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:3.5.4.17 (adenosine deaminase)
5,206 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Adenylate deaminase (AMP aminohydrolase, EC 3.5.4.6) from lugworm (Arenicola cristata) body-wall muscle was partially purified by extraction in KCl solutions and chromatography on phosphocellulose. Enzyme activity was eluted from the column at two salt concentrations. Both forms show co-operative binding of AMP (Hill coefficient, h, 2.85) with s0.5 values of 20 mM and 15.6 mM. ATP and ADP act as positive effectors lowering h to 1.07 and s0.5 to 2mM. The apparent Ka (activation) for ATP was 1.5mM. GTP is an inhibitor with an apparent Ki of 0.12 mM. In vivo the ATP-activated adenylate deaminase is in the active form and may be regulated by changes in GTP concentrations. Adenylate deaminase may act as a primary ammonia-forming enzyme in ammonotelic marine invertebrates with the purine nucleotide cycle.
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PMID:Adenosine triphosphate-activated adenylate deaminase from marine invertebrate animals. Properties of the enzyme from lugworm (Arenicola cristata) body-wall muscle. 1 38

Conversion of adenosine to inosine is decreased in adenosine deaminase (ADA)-deficient fibroblasts at all concentrations of adenosine tested. Adenosine is not differentially toxic to ADA-deficient fibroblasts except at very high (5 X 10(-4) -1 X 10(-3) M) adenosine levels. Conversion of [14C] adenosine to GTP is not decreased in ADA-deficient cells compared with control cell strains. Adenosine conversion to ATP is the same as that in mutant cells except at high nonphysiologic concentrations, at which it is slightly decreased in ADA-deficient fibroblasts. This effect is probably not related to the biochemical pathology of ADA-deficient lymphocytes in vivo. Uridine, a pyrimidine compound, "rescues" control cells from the effects of adenosine toxicity, as previously reported, but it has no protective effect on ADA-deficient fibroblasts. This suggests that uridine will have no therapeutic role in the treatment of the ADA-deficient form of severe combined immunodeficiency (SCID) disease.
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PMID:Purine dysfunction in cells from patients with adenosine deaminase deficiency. 13 30

Ehrlich ascites tumor cells containing radioactive ATP were incubated in vitro with a range of concentrations of 2-deoxyglucose in order to produce different rates of ATP catabolism. Concentrations of all radioactive products of ATP catabolism were measured, and apparent rates of adenylate deaminase and inosinate dehydrogenase and of adenylate and inosinate dephosphorylation were calculated. It was concluded that these processes were reggulated primarily by the rate of formation of substrate, and to a lesser extent in some cases, by substrate concentration. No evidence was obtained for regulation of these processes by the concentration of ATP. The deoxyglucose-induced catabolism of radioactive GTP was also studied. When ATP catabolism was induced by incubation with 2,4-dinitrophenol, time courses of accumulation of purine nucleoside monophosphates and rates of alternative pathways of their metabolism were quite different than when deoxyglucose was used.
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PMID:Studies of the regulation of purine nucleotide catabolism. 16 83

