Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0027960 (mole)
 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Photo-switchable ion and enzyme sensors were fabricated by the use of glassy carbon electrode coated with nonactindoped or enzyme modified poly(vinyl chloride) (PVC) membranes. The ion sensor with nonactin-doped PVC membrane, which contained spirobenzopyran as the photosensitive dye, exhibited a potentiometric photoresponse to NH4+ ion in the solution. The dynamic range of the NH4+ ion sensor was 10(-7)--10(-3) M. Urea, adenosine, and asparagine sensors were prepared by coating the surface of the NH4+-ion sensor with urease, adenosine deaminase, and asparaginase membranes, respectively. These enzyme sensors could be used for determining the substrates at the micro mole level. The performance characteristics of these sensors were compared with those previously prepared membrane electrode sensors.
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PMID:Photo-switchable ion and enzyme sensors. Photoinduced potentiometric response of glassy carbon electrode coated with polymer or polymer/enzyme dual membrane. 263 77

It has been proposed that the pathogenesis of melanoma proceeds through multiple stages, ranging from benign proliferation of melanocytic cells to acquisition of the capacity to invade tissues and metastasize. During investigations of cell surface antigens expressed by melanocytes and melanoma, we identified an antigen system that was expressed by cultured normal melanocytes but not by melanoma cell lines. mAbs against this antigen detected a 120-kD cell surface glycoprotein on melanocytes. This molecule had been identified previously as the binding protein for adenosine deaminase (ADAbp). ADAbp was expressed by 51 melanocyte cell lines derived from normal fetal, newborn, and adult skin and adult choroid, but not by 102 melanoma cell lines derived from primary and metastatic lesions. Studies with radiolabeled bovine adenosine deaminase, confirmed that melanocytes expressed binding sites for adenosine deaminase, but no binding sites were detected on cultured melanoma cells. Further studies showed that ADAbp+ melanocytes became ADAbp- upon malignant transformation in vitro. Immunohistochemical studies on a panel of frozen tissues demonstrated reactivity of anti-ADAbp mAbs with epidermal melanocytes and benign junctional nevi, but not with potentially premalignant dysplastic nevi or primary/metastatic melanoma lesions. These studies demonstrate that ADAbp expression is lost with malignant transformation of melanocytes, presumably at an early stage in the transformation process.
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PMID:Cell surface antigens of human melanocytes and melanoma. Expression of adenosine deaminase binding protein is extinguished with melanocyte transformation. 289 80

Rat brain adenosine deaminase (E.C. 3.5.4.4.) was purified 667-fold from the supernatant fraction by the following techniques: heat treatment (60 degrees C), fractionation with ammonium sulfate, column chromatography on DEAE-Sepharose, and preparative gel electrophoresis. The purified enzyme was homogeneous by the criterion of polyacrylamide disc gel electrophoresis and isoelectric focusing. Amino acid composition is given. The isoelectric point of the enzyme (5.2) was determined by isoelectric focusing on agarose. The apparent molecular weight was estimated to be 39,000 (Stokes Radius [Rs] = 27.3 A) using a calibrated Sephacryl S-300 column. The study of the influence of the temperature on the initial reaction rates allowed calculation of Ea (8.9 Kcal/mole) and delta H (5.0 Kcal/mole) values. The variation of V and Km with pH suggests the existence of a sulfhydryl group and an imidazole group in the enzyme-substrate complex. The enzyme had a Km (adenosine) of 4.5 X 10(-5) M and was inhibited by inosine, guanosine, adenine, and hypoxanthine but not by other intermediates of purine metabolism. None of the inhibitors were active as substrates. The enzyme was also inhibited by dimethyl sulfoxide and ethanol. Inhibition by ethanol can account partially for the CNS depressant effects of levels 3 and 4 of alcohol intoxication. A number of drugs having therapeutic uses such as sedative, anxiolytic, analgesic, and relaxant are modulators of the enzyme. Among these, lidoflazine, phenylbutazone, and chlordiazepoxide are the most potent as inhibitors (Ki 30, 54, and 83 microM, respectively), whereas medazepam is the most potent as activator (Ka 0.32 mM). Thus, it is concluded that some drugs that inhibit adenosine uptake also modulate adenosine deaminase activity. Besides, since the enzyme is located extracellularly [Franco et al, 1986], these drugs can modulate the physiological effects exerted by extracellular adenosine.
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PMID:Purification and partial characterization of brain adenosine deaminase: inhibition by purine compounds and by drugs. 336 98

