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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Release of adenosine and AMP into epicardial fluid and coronary venous effluent of isovolumic guinea-pig hearts was examined during normoxic (95% O2) and hypoxic (30% O2) perfusion with and without the ecto-5'-nucleotidase inhibitor alpha,beta-methylene adenosine diphosphate (AOPCP)*. Normoxic epicardial and venous adenosine levels were 221 +/- 27 and 67 +/- 11 nM, respectively, in untreated hearts. During 15 min of hypoxia, epicardial and venous adenosine levels increased in a phasic manner, reaching maximal values of 498 +/- 32 and 441 +/- 43 nM, respectively, during the initial 5 min of hypoxia. Epicardial and venous adenosine levels then declined slightly during the subsequent 10 min to 332 +/- 33 and 224 +/- 34 nM, respectively. Infusion of 50 microM AOPCP significantly reduced venous adenosine levels during normoxia (less than 50% of control), but was without effect on normoxic epicardial adenosine. Epicardial and venous adenosine levels increased during hypoxia with AOPCP but the increases were lower than those for untreated hypoxic hearts. Epicardial and venous adenosine levels recovered to baseline levels following 30 min of reoxygenation in both groups. Epicardial and venous AMP levels were elevated by AOPCP treatment during normoxia and hypoxia. Coronary vascular resistance decreased during hypoxia but the decline in resistance was less in AOPCP treated hearts. It is concluded that whereas basal interstitial adenosine levels appear to be independent of ecto-5'-nucleotidase activity, the hypoxic increase in interstitial adenosine is partially derived from an AOPCP sensitive ecto-5'-nucleotidase. Venous adenosine appears to be significantly dependent on ecto-5'-nucleotidase activity during normoxia and hypoxia.(ABSTRACT TRUNCATED AT 250 WORDS)
J Mol Cell Cardiol 1992 Mar
PMID:Myocardial adenosine formation during hypoxia: effects of ecto-5'-nucleotidase inhibition. 162 50

Acute myocardial ischaemia frequently is complicated by ventricular tachyarrhythmias. These arrhythmias are in part due to an increased susceptibility of myocardial cells to adenylyl cyclase stimulation by catecholamines [1]. As adenylyl cyclase underlies an endogenous dual regulation by stimulatory and inhibitory receptor systems, adenylyl cyclase stimulation can be counteracted by the activation of receptors like the muscarinic M2 receptor [2]. Therefore, the effect of myocardial ischaemia on muscarinic receptor and "inhibitory" guanine nucleotide binding proteins (G(i)) mediated inhibition of adenylyl cyclase was studied. During 5 min of myocardial ischaemia, carbachol mediated inhibition of forskolin and isoproterenol stimulated adenylyl cyclase was reduced by 30% and 50%, respectively. Hormone independent inhibition of adenylyl cyclase by the nonhydrolyzable GTP-analogue guanosine 5'-[beta gamma-imido]triphosphate (Gpp(NH)p) was reduced by 46%. In contrast, the amount of G(i), as determined by pertussis toxin catalyzed ADP-ribosylation, remained constant during 15 min of ischaemia. The impaired function of muscarinic receptor linked signal transduction during early myocardial ischaemia could contribute to the occurrence of ischaemia induced tachyarrhythmias by a reduced ability to counteract adenylyl cyclase activation.
J Mol Cell Cardiol 1992 May
PMID:Reduced adenylyl cyclase inhibition by carbachol and GTP during acute myocardial ischaemia. 163 72

A segment of the exotoxin A gene of Pseudomonas aeruginosa, coding for the N-terminal end of domain I and domain II of the toxin (ETA), was genetically fused to the diphtheria toxin gene of Corynebacterium diphtheriae, coding for the N-terminal end of A fragment of diphtheria toxin (DT). The resulting hybrid protein (termed CED1) was produced in large amounts and exported to the periplasm in Escherichia coli. This chimaeric protein reacted with both anti-ETA and anti-DT antisera. Furthermore, the chimaeric protein displayed ADP-ribosylation activity and exhibited cytotoxicity to mouse 3T6 fibroblasts. These results demonstrated that the chimaeric protein is cytotoxic, and that the toxic potential of DTA can be selectively internalized and translocated via domains I and II of exotoxin A, which are thus sufficient to direct and translocate an enzymatically active heterologous polypeptide segment into the cytosol of sensitive cells.
Mol Microbiol 1992 May
PMID:Cytotoxic activity of a recombinant chimaeric protein between Pseudomonas aeruginosa exotoxin A and Corynebacterium diphtheriae diphtheria toxin. 164 Aug 30