Steroidogenesis by Y-1 adrenal tumor cells in culture is stimulated by ATP, adenyl-5'-yl imidodiphosphate (App(NH)), adenosine 5'(beta, alpha-methylene)triphosphate (App(CH2)p), ADP, AMP, NAD, FAD, and adenosine but not by adenine or other nucleoside triphosphates. ATP, App(NH)p, App(CH2)p, and adenosine are active in the micromolar range. Like adrenocorticotropic hormone (ACTH), the onset of stimulation is immediate and occurs to the same extent. Also active are 2'- and 5'-deoxyadenosine and 2-chloroadenosine whereas adenine xyloside, L-riboside, or arabinoside have very low activity. Stimulation is accompanied by rounding of the cells. Dipyridamole, an inhibitor of adenosine transport, increased the response to low concentrations of adenosine, suggesting that adenosine acts externally. Stimulation of steroidogenesis by adenosine or phosphorylated adenosine compounds fails to occur in the presence of crystalline adenosine deaminase, and the effect of the enzyme on adenosine, ATP, or NAD stimulation is reversed by the competitive inhibitor erythro-9-[3-(nonane-2-ol)]adenine. This suggests that the enzyme acts specifically on adenosine and a requirement for the conversion of the above compounds to adenosine seems probable. The inhibition of cAMP effects by adenosine deaminase suggests that some of its effects are also mediated by conversion to adenosine. Similar stimulation is seen in I-10 Leydig tumor cells, but an ACTH-resistant mutant of Y-1 cells, called OS-3, is relatively resistant to adenosine. Adenosine and 2-chloroadenosine stimulate adenylate cyclase in membranes from Y-1 and I-10 cells at concentrations slightly greater than are effective for steroidogenesis. Other nucleosides are ineffective. Like the NH2-terminal 24 residues of adrenocorticotropic hormone (1-24 ACTH), the adenosine effect in Y-1 membranes is rapid and is on the Vmax intercept (versus ATP) and not on the Km. In contrast to steroidogenesis, adenosine is only a partial agonist for adenylate cyclase. It effect occurs in the presence of ITP, GTP, or guanyl-5'-yl imidodiphosphate (Gpp(NH)p). Theophylline inhibits adenosine-stimulated steroidogenesis. Inhibition of adenylate cyclase occurs in the same concentration range but is of the mixed type.
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PMID:Activation of steroidogenesis and adenylate cyclase by adenosine in adrenal and Leydig tumor cells. 18 24

Adenylate deaminase from rat skeletal muscle has been studied with the objective of understanding how the activity of the enzyme is regulated in vivo. ATP and GTP inhibit the enzyme at low concentrations in the presence of 150 mM KCl. The ATP inhibition is reversed as the ATP concentration is raised to physiological levels. The GTP inhibition is reversed as the GTP concentration is raised to unphysiologically high levels. In the presence of physiological concentrations of ATP, the GTP inhibition is also greatly diminished, but inhibition by orthophosphate remains strong. The apparent affinities of the enzyme for GTP, ATP, and orthophosphate are reduced as the pH is decreased from 7.0 to 6.2. ADP also reduces the apparent affinities of the enzyme for the inhibitors. The regulatory effects of GTP, ATP, and ADP are produced primarily by their unchelated forms. Comparison of the kinetic behavior of the enzyme in vitro with metabolite concentrations in vivo indicates that the major variables that regulate the activity of adenylate deaminase of muscle in vivo are the concentrations of AMP, ADP, orthophosphate, and H+.
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PMID:Adenylate deaminase from rat muscle. Regulation by purine nucleotides and orthophosphate in the presence of 150 mM KCl. 47 76

Kinetic studies with adenylate deaminase have been performed by stopped flow methods at 20 degrees C in 0.01 M imidazole/HCl, pH 6.5. The data were analyzed using either the whole time course of the reaction or the initial portion of the full time course. At low KCl concentrations, activation by the product IMP complicates any interpretation. In the presence of 0.15 M KCl, the results are interpreted in terms of three types of purine nucleotide binding sites: an active site, an inhibitory site which appears to be relatively specific for nucleoside triphosphates, and an activating site which shows relatively little specificity for nucleoside phosphates. Nucleotide binding to the activating site weakens binding to the inhibitory site. Sigmoidal kinetic data observed as a function of AMP in the presence of the inhibitor GTP are interpreted in terms of AMP binding to the activating site and weakening GTP binding. A fragment of myosin, subfragement-2, which has previously been shown to form a tight complex with adenylate deaminase (Ashby, B., and Frieden, C. (1977) J. Biol. Chem. 252, 1869--1875) activates the deaminase reaction only slightly. Complex formation, however, makes the reaction less susceptible to inhibition by GTP, although high levels of this nucleotide will disrupt the complex. In the presence of GTP or GTP plus subfragment-2, hysteretic effects are observed.
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PMID:Adenylate deaminase. Kinetic and binding studies on the rabbit muscle enzyme. 72 7

