Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.11.11 (AMPK)
 12,425 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Cyclic nucleotide levels, protein phosphotransferase activities, and cyclic nucleotide-binding proteins have been determined and partially characterized in the mouse lymphosarcoma P1798. This system is used as a model to understand the function of these activities in a rapidly proliferating cell. Adenosine 3':5'-monophosphate (cAMP) concentrations are 5-fold higher in the lymphosarcoma cells than in thymocytes. In both the thymocytes and malignant tissue, cAMP concentrations are increased by physiological concentrations of epinephrine and prostaglandin. The guanosine 3':5'-monophosphate (cGMP) level in the lymphosarcoma is 0.1 pmole/10(6) cells and is not modified by acetylcholine, prostaglandin F2alpha, or concanavalin A. Four protein phosphotransferase activities have been identified in the lymphosarcoma. These are the cAMP-dependent protein kinase type I and II isozymes and a "histone kinase" and a "phosvitin kinase"; neither of the latter two is regulated by cyclic nucleotides. Characterization of these enzymes was based on fractionation by DE 52 chromatography, substrate specificity, interaction with the protein inhibitor of cAMP-dependent protein kinases, and sucrose gradient sedimentation rates. Both the cAMP-dependent protein phosphotransferase activity and the phosvitin phosphotransferase activity are 2-to 4-fold elevated in the lymphosarcoma cells in comparison to thymocytes. cAMP binding is associated with both the type I and II isozymes and with a fraction tentatively designated as the regulatory subunit of these enzymes. cGMP also binds to this later fraction and to the partially purified fraction containing the type IcAMP-dependent enzyme. The histone phosphotransferase activity of this fraction is also stimulated by cGMP, but studies of the number of binding sites and of absorption to cAMP and cGMP affinity resins indicated that this fraction contains more than one species of cyclic nucleotide-binding protein.
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PMID:Protein phosphotransferase activities and cyclic nucleotide action in proliferating lymphocytes. 18 45

Ovarian follicles of Xenopus laevis frogs consist of a single large oocyte surrounded by follicle cells attached to the oocyte by gap junctions. Adenosine has been found to activate an outward K+ current in follicles. This response is reduced by microinjection of protein kinase inhibitor (PKI), suggesting that adenosine 3',5'-cyclic monophosphate (cAMP) mediates the response. To investigate this further, we verified previous studies that indicate that several methods of elevating cAMP in follicles activate hyperpolarizing outward currents. The potency of two adenosine analogues to hyperpolarize follicles, 5'-N-ethylcarboxamidoadenosine (NECA) greater than cyclopentyladenosine, is indicative of A2 receptors that are characteristically coupled to adenylyl cyclase. We also report for the first time that another stimulator of adenylyl cyclase, follicle-stimulating hormone (FSH), also induces a hyperpolarizing current in follicles which is carried by K+ and attenuated by injection of PKI. We used a novel procedure to completely remove follicle cells from oocytes. Intact follicles, but not oocytes completely stripped of follicle cells, hyperpolarized in response to FSH, NECA, dibutyryl cAMP, microinjected cAMP, and forskolin, but not to dideoxyforskolin (which does not activate adenylyl cyclase). Injection of the catalytic subunit of cAMP-dependent protein kinase (which is too large to traverse gap junctions) into oocytes of intact follicles failed to activate a K+ current. These data suggest that FSH and adenosine hyperpolarize follicles by stimulating adenylyl cyclase and that cAMP-dependent protein kinase must be activated on both sides of follicle cell-oocyte gap junctions to elicit a hyperpolarizing K+ current.
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PMID:Xenopus oocyte K+ current. I. FSH and adenosine stimulate follicle cell-dependent currents. 212 36