The effect of regucalcin, a calcium-binding protein isolated from rat liver cytosol, on Ca2+ transport in rat liver nuclei was investigated. Ca2+ uptake and release were determined with a Ca2+ electrode. Ca2+ uptake increased dependent on adenosine triphosphate (ATP; 0.5-2.0 mM), while the uptake was negligible in the presence of 2 mM ADP or AMP. Regucalcin (0.5-2.0 microM) had no effect on Ca2+ uptake following addition of 2.0 mM ATP. Meanwhile, Ca2+, which accumulated in the nuclei during 10 min after ATP addition, was significantly released by the addition of regucalcin. This release was dose-dependent (0.1-2.0 microM). Vanadate (100 microM) and guanosine triphosphate (100 microM) did not cause a significant release of Ca2+ from the nuclei. Trifluoroperazine (TFP; 50 microM), an antagonist of calmodulin, significantly increased Ca2+ release from the nuclei. The presence of regucalcin (0.5 microM) further enhanced the TFP effect. These results indicate that regucalcin stimulates Ca2+ release from liver nuclei, and that the effect is not influenced by calmodulin antagonist. The finding suggests that regucalcin can regulate the Ca2+ transport system in rat liver nuclei.
Mol Cell Biochem 1992 Jul 06
PMID:Effect of calcium-binding protein regucalcin on Ca2+ transport system in rat liver nuclei: stimulation of Ca2+ release. 164 Sep 37

Changes in the sensitivity of adenylyl cyclase observed in pig thyroid cells cultured 2 days in the presence of thyroid-stimulating hormone (TSH) or forskolin were assessed by examining the properties of Gs protein. Chronic treatment of thyroid cells with various concentrations of TSH (0.01-1 mU/ml) or forskolin (0.1-10 microM) increased the response of adenylyl cyclase to a further stimulation by forskolin or NaF + AlCl3 ([AlF4]-). In contrast, the enzyme activation promoted by guanosine 5'-(beta,gamma-imido) triphosphate (Gpp(NH)p) was markedly affected. There was a significant increase in adenylyl cyclase activation by Gpp(NH)p in membranes from cells treated with low concentrations of TSH (less than or equal to 0.1 mU/ml) or forskolin (less than or equal to 1 microM) but a significant decrease in membranes from cells cultured with a higher concentration of TSH (1 mU/ml) or forskolin (10 microM). This decrease in Gpp(NH)p-stimulated adenylyl cyclase activity was mimicked by 8-bromo-cAMP but not by 1,9-dideoxyforskolin, a forskolin analogue which has lost its ability to activate adenylyl cyclase. There was a good correlation with the ability of Gs protein to be ADP-ribosylated by cholera toxin: labeling of Gs protein decreased following chronic treatment of thyroid cells with TSH (1 mU/ml) or forskolin (10 microM). In contrast, under the same experimental culture conditions a slight but significant increase in the quantity of Gs subunits was observed by immunoblotting analysis.(ABSTRACT TRUNCATED AT 250 WORDS)
Mol Cell Endocrinol 1991 Feb
PMID:Alteration of the functional activity of Gs protein in thyrotropin-desensitized pig thyroid cells. 164 41

Shifting Escherichia coli from aerobic to anaerobic growth caused changes in the ratio of [ATP]/[ADP] and in negative supercoiling of chromosomal and plasmid DNA. Shortly after lowering oxygen tension, both [ATP]/[ADP] and supercoiling transiently decreased. Under conditions of exponential anaerobic growth, both were higher than under aerobic conditions. These correlations may reflect an effect of [ATP]/[ADP] on DNA gyrase, since in vitro [ATP]/[ADP] influences the level of plasmid supercoiling attained when gyrase is either introducing or removing supercoils. When the supercoiling activity of gyrase was perturbed by a mutation in gyrB, a shift to anaerobic conditions resulted in plasmid supercoil relaxation similar to that seen with wild-type. However, the low level of supercoiling in the mutant persisted during a time when supercoiling in wild-type recovered and then exceeded aerobic levels. Thus, changes in oxygen tension can alter DNA supercoiling through an effect on gyrase, and correlations exist between changes in supercoiling and changes in the intracellular ratio of [ATP]/[ADP].
J Mol Biol 1991 Jun 05
PMID:Bacterial DNA supercoiling and [ATP]/[ADP]. Changes associated with a transition to anaerobic growth. 164 92

