to adenosine. 2. A temperature-dependent, saturable uptake system for adenosine was found with kinetic properties similar to nucleoside transport systems in other cells. The uptake system in Torpedo nerve terminals was inhibited by 2'-deoxyadenosine, a known inhibitor of adenosine transport. 3. Intraterminal adenosine is rapidly metabolised to a number of products including AMP, ADP and ATP. 4. Isolated nerve terminals contain considerable 5'-nucleotidase activity, most of which resides on the outer face of the external membrane. The Km of the enzyme is congruent to 5 micron and it is inhibited by a phosphonate analogue of ADP, alpha-beta-methylene-ADP. It is suggested that this 5'-nucleotidase plays an important role in the production of adenosine from a nucleotide pool in the synaptic cleft.

Pyrimidine metabolism in hereditary erythrocyte pyrimidine 5′ nucleotidase deficiency

Abstract: A patient with hereditary erythrocyte pyrimidine 5′ nucleotidase deficiency was studied to determine the mechanism of accumulation of erythrocyte pyrimidine nucleotides Estimates of the rate of degradation of uridine nucleotides to diffusable products imply that the high levels found in these patients could not be sustained from the degradative pathways alone Active synthesis of uridine nucleotides was found to occur in erythrocytes from both patient and control blood samples when either uridine or orotate was used as a substrate The circulating levels of uridine in the blood are such that sufficient nucleotides to account for the high levels seen in these patients could accumulate in the erythrocytes from biosynthetic pathways alone, quite apart from the contribution from degradation of residual ribosomal RNA This provides scope for new therapeutic approaches; treatment with allopurinol, however, was found to result in an increase, rather than a decrease, in erythrocyte pyrimidine nucleotides

Ecto 5'-nucleotidase deficiency in primary hypogammaglobulinaemia.

Abstract: The activity of the lymphocyte ectoenzyme 5'-nucleotidase is very low in the majority of patients with primary 'common variable' hypogammaglobulinaemia. In order to test whether this can be explained by lymphocyte subpopulation deficiencies we measured 5'-nucleotidase activity, using both biochemical and histochemical techniques, in purified T and B cells from patients and healthy subjects. Purified B cells from normal subjects have about four times the activity of T cells. This explains why the levels of lymphocyte 5'-nucleotidase activity are at the lower limit of the normal range in patients with X-linked hypogammaglobulinaemia who lack B cells. The low levels in the 'common variable' group can be explained by low activity in their T lymphocytes associated with either low activity in their B cells or depletion of B cells. The finding that inhibition of the enzyme does not interfere with in vitro lymphocyte transformation or immunoglobulin production in normal subjects indicates that the enzyme deficiency is not directly responsible for the hypogammaglobulinaemia. These and other studies suggest that this enzyme appears on lymphocytes at a certain stage of development and that both T and B lymphocytes in some patients with 'common variable' hypogammaglobulinaemia are developmentally immature.

Human erythrocyte proteins associated with adenosine 3',5'-cyclic monophosphate action.

Abstract: Two adenosine 3',5'-cyclic monophosphate (cyclic-AMP)-binding protein factors (molecular weight 230,000) have been partially purified from human erythrocytes. One of these proteins seems to be different from the cyclic-AMP-binding component of the cyclic-AMP-dependent protein kinases. These protein factors are also capable of binding adenosine. We present data also on two forms of cyclic-AMP-dependent protein kinases (ATP: protein phosphotransferase, EC 2.7.1.37) partially purified from the cytosol of normal human erythrocytes. Kinase I has been classified as type I enzyme on the basis of its activation when preincubated with protamine, histone or NaCl. The substrate specificities of the two kinases and many of their kinetic parameters are rather similar. Their subunit structure is reminiscent of that of kinases obtained from other sources. The catalytic subunit of both enzymes reversibly cross-react with the regulatory subunit of kinase I from the rabbit red blood cell.

[41] Pyrimidine nucleoside monophosphate kinase from rat liver and rat Novikoff ascites hepatoma (EC 2.7.4.14)

Abstract: Publisher Summary This chapter describes the pyrimidine nucleoside monophosphate kinase from rat liver and rat Novikoff ascites hepatoma. The enzyme occupies a strategic position in the biosynthesis of pyrimidine nucleotides because its phosphate-acceptor substrates are products of both the de novo and the salvage pathways. The phosphate-acceptor specificity is peculiar because the enzymes catalyzes the phosphorylation of cytidine monophosphate (CMP), deoxycytidine monophosphate (dCMP), and uridine monophosphate (UMP) but not deoxyuridine monophosphate (dUMP) that differs from UMP by only one atom of oxygen just as dCMP differs from CMP. Two methods of assay are used. The radiochemical assay measures the conversion of nucleoside monophosphate to nucleoside diphosphate or the transfer of γ-phosphate from adenosine tri phosphate (ATP) to the nucleoside monophosphate by separation of reactants and products on paper electrophoresis. In the latter assay, pyruvate kinase is coupled with lactate dehydrogenase to measure adenosine diphosphate (ADP) formation. When ATP or deoxyadenosine triphosphate (dATP) serve as phosphate donor, substrate inhibition occurs at concentrations of CMP greater than 0.13 mM.