Analysis of the biological effects of specific DNA alkylations by simple alkylating agents is complicated by the variety of sites involved. It is, therefore, of value to be able to incorporate into cellular DNA nucleosides alkylated in a single position, e.g., O6-methyldeoxyguanosine. Such cellular incorporation is particularly difficult to achieve because this nucleoside is rapidly demethylated by adenosine deaminase. We have attempted to achieve such incorporation into the DNA of V79 cells by using coformycin, an inhibitor of adenosine deaminase, and by forcing the cells to depend on exogenous purines by the use of medium containing aminopterin. The DNA of V79 cells exposed to O6-methyl-[8-3H]deoxyguanosine (2.4 microM, sp. act. 14500 Ci/mole) showed an incorporation level of 4 X 10(-8) nucleotides. When 1000-fold higher concentrations were employed (3-15 mM, sp. act. 1.6 Ci/mole), significant cytotoxicity and inhibition of DNA synthesis was observed. However, because it was not economically feasible to administer high specific activity O6-methyldeoxyguanosine to the cells at these concentrations, we could not determine the amount of labeled nucleoside incorporated into DNA. Examination of the frequency of 6-thioguanine-resistant cells in these treated populations showed no significant increase above the background level. Comparison of the cytotoxic effect of O6-methyldeoxyguanosine with deoxyadenosine showed that the toxicity induced by O6-methyldeoxyguanosine could have resulted from mimicry of deoxyadenosine, rather than by incorporation of the alkylated nucleoside itself.
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PMID:Biological effects of incorporation of O6-methyldeoxyguanosine into Chinese hamster V79 cells. 668 81

1. Plasma and adipose tissue purine nucleosides were assayed by reversed phase high-performance liquid chromatography after purification of the samples on phenylboronate affinity gel. 2. The adenosine content of unstimulated subcutaneous adipose tissue was close to 1 n-mole/g. The concentrations of adenosine and inosine in canine arterial plasma were 0.26 +/- 0.03 and 0.16 +/- 0.03 microM, respectively. In venous plasma from the canine subcutaneous adipose tissue the corresponding values were 0.32 +/- 0.04 and 0.28 +/- 0.06 microM under basal conditions. The arterio-venous concentration difference of adenosine was linearly dependent upon the arterial adenosine concentration. At arterial concentrations below 0.3 microM there was a net production of adenosine; above 0.3 microM there was a net extraction of approximately 77% of the adenosine. Adenosine was extensively eliminated in blood. The major part of this elimination could be accounted for by metabolism to inosine, hypoxanthine and uric acid. 3. Following sympathetic nerve stimulation (4 Hz for 20 min) the rate of adenosine outflow from adipose tissue increased from 0.33 +/- 0.22 to a peak value of 1.2 +/- 0.26 n-mole/min. This corresponds to a net release of 8.7 +/- 3.0 n-mole/100 g tissue. Inosine outflow rose from 0.64 +/- 0.37 to 5.3 +/- 1.4 n-mole/min, corresponding to a net release of 24.6 4/- 8.7 n-mole/100 g. Nerve stimulation also increased the release of [3H]purines from [3H]adenine pre-labelled adipose tissue. The fractional release increased 15-fold after stimulation. The radioactivity was mainly in the form of hypoxanthine, inosine and uric acid while adenosine was a minor component. When metabolism in blood was inhibited by dipyridamole and an adenosine deaminase inhibitor nerve-stimulation-induced release of [3H]purines was mainly in the form of adenosine. 4. Noradrenaline injection also induced a release of radioactive purines and of inosine. On the other hand, the outflow of endogenous adenosine was very small. 5. The present results demonstrate that under basal conditions adenosine is present in arterial and venous canine plasma. The free extracellular tissue level may be similar to the basal arterial adenosine concentration. Sympathetic nerve stimulation and noradrenaline induces a marked release of adenosine which is rapidly metabolized in the tissue and blood stream to inosine, hypoxanthine and uric acid. In adipose tissue the levels of adenosine reached after adrenergic stimulation appear high enough to be of physiological relevance.
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PMID:The release of adenosine and inosine from canine subcutaneous adipose tissue by nerve stimulation and noradrenaline. 727 25