(Rp)-Adenosine 3',5'-monophosphorothioate ((Rp)-cAMPS) is a highly specific antagonist of the cAMP-dependent protein kinase from eukaryotic cells and is a very poor substrate for phosphodiesterases. It is therefore a useful tool for investigating the role of cAMP as a second messenger in a variety of biological systems. Taking advantage of stereospecific inversion of configuration around the alpha-phosphate during the adenylate cyclase reaction, we have developed a method for the preparative enzymatic synthesis of the Rp diastereomer of adenosine 3',5'-monophosphorothioate ((Rp)-cAMPS) from the Sp diastereomer of adenosine 5'-O-(1-thiotriphosphate) ((Sp)-ATP alpha S). The adenylate cyclase from Bordetella pertussis, partially purified by calmodulin affinity chromatography, cyclizes (Sp)-ATP alpha S approximately 40-fold more slowly than ATP, but binds (Sp)-ATP alpha S with about 10-fold higher affinity than ATP. The triethylammonium salt of the reaction product can be purified by elution from a gravity flow reversed-phase C18 column with a linear gradient of increasing concentrations of methanol. Yields of the pure (Rp)-cAMPS product of a synthesis with 2 mg of substrate are about 75%.
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PMID:Enzymatic synthesis of the cAMP antagonist (Rp)-adenosine 3',5'-monophosphorothioate on a preparative scale. 217 77

Hypoxanthine and adenosine are present in preparations of mouse ovarian follicular fluid, and these purines maintain mouse oocytes in meiotic arrest in vitro (Eppig et al.: Biology of Reproduction 33:1041-1049. 1985). The first hypothesis tested in this study is that purines which maintain meiotic arrest act by maintaining meiosis-arresting levels of cyclic adenosine monophosphate (cAMP) in the oocyte. Oocyte-cumulus cell complexes were incubated in control medium (no added purines), or medium containing 0.75 mM adenosine, 4 mM hypoxanthine, or both for 3 hr and the percentage of the oocytes that underwent germinal vesicle breakdown (GVB) and the cAMP content of the intact complexes and the oocytes were determined. Adenosine alone had little inhibitory effect on GVB at this time point but sustained higher levels of cAMP in the oocytes. Hypoxanthine maintained 80% of cumulus cell-enclosed oocytes in meiotic arrest and also sustained higher cAMP levels in the oocytes. The addition of adenosine to hypoxanthine-containing medium increased the percentage of oocytes maintained in meiotic arrest, and increased the amount of cAMP in the oocytes above that maintained by either hypoxanthine or adenosine alone. Neither hypoxanthine, adenosine, nor hypoxanthine plus adenosine altered the cAMP content of intact complexes when assayed after 3 hr culture. Microinjection of an inhibitor of the catalytic subunit of cAMP-dependent protein kinase induced GVB in denuded oocytes cultured in medium containing hypoxanthine. This purine, therefore, maintained meiotic arrest by sustaining elevated cAMP levels within the oocytes. The second hypothesis tested in this study is that purines maintain meiosis-arresting levels of cAMP, at least in part, by inhibiting cAMP phosphodiesterase activity. In descending order of potency, 3-isobutyl-1-methylxanthine (IBMX), guanosine, hypoxanthine, adenosine, and xanthosine inhibited cAMP phosphodiesterase in oocyte lysates. Moreover, like the potent phosphodiesterase inhibitor IBMX, hypoxanthine augmented the meiotic arrest and cAMP accumulation mediated by follicle-stimulating hormone (FSH) in intact complexes. Therefore, inhibition of oocyte phosphodiesterase appears to be one mechanism by which the purines could maintain meiosis-arresting levels of cAMP.
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PMID:Maintenance of meiotic arrest in mouse oocytes by purines: modulation of cAMP levels and cAMP phosphodiesterase activity. 247 69

