Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: 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)

The adenine nucleotide pool of rabbit retina was labeled by an intravitreal injection in vivo of [3H]adenosine. Practically all the radioactivity was retained in the form of adenine nucleotides. The relative proportion of [3H]adenine nucleotides was the same as that of endogenous nucleotides. Potassium depolarization (43.6 mM) in vitro caused a rapid increase in the rate of release of radioactive purines. The radioactive material was composed of hypoxanthine, xanthine, inosine and trace amounts of adenine, adenosine and adenine nucleotides. The release of radioactive purines was delayed and reduced by the addition of the nucleoside inhibitor dipyridamole suggesting that the purines may be released in the form of nucleosides. Similarly, the addition of the ecto 5'-nucleotidase inhibitor alpha, beta-methylene ADP (AOPCP) did not alter the release of radioactivity or the composition of the released purines. Endogenous hypoxanthine, xanthine and inosine could be detected in the effluents, but there was only a very modest increase following potassium depolarization. There was a slight, but significant, decrease in the release of endogenous adenosine and increase in AMP after AOPCP. It is concluded that there is an intensive uptake and phosphorylation of adenosine in the rabbit retina. Depolarization induces release of radioactive purine nucleosides and bases. Most of these compounds appear to be released as such, but in addition there may be a small (maximally a few per cent of the total) fraction of the purines that are released as nucleotides.
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PMID:Release of endogenous and radioactive purines from the rabbit retina. 380 82

We measured adenosine release into venous plasma as an index of interstitial adenosine concentration during free flow exercise hyperemia. Isolated, blood-perfused dog calf muscles were stimulated at 6 Hz for 10 min at free flow. Plasma samples were collected before, during, and after the exercise period for analysis of plasma adenosine concentration [( ADO]) by HPLC. Adenosine release (Rado) was calculated as plasma flow times venous-arterial [ADO] difference. Rado (nmole/min/100 g) went from -0.1 +/- 0.1 at rest to 6.6 +/- 4.6 during 6-Hz exercise. Isoproterenol infusion, which caused an increase in blood flow equivalent to 6-Hz exercise, did not result in increased Rado. Infusion of the 5'-nucleotidase inhibitor, alpha, beta, methylene adenosine 5'-diphosphate (AOPCP) did not prevent the increase in Rado during exercise. These results support the hypothesis that interstitial adenosine concentration increases during sustained free flow twitch exercise and that this results in increased release of adenosine into venous plasma.
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PMID:Adenosine release into venous plasma during free flow exercise. 381 46

Angiotensin-converting enzyme and 5'-nucleotidase line the luminal surface of pulmonary microvascular endothelium and participate in the synthesis and/or degradation of potent vasoactive substances. We applied Michaelis-Menten kinetics in simultaneous estimations of apparent constants Km and Amax (product of Vmax and microvascular plasma volume) of these two enzymes for the substrates 3H-labeled benzoyl-Phe-Ala-Pro and 14C-labeled 5'-AMP, respectively, in vivo. Values of angiotensin-converting enzyme for benzoyl-Phe-Ala-Pro (Km = 10-11 microM; Amax = 12-13 mumol X min-1) were somewhat higher than published estimates in vitro and changed predictably in response to the known enzyme inhibitor captopril. Kinetic values of 5'-nucleotidase for 5'-AMP (Km = 3-4 microM; Amax = 3-4 mumol/min) were substantially lower than those reported in vitro but also responded predictably to the competitive inhibitor of 5'-nucleotidase, adenosine 5'-[alpha, beta-methylene]diphosphate. These data offer in vivo estimates of enzyme kinetics that are useful in revealing enzyme behavior in their normal physiological environment and provide means of evaluating the action of pharmacological, physiological, and pathological modulators of enzyme activity, in vivo.
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PMID:Kinetics of pulmonary angiotensin-converting enzyme and 5'-nucleotidase in vivo. 609 4

The release of plasma-membrane-bound enzymes by phosphatidylinositol-specific phospholipase C obtained from Bacillus thuringiensis was investigated. Among the ectoenzymes of plasma membrane tested, alkaline phosphodiesterase I was released markedly from rat kidney cortex slices, in addition to alkaline phosphatase and 5'-nucleotidase. Other membrane-bound enzymes; alanine aminopeptidase, leucine aminopeptidase, dipeptidyl peptidase, leucine aminopeptidase, dipeptidyl peptidase IV, esterase and gamma-glutamyl transpeptidase could not be liberated from the treated slices. Alkaline phosphodiesterase I was released linearly from rat kidney slices with the concentration of phosphatidylinositol-specific phospholipase C, but little enzyme was released from rat liver slices. Alkaline phosphodiesterase I separated from kidney tissue with n-butanol still retained phosphatidylinositol and was transformed into a lower molecular weight form by phosphatidylinositol-specific phospholipase C. This suggests an important function for phosphatidylinositol in the binding of alkaline phosphodiesterase I to the plasma membrane of rat kidney cells. The alkaline phosphodiesterase I released from rat kidney had a molecular weight of about 240,000 and an isoelectric point (pI) of 5.4. The enzyme hydrolyzed the phosphodiester linkage of p-nitrophenyl-thymidine 5'-monophosphate at pH 8.9 and had a Km value of 0.3 mM. The enzyme was activated by Mg2+ and Ca2+, but was inhibited by EDTA. Strong inhibition took place on the addition of adenosine 5'-phosphosulfate or the nucleotide pyrophosphates, i.e., UDP-galactose and alpha, beta-methylene ATP.
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PMID:Release of alkaline phosphodiesterase I from rat kidney plasma membrane produced by the phosphatidylinositol-specific phospholipase C of Bacillus thuringiensis. 609 28