Binding of the transition state analogue coformycin and the ground state analogue 1-deaazadenosine to bovine adenosine deaminase have been thermodynamically characterized. The heat capacity changes for coformycin and 1-deazaadenosine binding are -4.7 +/- 0.8 kJ/mole-K and -1.2 +/- 0.1 kJ/mole-K, respectively. Since the predominant source of heat capacity change in enzyme interactions are changes in the extent of exposure of nonpolar amino acid side chains to the aqueous environment and the hydrophobic effect is the predominant factor in native structure stabilization, we propose that the binding of either class of ligand is associated with a stabilizing enzyme conformational change with coformycin producing the far greater effect. Analysis of the T dependence of the second order rate constant for formation of the enzyme/coformycin complex further reveals that the conformational change is not rate limiting. We propose that the enzyme may facilitate catalysis via the formation of a stabilizing conformation at the reaction transition state.
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PMID:Binding thermodynamics of the transition state analogue coformycin and of the ground state analogue 1-deazaadenosine to bovine adenosine deaminase. 1169 42

We have determined the stability curve of bovine adenosine deaminase via titrations with guanidine hydrochloride at pH = 6.3 from 5 to 65 degrees C. The data indicate that the enzyme undergoes an abrupt conformational transition at approximate, equals 29 degrees C, a finding supported by a temperature scan of the intrinsic enzyme fluorescence emission. Analysis of the data above and below this temperature with the modified Gibbs-Helmholtz equation allows for complete description of the equilibrium unfolding thermodynamics for either enzyme conformation. The high-temperature form of the enzyme is described by DeltaH degrees = 648 +/- 37 kJ/mole, DeltaC(P) = 23.2 +/- 2.5 kJ/mole-K, and a heat denaturational temperature T(h)(dn) = 72.5 +/- 0.9 degrees C. The low-temperature form is described by DeltaH degrees = 1284 +/- 47 kJ/mole, DeltaCP = 73.2 +/- 4.9 kJ/mole-K, and T(h)(dn) = 32.6 +/- 0.6 degrees C. Further thermodynamic analysis of the conformations that predominate at 38.3 degrees C, the bovine normal body temperature, and at 4 degrees C, where the crystals for x-ray structural analyses were formed, suggest that the stability of either form is due to favorable amino acid side chain nonpolar interactions with these interactions being much more optimized in the low-temperature conformation. We therefore conclude that the structure as determined by x-ray crystallographic methods cannot be the physiological structure. The data also suggest that the general calculation of enzyme stability curves from the extrapolation of heat denaturation data may inaccurately represent the enzyme stability as a low-temperature, nondenaturational transition is assumed not to exist. Further consequences in terms of general enzyme catalysis are also discussed.
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PMID:The stability curve of bovine adenosine deaminase is bimodal. 1243 75

Bovine adenosine deaminase undergoes a nondenaturational conformational change at 29 degrees C upon heating which is characterized by a large increase in heat capacity. We have determined the transition state thermodynamics of the conformational change using a novel application of differential scanning calorimetry (DSC) which employs very slow scan rates. DSC scans at the conventional, and arbitrary, scan rate of 1 degree C/min show no evidence of the transition. Scan rates from 0.030 to 0.20 degrees C/min reveal the transition indicating it is under kinetic control. The transition temperature T(t) and the transition temperature interval deltaT increase with scan rate. A first order rate constant k1 is calculated at each T(t) from k1 = r(scan)/deltaT, where r(scan) is the scan rate, and an Arrhenius plot is constructed. Standard transition state analysis reveals an activation free energy deltaG(double dagger) of 88.1 kJ/mole and suggests that the conformational change has an unfolding quality that appears to be on the direct path to the physiological-temperature conformer.
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PMID:Transition state characterization of the low- to physiological-temperature nondenaturational conformational change in bovine adenosine deaminase by slow scan rate differential scanning calorimetry. 1658 31