The properties of adenosine inhibition of catecholamine-induced responses were investigated, using an isolated rat heart preparation. Perfusion of hearts with 0.1 microM isoproterenol increased myocardial cAMP content 2.8-fold, activation of cAMP-dependent protein kinase 4.4-fold, phosphorylase a formation 3.4-fold, left ventricular pressure 1.8-fold, rate of ventricular pressure development 2.1-fold, and rate of ventricular relaxation 2.2-fold within 1 minute. When perfused with the isoproterenol, 10 microM adenosine reduced the catecholamine-produced increase in cAMP, cAMP-dependent protein kinase, and phosphorylase by 30-40%, and the elevation in left ventricular pressure and rate of ventricular pressure development by 40-70% within 40 seconds. More than 2 minutes were required for the nucleoside to significantly reduce the isoproterenol-elicited increase in the rate of ventricular relaxation. Perfusion of adenosine alone at concentrations from 0.1 to 10 microM were without effect on the above parameters. Theophylline at 50 microM had no effect alone on the above parameters but blocked the inhibitory actions of adenosine on the isoproterenol-induced responses. In the presence of 15 mM Mg++ adenosine reduced by approximately 56% the 2-fold increase in myocardial membrane adenylate cyclase activity produced by 1 microM isoproterenol without affecting basal or fluoride-stimulated activity. Adenosine also reduced the isoproterenol-induced increase in enzyme activity assayed at 1-2 mM Mg++, a level that more closely approximates the intracellular activity of the ion. The results suggest that physiological concentrations of adenosine attenuate the catecholamine-induced increase in cAMP content, cAMP-dependent protein kinase activation, phosphorylase a formation, and contractile parameters in the working heart, via reducing the beta-adrenergic activation of adenylate cyclase.
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PMID:Mechanism of adenosine inhibition of catecholamine-induced responses in heart. 629 29

Whole-cell patch-clamp recordings from Vicia faba mesophyll protoplasts reveal that outward K+ current is increased in a dose-dependent fashion by intracellular application of cAMP. The enhancement of the outward current by cAMP is specific and it cannot be mimicked by a series of nucleotides that includes AMP, cGMP, and GMP. The enhancement is evoked by micromolar concentrations of cAMP in the presence of the phosphodiesterase inhibitor 3-isobutyl-1-methyl-xanthine. PKI or Walsh inhibitor, a specific peptide inhibitor of cAMP-dependent protein kinase (PKA), inhibits the outward K+ current. Adenosine 3',5'-phosphothioate, a competitive inhibitor of PKA, has a similar effect. Conversely, the catalytic subunit of PKA (cAMP independent) from bovine brain enhances the magnitude of the outward K+ current in the absence of added cAMP. Our results indicate that cAMP modulates K+ channel activity in mesophyll cells and suggest that this modulation occurs through a cAMP-regulated protein kinase.
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PMID:Cyclic AMP stimulates K+ channel activity in mesophyll cells of Vicia faba L. 752 28

Adenosine activates adenylate cyclase and phospholipase C in mast cells and potentiates stimulated mediator release. To determine whether activation of adenylate cyclase is necessary for the effects of adenosine on the mast cell secretory process, a specific inhibitor of cAMP-dependent protein kinase, KT5720, was used. Antigen and adenosine each induced a rapid increase in mast cell cAMP-dependent protein kinase activity within 30 s. Preincubation with KT5720 (100 nM-10 microM) suppressed cAMP-dependent protein kinase activity and inhibited antigen-stimulated beta-hexosaminidase and leukotriene C4 releases. Adenosine retained its ability to potentiate beta-hexosaminidase release in antigen- and A23187-stimulated cells even in the presence of complete cAMP-dependent protein kinase inhibition. Mast cells rendered unresponsive to adenosine-related signals by preincubation with adenosine analogs maintained this hyporesponsiveness after incubation with KT5720. It appears that the abilities of adenosine to augment mast cell degranulation and induce receptor hyporesponsiveness are independent of changes in cAMP.
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PMID:Inhibition of protein kinase A fails to alter mast cell adenosine responsiveness. 774 Oct 46