The glycogen-containing ascites cell line was found to have a 3-5 times higher 5'-nucleotidase specific activity than the glycogen-free variant, resulting in different substrate affinity constants of Km = 0.14 mM and Km = 0.69 mM respectively. These activity differences were due to true 5'-nucleotidase as shown by its inactivation through specific inhibitors such as concanavalin A and alpha, beta-methylene adenosine diphosphate. Substrate specificity of the enzyme was similar in both cell lines, but differences were observed with respect to the pH optimum and stability.
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PMID:Comparison of 5'-nucleotidase activities of isolated plasma membranes of two ascites cell variants. 609 86

The activity of plasma membrane marker enzymes which are involved in purine metabolism (5'-nucleotidase, alkaline 5'-nucleotide phosphodiesterase), in active ion transport (Na-K-Mg-adenosine triphosphatase, ouabain-sensitive Na-K-adenosine triphosphatase), in aminoacid transport (gamma-glutamyltranspeptidase), and in basic physiologic functions (alkaline phosphomonoesterase) were assayed in mononuclear cells isolated from peripheral blood of normal donors and of patients with primary immunodeficiency. Irrespective of the clinical classification of the immunodeficiency, the cells of patients were characterized by significantly diminished 5'-nucleotidase and to a certain extent by lower alkaline phosphomonoesterase activities. Average activity levels of other enzymes were similar in cells of patients and controls, but scattering was more pronounced in the first group. Determination of substrate affinity revealed different kinetic properties of 5'-nucleotidase in cells from patients and normal donors; however, the extent of inhibition by beta-glycerophosphate or alpha, beta-adenosine-methylene diphosphate was comparable for both types of cells. The presence of inhibitory compounds in patients' serum was excluded by mixing experiments. When activities of the various plasma-membrane-associated enzymes were compared with each other, significant correlations emerged in normal lymphocytes. Most of these correlations were absent in cell membranes of immunodeficient patients. The findings indicate that the plasma membrane of lymphocytes from patients with immunodeficiency may be characterized by an altered distribution of enzymatic constituents.
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PMID:Correlations between enzymatic and immunologic properties of human peripheral blood mononuclear cells. I. Ectoenzymes of normal and immunodeficient peripheral blood mononuclear cells. 612 61

In the transversely cut rat hippocampus, adenosine caused a dose-dependent increase in the accumulation of [3H]cyclic AMP from [3H]ATP. Adenosine breakdown products were inactive. AMP was somewhat less effective than adenosine, and its effect could be partially, but not completely, abolished by alpha, beta-methylene-ADP and GMP, which inhibited its metabolism by 5'-nucleotidase. The effect of adenosine was unaffected by inhibitors of adenosine deaminase, but enhanced by several inhibitors of adenosine uptake. Some analogues of adenosine, including N6-phenylisopropyladenosine (PIA), 2-chloroadenosine and adenosine 5'-ethylcarboxamide (NECA), were more active than adenosine, whereas others such as 2-deoxyadenosine and 9-(tetrahydro-2-furyl)adenine (SQ 22536) actually inhibited the response. The effect of PIA was highly stereospecific. The action of adenosine was inhibited by several alkylxanthines, the most potent of which was 8-phenyltheophylline. [3H]Cyclohexyladenosine (CHA) bound specifically to cell membranes from the rat hippocampus. The extent of binding was similar to that found in other cortical areas. The relative potency of some adenosine analogues and alkylxanthines to displace labelled CHA was essentially similar to their potency as effectors of the cyclic AMP system. Adenosine contributed to the cyclic AMP-elevating effect of alpha-adrenoceptor-stimulating drugs and several amino acids, but not to that seen with isoprenaline. The cyclic AMP increase seen following depolarization was only partially adenosine-dependent. The present results demonstrate that the rat hippocampus contains adenosine receptors mediating cyclic AMP accumulation and that these receptors have similar characteristics to those mediating pyramidal cell depression. Adenosine-induced cyclic AMP accumulation may be used as a biochemical correlate to electrophysiology and as a convenient parameter to assess the influence of drugs on adenosine mechanisms in the rat hippocampus.
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PMID:Adenosine receptors mediating cyclic AMP production in the rat hippocampus. 612 48