The alpha subunit of the guanine nucleotide-binding regulatory protein GS mediates stimulation of adenylyl cyclase activity. This subunit, GS alpha, exists as two molecular weight forms, termed long and short, that differ by 14 or 15 amino acids. A physiological distinction between these two forms has yet to be defined. To compare the activities of these GS alpha isoforms, long and short forms of rat GS alpha were expressed in the cyc- variant of S49 murine lymphoma cells, which is deficient in endogenous GS alpha expression. By immunoblot analysis, the level of recombinant proteins in the clones expressing the long form of GS alpha was about twice that present in the clones expressing the short form of GS alpha or in the S49 wild-type cells. Both recombinant GS alpha proteins were sensitive to cholera toxin-catalyzed ADP-ribosylation, although the short form was labeled preferentially in both recombinant and S49 wild-type cell lines. In whole-cell assays, the clones expressing the long and short forms of GS alpha and the S49 wild-type cells gave comparable responses for stimulation of cAMP accumulation after challenge with (-)-isoproterenol, cholera toxin, or forskolin. In adenylyl cyclase assays with partially purified membranes, clones expressing the long form of GS alpha gave approximately twice the levels of cAMP in response to isoproterenol, guanosine-5'-O-(3-thio)triphosphate, NaF, or forskolin, compared with membranes from the clones expressing the short form of GS alpha or the S49 wild-type cells. However, when maximal adenylyl cyclase activity was normalized to the level of GS alpha protein in S49 wild-type cells, the cAMP productions were similar between all of the cell lines. In other membrane-based assays, the long and short forms of GS alpha were also equivalent in their dose response to isoproterenol and GTP, their kinetics of guanine nucleotide exchange and GTPase activity, and the induced high and low affinity states of the beta-adrenergic receptor in response to isoproterenol. In the latter radioligand binding analysis, membranes from the two clones expressing the long form of GS alpha consistently gave a greater proportion of the agonist high affinity state; however, this variation likely reflects the greater expression levels of GS alpha in these membranes. Thus, we conclude that the long and short forms of GS alpha expressed in S49 cyc- cells are very similar in their ability to stimulate adenylyl cyclase activity and to couple to beta-adrenergic receptors.
Mol Pharmacol 1991 Jun
PMID:Expression and characterization of the long and short splice variants of GS alpha in S49 cyc- cells. 164 45

The effect of glucocorticoid treatment of DDT1 MF-2 smooth muscle cells on the signaling via two adenosine receptors with opposing actions on cAMP generation was examined. Treatment with dexamethasone caused a dose- and time-dependent increase in the number of adenosine A1 receptors but did not affect the KD or the proportions of receptors in high and low affinity states. The EC50 was 1 nM dexamethasone, and maximal response was achieved after 24 hr. The number of receptors was increased by approximately 50%. Other steroid hormones, including aldosterone, progesterone, testosterone, and estrogen, were much less effective, and addition of the glucocorticoid receptor antagonist RU 486 or the protein synthesis inhibitor cycloheximide prevented the up-regulation, showing that the effect was mediated via a glucocorticoid receptor-specific mechanism that involves protein synthesis. In dexamethasone-treated cells the A1 receptor agonist (-)-N6-phenylisopropyladenosine [(R)-PIA] was 3 times more potent as an inhibitor of cAMP formation induced by isoprenaline than in untreated cells. ADP ribosylation of inhibitory GTP-binding proteins by pertussis toxin completely prevented (R)-PIA from inhibiting cAMP accumulation. A further analysis of the different GTP-binding proteins, including the three Gi subtypes (Gi1, Gi2, and Gi3), revealed no quantitative or qualitative change after dexamethasone treatment. In addition, the adenosine A2 receptors were down-regulated, as indicated by the fact that the ability of the A2 receptor agonist 5'-N-ethylcarboxamidoadenosine to increase cAMP formation was decreased by 20-30% in dexamethasone-treated cells. In summary, we have shown that A1 and A2 receptors on the same cell are differentially regulated by glucocorticoids and that this has functional importance in the regulation of cAMP accumulation.
Mol Pharmacol 1991 Aug
PMID:Glucocorticoid receptor activation leads to up-regulation of adenosine A1 receptors and down-regulation of adenosine A2 responses in DDT1 MF-2 smooth muscle cells. 165 51