Guanine nucleotides such as guanosine 5'-(3-O-thio)triphosphate (GTP gamma S) have been found to increase the binding of antagonists to adenosine A1 receptors. This response can be attributed either to a direct effect of GTP on receptors to increase antagonist affinity or to an indirect effect to decrease the affinity of receptors for a pool of endogenous adenosine that cannot be readily removed from membranes. In this study, adenosine content was measured in preparations of membranes and 3-[(3-cholamidopropyl)dimethylamino]-1-propanesulfonate (CHAPS)-solubilized receptors by a sensitive radioimmunoassay. In both preparations, pools of adenosine (2.5-10 pmol/mg of protein) were detected that were resistant to deamination by added adenosine deaminase (0.5-3 units/ml) unless membrane lipids were first dissolved in acetone. Electron microscopic examination of crude CHAPS-solubilized receptors revealed the existence of small vesicles (< 1 microns in diameter). Furthermore, most "solubilized" receptors were retained by a 0.1-microns filter. The effects of GTP gamma S were evaluated on the binding of an antagonist, 3-(4-amino-3-125I-phenethyl)-1-propyl-8-cyclopentylxanthine (125I-BW-A844U), to A1 receptors of bovine brain membranes, receptors solubilized in CHAPS (crude solubilized), or receptors partially co-purified with G proteins by agonist affinity chromatography (partially purified). GTP gamma S (10 microM) increased antagonist binding to membranes (20-50%) and crude CHAPS-solubilized receptors (> 200%) but increased binding to partially purified receptors by only 10-15%. GTP gamma S decreased agonist (125I-N6-aminobenzyladenosine) binding and increased antagonist Bmax, but did not significantly decrease (5%) the dissociation rate of the antagonist. Omission of Mg2+ mimicked the effects of GTP gamma S on agonist and antagonist binding and increased both the association and dissociation rates of 125I-BW-A844U. These data suggest that a Mg(2+)-dependent GTP gamma S-induced increase in antagonist binding to membranes and solubilized receptors is primarily due to unmasking of cryptic binding sites occupied by contaminating vesicular adenosine. These findings are consistent with the observation that adenosine receptor antagonists have been found to have little or no inverse agonist physiological effects in well oxygenated tissues.
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PMID:Indirect effect of guanine nucleotides on antagonist binding to A1 adenosine receptors: occupation of cryptic binding sites by endogenous vesicular adenosine. 143 51

Adenosine deaminase (ADA) was partially purified 486- and 994-fold from rat liver mitochondria and cytosol, respectively. Relative molecular mass of the enzymes from both fractions was 34,000. Km for adenosine and 2'-deoxy-adenosine were 3.08 x 10(-5) M and 3.03 x 10(-5) M for mitochondrial ADA and 3.12 x 10(-5) M and 2.87 x 10(-5) M for cytosolic ADA. The enzyme from both subcellular fractions had the maximum activity at pH 7.5-8.0, and pI 5.2 and 4.2 for mitochondrial and cytosolic enzyme, respectively. The enzyme was inhibited by erythro-9-(2-hydroxy-3-nonyl)adenine and 2'-deoxycoformycin with Ki 4.4 x 10(-7) M and 3.2 x 10(-7) M for mitochondrial ADA and 4.9 x 10(-7) M 2.8 x 10(-7) M for cytosolic ADA. Among the natural nucleoside and deoxynucleotide derivatives tested, deoxy-GTP and UTP inhibited only cytosolic adenosine deaminase by 60% and 40%, respectively.
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PMID:Adenosine deaminase: physical and chemical properties of partially purified mitochondrial and cytosol enzyme from rat liver. 144 46