Crude tissue or tumor extracts either do not contain sufficient inosine 5'-monophosphate dehydrogenase (IMPD) activity to be measured spectrophotometrically, or interfering enzyme activities prevent the use of a more sensitive radiochemical assay. A modified assay system which incorporates alpha, beta-methylene adenosine 5'-diphosphate, an inhibitor of 5'-nucleotidase; allopurinol, an inhibitor of xanthine oxidase; and ethylenediaminetetraacetate, an inhibitor of alkaline phosphatase, has been developed. [14C]Xanthine monophosphate produced during the assay was separated from [14C]hypoxanthine monophosphate by thin-layer chromatography on flexible diethylaminoethyl-cellulose sheets. Xanthine monophosphate formation was linear for at least 40 min and was inhibited by greater than 95% in the presence of mycophenolic acid, a specific IMPD inhibitor. Partial purified IMPD from murine EMT6 tumors was used to compare assay rates obtained with the radiochemical and spectrophotometric assays under identical conditions. The reaction rate of the radiochemical assay was 0.92 +/- 0.07 (S.E.) of the rate of xanthine monophosphate formation as determined spectrophotometrically at 290 nm, indicating that both assays are measuring product formation with an equal degree of accuracy. The improved radiochemical assay was used to determine IMPD specific activity in supernatants from EMT6 tumors and several normal mouse tissues. The observed activities (nmol/min/mg protein) were: EMT6 tumor, 0.303; spleen, 0.029; brain, 0.022; kidney, 0.015; lung, 0.009; liver, 0.008; and heart and skeletal muscle, less than 0.004.
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PMID:Sensitive radiochemical assay for inosine 5'-monophosphate dehydrogenase and determination of activity in murine tumor and tissue extracts. 613 40

We applied a simple lead salt-based stain for interstitial and vascular 5'-nucleotidase to 150 muscle biopsy specimens. No reaction was obtained with 2'- or 3'-adenosine monophosphate, indicating that the stain was specific, and distinct from phosphatases. Staining was not inhibited by alpha, beta-methylene adenosine 5'-diphosphate, but was prevented by formaldehyde fixation or by brief immersion in octoxynol 9 (Triton X-100). Nucleotidase stains the following specific histologic sites that distinguish it from alkaline phosphatase: the intima and adventitia of medium-sized and large arteries, perineural and muscle spindle sheaths, and tendon insertions. Aside from these structures, normal muscle shows little reaction, as the sarcoplasm and sarcolemma do not stain. Neither of these enzymes shows a compensatory increase, histochemically, in myo-adenylate deaminase deficiency. In Duchenne's muscular dystrophy, however, and particularly in inflammatory myopathy, interstitial staining of 5'-nucleotidase is increased, leading to investment of most muscle fibers in the affected area. The stain rarely identifies regenerating fibers. Although alkaline phosphatase commonly shows a corresponding increase in interstitial staining, we encountered six cases of inflammatory myopathy in which this was absent, despite pronounced endomysial staining in the 5'-nucleotidase reaction. 5'-Nucleotidase thus appears to provide a valuable adjunct in the diagnosis of inflammatory myopathy.
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PMID:Interstitial 5'-nucleotidase stain for frozen biopsy specimens of skeletal muscle. A useful adjunct in the diagnosis of polymyositis. 619 1

Adenine nucleotides cause adenosine receptor-mediated increases in cyclic AMP in the VA13 human fibroblast line. Levels of adenosine accumulated in the medium are insufficient to account for the responses to adenine nucleotides. Since rapid conversion of the nucleotides to adenosine by 5'-nucleotidase in the vicinity of the receptor might account for the responses, six experimental methods were developed to distinguish between "local conversion" and direct action of the nucleotides. Results of all six methods favored local conversion. (1)5'-Nucleotidase inhibitors blocked the accumulations of cyclic AMP elicited by AMP, ADP, and ATP, but did not affect the response to adenosine. The most potent inhibitor of both conversion of AMP and response to AMP was alpha, beta-methylene-ADP (APCP). (2) Adenosine deaminase blocked the responses to AMP, ADP, ATP, and adenosine-containing coenzymes. (3) Theophylline, a specific competitive adenosine antagonist, was an insurmountable inhibitor of the increases in cyclic AMP caused by AMP, ADP, and ATP. The insurmountability was presumably due to substrate saturation of the converting enzyme 5'-nucleotidase. (4) Although ADP and ATP had partial agonist-liked dose-response curves, they did not inhibit the response to adenosine. (5) Nine cell lines which responded to adenosine were tested for response to AMP. Cell lines with high levels of 5'-nucleotidase had large responses to AMP, those with intermediate levels of 5'-nucleotidase had large or intermediate responses to AMP, and those with low 5'-nucleotidase levels did not respond to AMP. (6) Inhibition of the uptake of labelled adenosine was used as an indicator of unlabelled adenosine concentrations near the cell membrane. Unlabelled AMP inhibited uptake nearly as effectively as unlabelled adenosine. APCP reversed the inhibition by AMP but not the inhibition by adenosine. The adenosine receptor is concluded to be an entity distinct from adenine nucleotide receptors.
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PMID:Adenosine receptor activation by adenine nucleotides requires conversion of the nucleotides to adenosine. 626 30


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