An enzyme able to cleave dinucleoside triphosphates has been purified 3,750-fold from Saccharomyces cerevisiae. Contrary to the enzymes previously shown to catabolize Ap4A in yeast, this enzyme is a hydrolase rather than a phosphorylase. The dinucleoside triphosphatase molecular ratio estimated by gel filtration is 55,000. Dinucleoside triphosphatase activity is strongly stimulated by the presence of divalent cations. Mn2+ displays the strongest stimulating effect, followed by Mg2+, Co2+, Cd2+, and Ca2+. The Km value for Ap3A is 5.4 microM (50 mM Tris-HCl [pH 7.8], 5 mM MgCl2, and 0.1 mM EDTA; 37 degrees C). Dinucleoside polyphosphates are substrates of this enzyme, provided that they contain more than two phosphates and that at least one of the two bases is a purine (Ap3A, Ap3G, Ap3C, Gp3G, Gp3C, m7Gp3A, m7Gp3G, Ap4A, Ap4G, Ap4C, Ap4U, Gp4G, and Ap5A are substrates; AMP, ADP, ATP, Ap2A, and Cp4U are not). Among the products, a nucleoside monophosphate is always formed. The specificity of cleavage of methylated dinucleoside triphosphates and the molecular weight of dinucleoside triphosphatase indicate that this enzyme is different from the mRNA decapping enzyme previously characterized (A. Stevens, Mol. Cell. Biol. 8:2005-2010, 1988).
 ...
PMID:Isolation and characterization of a dinucleoside triphosphatase from Saccharomyces cerevisiae. 165 9

Botulinum C2 toxin, a binary toxin that ADP-ribosylates nonmuscle G-actin, was used as a selective tool to evaluate the role of actin-dependent cytoskeletal rearrangement in ligand-evoked lipid mediator generation. Human neutrophils (PMN) were preincubated with varying concentrations of the toxin for 30 min. Lipoxygenase products of arachidonic acid were measured by chromatographic techniques in the presence of exogenous arachidonic acid to probe PMN 5-lipoxygenase activity. Formation of platelet-activating factor (PAF) was assayed by the bioincorporation of [3H]acetate. Stimulation was performed with the soluble chemotactic ligands formyl-methionyl-leucyl-phenylalanine (FMLP) and PAF, as well as opsonized zymosan. PMN pretreatment with C2 toxin in the range between 200/400 and 800/1600 ng/ml C2I/II caused a dose-dependent suppression of the basal F-actin content and of stimulus-induced actin assembly. Phosphoinositide hydrolysis (measured as liberated inositol phosphates) and PAF generation in response to FMLP and exogenous PAF were markedly increased at these toxin doses. Minor C2 toxin concentrations (range, approximately 25/50 to 200/400 ng/ml C2I/II) were sufficient to amplify stimulus-induced formation of leukotriene B4 and its omega-oxidation products, nonenzymatic hydrolysis products of leukotriene A4, and 5-hydroxyeicosatetraenoic acid (5-HETE). With increasing toxin doses, leukotriene generation declined and 5-HETE became the predominant metabolite. In contrast to the soluble ligands, the zymosan-effected generation of PAF and leukotrienes was dose-dependently inhibited by C2 toxin concentrations of greater than 200/400 ng/ml, paralleled by a loss of motile and phagocytotic functions in these cells. We conclude that selective inhibition of actin assembly amplifies PAF and 5-lipoxygenase product formation in response to soluble chemoattractants with distinct dose dependences. The augmentation of PAF generation may be linked to amplified second messenger levels at higher doses of C2 toxin, whereas the sensitivity of the 5-lipoxygenase metabolism to low concentrations may indicate toxin effect on a small, functionally specified, actin pool. The present data support an important role of cytoskeletal rearrangement in temporal and/or spatial limitation of chemoattractant-evoked PMN activation.
Mol Pharmacol 1991 Oct
PMID:Inhibition of cytoskeletal rearrangement by botulinum C2 toxin amplifies ligand-evoked lipid mediator generation in human neutrophils. 165 92


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