Effects of adenosine and nucleotides on the release of previously stored [3H]-noradrenaline were studied in rabbit brain cortex slices. The slices were stimulated twice, in most experiments by 6 electrical field pulses delivered at 100 Hz. Adenosine and the nucleotides AMP, ADP, ATP, AMPS, ADP beta S, ATP gamma S, beta,gamma-imido-ATP and beta,gamma-methylene-ATP all reduced the evoked overflow of tritiated compounds. For purines for which concentration-response curves were determined, the order of potency was adenosine greater than ATP approximately ATP gamma S approximately beta,gamma-imido-ATP approximately ADP greater than beta,gamma-methylene-ATP. AMP 30 mumol/l and AMPS 30 mumol/l were approximately equieffective with 30 mumol/l of adenosine and ATP gamma S, and ADP beta S 30 mumol/l was approximately equieffective with 30 mumol/l of ADP. alpha,beta-Methylene-ADP, 2-methylthio-ATP, UTP and GTP gamma S did not change the evoked overflow of tritium. alpha,beta-Methylene-ATP caused an increase; however, the increase was small and became significant only after 59 min of exposure to alpha,beta-methylene-ATP or when the slices were stimulated by 30 pulses, 10 Hz. Neither adenosine deaminase (100 U/l) nor the blocker of 5'-nucleotidase, alpha,beta-methylene-ADP (10 mumol/l), attenuated the inhibition caused by ATP, ATP gamma S and beta,gamma-methylene-ATP, despite the fact that adenosine deaminase abolished the effect of adenosine. 8-Cyclopentyl-1,3-dipropylxanthine (DPCPX, 10 nmol/l) shifted the concentration-response curves of adenosine, ATP gamma S, beta,gamma-imido-ATP and beta,gamma-methylene-ATP to the right by very similar degrees. 8-(p-Sulphophenyl)-theophylline (30 and 300 mumol/l) also markedly antagonized the inhibition produced by ATP gamma S. alpha,beta-Methylene-ATP (10 and 30 mumol/l) and suramin (100 mumol/l) did not modify the effects of adenosine, ATP gamma S and beta,gamma-methylene-ATP. It is concluded that nucleotides themselves can inhibit the release of noradrenaline in the rabbit brain cortex. The nucleotides and adenosine seem to act at the same site, i.e., the A1 subtype of the P1-purinoceptor. The results support the notion that metabolically stable, phosphate chain-modified nucleotides such as ATP gamma S, beta,gamma-imido-ATP and beta,gamma-methylene-ATP can be potent P1 agonists. No evidence was found for presynaptic P2x-, P2y- or P3-purinoceptors.
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PMID:Stable adenine nucleotides inhibit [3H]-noradrenaline release in rabbit brain cortex slices by direct action at presynaptic adenosine A1-receptors. 144 82

The ability of brown fat cells isolated from control and cold-acclimated hamsters to respond to adenosine was investigated. In measurements of the rate of oxygen consumption, it was observed that cells from control hamsters responded as expected to addition of adenosine deaminase, 3-isobutyl-1-methylxanthine (IBMX), or 2-chloroadenosine (i.e., norepinephrine dose-response curves were shifted to left in presence of adenosine deaminase or IBMX and to right with 2-chloroadenosine). However, brown fat cells isolated from cold-acclimated hamsters, under identical conditions, showed almost complete absence of adenosine control. Thus acclimation to cold induced a desensitization to adenosine by physiological means. To evaluate the molecular mechanism underlying desensitization to adenosine, [3H]phenylisopropyladenosine ([3H]PIA) binding to brown fat membranes from control and cold-acclimated hamsters was investigated. [3H]PIA bound with similar high affinity (KD approximately 5 nM) and saturability (Bmax approximately 15 fmol/mg protein) in both membrane preparations, demonstrating that desensitization to adenosine was not due to changes in adenosine receptor number or receptor affinity for adenosine. Furthermore, GTP induced a reduction in [3H]PIA affinity in brown fat membranes from both control and cold-acclimated hamsters, indicating that desensitization was probably not due to an uncoupling between the receptor and Gi protein. It was therefore concluded that the adenosine desensitization process may be located at the Gi protein-adenylate cyclase interaction.
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PMID:Cold acclimation induces desensitization to adenosine in brown fat cells without changing receptor binding. 169 90


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