Adenosine is released in the brain in significant quantities in response to increased cellular activity. Adenosine has been shown either to decrease synaptic transmission or to produce an excitatory response in hippocampal synapses, resulting in increased glutamate release. Previous reports have shown that adenosine or its analogs reduced Ca2+ current in dorsal root ganglion and hippocampal neurons. Here we show that the selective activation of adenosine receptor subtypes has different effects on Ca2+ channels from acutely isolated pyramidal neurons from the CA3 region of guinea pig hippocampus. Activation of A1 receptors inhibited primarily N-type Ca2+ current. In contrast, activation of A2b receptors resulted in significant potentiation of P-type but not N-type Ca2+ current. This potentiation could be inhibited by blocking the cAMP-dependent protein kinase. Because of the ubiquity of adenosine, the differential effects on Ca2+ channels of adenosine receptor subtype activation may have significant implications for neuronal excitability.
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PMID:Differential activation of adenosine receptors decreases N-type but potentiates P-type Ca2+ current in hippocampal CA3 neurons. 838 1

We studied how extracellular cyclic AMP (cAMP) dilates the isolated and perfused canine coronary artery using pharmacological tools. Single injections of cAMP (1-1000 nmol), adenosine 3',5'-cyclic monophosphorothioate Sp-isomer (Sp-cAMPS) (10-1000 nmol, an agonist of the cell surface cAMP receptor in Dictyostelium discoideum and of cAMP-dependent protein kinase), adenosine (0.1-1000 nmol) and 5'-AMP (0.1-1000 nmol) dilated the canine coronary artery dose dependently. The potency order for vasodilation was adenosine > 5'-AMP > cAMP > Sp-cAMPS > 8-bromo-cyclic GMP > 3'-AMP > 8-bromo-cAMP > N6,O2'-dibutyryl-cAMP. 2'-Deoxy-cAMP, 2',3'-cAMP, guanosine, cGMP, 3'-GMP and 5'-GMP did not produce vasodilation. Adenosine antagonists such as aminophylline (1-100 microM, nonselective), 8-phenyltheophylline (0.1-10 microM, A1 selective), 8-cyclopentyl-1,3-dipropylxanthine (0.01-1 microM, A1 selective) and 3,7-dimethyl-1-proparglyxanthine (0.01-1 microM, A2 selective) shifted the dose-response curve of adenosine in parallel to the right, but they shifted that of cAMP to the right and downwards. 8-Phenyltheophylline (1 and 10 microM) inhibited the response to Sp-cAMPS (100 nmol) dose dependently. Aminophylline (10 microM) did not affect isoproterenol- and forskolin-induced vasodilations. Adenosine deaminase (3 U/ml) completely inhibited the response to adenosine, but not those to 5'-AMP, cAMP, 8-bromo-cAMP and Sp-cAMPS. 5'-Nucleotidase inhibitors, adenosine-5'-(alpha,beta-methylene) diphosphate (10 microM) and 5'-GMP (1 mM), inhibited the responses to cAMP and 5'-AMP, but not that to adenosine.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Pharmacological analysis of vasodilation induced by extracellular adenosine 3',5'-cyclic monophosphate in the isolated and perfused canine coronary artery. 838 43

The mechanism by which the endogenous vasodilator adenosine causes ATP-sensitive potassium (KATP) channels in arterial smooth muscle to open was investigated by the whole-cell patch-clamp technique. Adenosine induced voltage-independent, potassium-selective currents, which were inhibited by glibenclamide, a blocker of KATP currents. Glibenclamide-sensitive currents were also activated by the selective adenosine A2-receptor agonist 2-p-(2-carboxethyl)-phenethylamino-5'-N- ethylcarboxamidoadenosine hydrochloride (CGS-21680), whereas 2-chloro-N6-cyclopentyladenosine (CCPA), a selective adenosine A1-receptor agonist, failed to induce potassium currents. Glibenclamide-sensitive currents induced by adenosine and CGS-21680 were largely reduced by blockers of the cAMP-dependent protein kinase (Rp-cAMP[S], H-89, protein kinase A inhibitor peptide). Therefore, we conclude that adenosine can activate KATP currents in arterial smooth muscle through the following pathway: (i) Adenosine stimulates A2 receptors, which activates adenylyl cyclase; (ii) the resulting increase intracellular cAMP stimulates protein kinase A, which, probably through a phosphorylation step, opens KATP channels.
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PMID:Adenosine activates ATP-sensitive potassium channels in arterial myocytes via A2 receptors and cAMP-dependent protein kinase. 861 17


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