Catabolism of adenosine 5'-monophosphate in promastigotes of Leishmania tropica.

Abstract: The specific activities of enzymes participating in AMP-catabolizing reactions in promastigotes of Leishmania tropica were determined. The following sequence of reactions is suggested: AMP leads to adenosine leads to adenine leads to hypoxanthine. The initial enzyme of this sequence, AMP nucleotidase, is apparently membrane-bound. The significance of AMP catabolism with respect to adenylate energy charge and a signal transfering mechanism is discussed. Adenine deaminase has been partially purified and characterized. Several purine analogues, inter alia allopurinol, proved to be inhibitors of the adenine deaminase catalyzed reaction.

Effect of phosphate esters, nucleotides and nucleosides on 5'-nucleotidase of cultured mouse macrophages.

Abstract: Mouse peritoneal macrophages elicited by intraperitoneal injection of sodium caseinate exhibit low levels of ecto-5'-nucleotidase (E. C. 3.1.3.5) activity in contrast to macrophages obtained by peritoneal lavage. When elicited cells were cultured under standard conditions in the presence of serum, a 2.5-fold increase in 5'-nucleotidase activity was observed over a period of 48 hours. Addition of adenosine monophosphate to the culture medium led to an augmented (5-fold) increase in the specific activity (per unit cell protein) as well as an absolute increase (per culture plate) of 5'-nucleotidase. Other adenosine-containing compounds also had stimulatory effects. The levels of this enzyme thus appear to be regulated by the extracellular levels of adenosine nucleotides. The product of the enzymatic reaction--adenosine--when added to the medium exhibited a toxic effect on these cells--as did adenosine monophosphate. However, the former substance did not augment the increase in enzyme activity during culture. The toxic effect could be suppressed when the cells were cultured in the presence of uridine 5'-monophosphate. The latter substance also depressed the stimulation of enzyme activity due to AMP.

Partial purification and properties of an acid nucleotidase from the postmicrosomal supernatant of rat spleen

Abstract: 1. The dephosphorylation of 3′-AMP, 3′-dAMP, 3′-CMP and 3′-dCMP was studied in the postmicrosomal supernatant of rat spleen and liver. In both organs 3′-AMP and 3′-dAMP were dephosphorylated at an appreciable rate, in both the presence and the absence of Mg 2+ . The pH optimum for this dephosphorylation was in the range 4.5–5.0. 3′-CMP and 3′-dCMP were very slowly degraded, though the activity towards 3′-dCMP increased somewhat in the presence of Mg 2+ . The optimum pH for this Mg 2+ -dependent dephosphorylation was 5.5–6.0. 2. The rate of dephosphorylation of 3′-AMP and 3′-dAMP per mg of protein was about 5 times as high in spleen as in liver. 3. The dephosphorylation of 3′-AMP could be ascribed to a single enzyme with pH optimum about 4.5. The activity towards 3′-dAMP could be resolved into one component coinciding with the 3′-dAMP-degrading enzyme, and one Mg 2+ -requiring component probably identical with the soluble deoxyinosine-activated nucleotidase. The dephosphorylation of 3′-dCMP seemed to be performed only by the latter enzyme. 4. The enzyme dephosphorylating 3′-AMP was purified 200-fold from the postmicrosomal supernatant and its physical and catalytic properties were compared with those of acid nucleotidase (EC 3.1.3.31) purified from rat liver lysosomes. The two enzymes were identical in all properties tested (substrate specificity, K m , molecular weight, response to phosphatase inhibitors), but some of the data differed from earlier reports on the acid nucleotidase. 5. The subcellular localization of the acid nucleotidase, its relationship to the acid phosphatase(s) and its role in the breakdown of nucleic acid constituents are discussed.

Origin of an elevated plasma alkaline phosphatase activity in non-jaundiced patients.

Abstract: Samples from 260 non-jaundiced patients with elevated plasma alkaline phosphatase activities were analysed for gamma-glutamyltransferase and 5'-nucleotidase activity, and for alkaline phosphatase isoenzyme pattern. The plasma gamma-glutamyltransferase activity was found to be a more sensitive index than that of plasma 5'-nucleotidase in confirming the presence of a liver component of the elevated plasma alkaline phosphatase. If the gamma-glutamyltransferase level is normal it is probable that the increase in plasma alkaline phosphatase activity is of bone origin. However, and elevated gamma-glutamyltransferase result does not exclude a bone component; in this situation plasma alkaline phosphatase isoenzymes should be estimated. The causes of elevated activities of plasma alkaline phosphatase, 5'-nucleotidase and gamma-glutamyltransferase, found in this investigation were generally the same as those found by other worker. The effect of treatment by drugs on gamma-glutamyltransferase, an inducible enzyme, needs more investigation.