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

G-proteins are heterotrimeric proteins involved in many transmembrane signaling events. Both the renal basolateral membrane and the renal brush border membrane contain large quantities of these proteins. G-proteins appear related to hormonal signaling in the basolateral membrane and presumably affect ion gating in the brush border. We investigated the influence of G-proteins on the amiloride-sensitive Na/H exchanger, the activity of which is regulated at least in part by cAMP-dependent protein kinase, by measuring the amiloride-sensitive component of [22Na+] uptake in rat renal brush border membrane vesicles (BBMV) in the presence of a pH gradient. Incubation of vesicles with AlF4- (10 microM Al3+, 10 mM F-) resulted in significant inhibition of amiloride-sensitive [22Na+] uptake at both 20 seconds and 5 minutes of incubation. Incorporation of GTP gamma S into BBMV by transient hypotonic lysis also resulted in significantly reduced amiloride-sensitive [22Na+] uptake compared to controls at both time points. This inhibition could be reversed by GDP beta S. Similar lysis in the presence of 10 microM GDP beta S alone had no significant effect. When Na(+)-dependent [14C]-D-glucose uptake into BBMV was studied no significant effect of these G-protein modulating agents was observed. Adenylate cyclase activity could not be stimulated in these BBMV preparations using standard techniques. Furthermore, cAMP-dependent protein kinase activity, strongly stimulated in these BBMV by exogenously added cAMP, was not stimulated by 10 microM GTP gamma S alone. These findings suggest that the amiloride-sensitive Na/H exchanger can be regulated by G-proteins independently of adenylate cyclase and cAMP-dependent protein kinase.
 ...
PMID:G-protein stimulation inhibits amiloride-sensitive Na/H exchange independently of cyclic AMP. 132 27

Beta-Adrenoceptor agonists activate a time- and voltage-independent Cl- conductance in mammalian cardiac myocytes. To characterize the cellular signaling pathways underlying its regulation, wide-tipped pipettes fitted with a pipette perfusion device were used to record whole-cell current and to introduce nucleotides to the interior of guinea pig ventricular myocytes. Replacement of pipette GTP with GDP beta S prevented activation of the Cl- conductance by Iso, suggesting a requirement for G protein turnover. With GTP in the pipette, the effect of Iso could be abolished by the beta-adrenoceptor antagonist propranolol, and mimicked by histamine or forskolin. These actions of Iso and forskolin are mediated exclusively via cAMP-dependent protein kinase (PKA), because (a) maximal activation of the Cl- conductance by forskolin or pipette cAMP occluded the effect of Iso, and (b) switching to pipette solution containing a synthetic peptide inhibitor (PKI) of PKA completely abolished the Cl- conductance activated by Iso and prevented the action of forskolin, but had no further effect. These results argue against basal activation of the Cl- conductance, and make it extremely unlikely that the stimulatory G protein, Gs, has any direct, phosphorylation-independent influence. The muscarinic receptor agonists acetylcholine (ACh) and carbachol diminished, in a reversible manner, Cl- conductance activated by Iso or forskolin, but not that elicited by cAMP. The muscarinic inhibition was abolished by replacing pipette GTP with GDP beta S, or by preincubating cells with pertussis toxin (PTX), and was therefore mediated by an inhibitory G protein, presumably Gi, influencing adenylyl cyclase activity. Nonhydrolyzable GTP analogues (GTP gamma S or GppNHp) applied via the pipette did not themselves activate Cl- conductance, but rendered Cl- current activation by brief exposures to Iso or histamine, but not to forskolin, irreversible. The Cl- conductance persistently activated by Iso was insensitive to propranolol or ACh, but could still be abolished by pipette application of PKI. The data indicate that stimulation of beta-adrenergic or histaminergic receptors in the presence of nonhydrolyzable GTP analogues causes persistent activation of Gs and uncouples it from the receptors. We conclude that autonomic regulation of cardiac Cl- conductance reflects accurately the underlying modulation of adenylyl cyclase activity and, hence, that this system is a suitable mammalian model for in situ studies of the interactions between adenylyl cyclase, Gs, Gi, and forskolin.
 ...
PMID:Role of GTP-binding proteins in the regulation of mammalian cardiac chloride conductance. 137 58

In guinea pig ventricular myocytes, the effect of histamine on the slow Ca2+ current (ICa) was studied and the following results were obtained: (1) Superfusion of cells with histamine resulted in a dose-dependent enhancement of the amplitude of ICa. The threshold concentration of histamine was 10(-8) M, half maximal increase occurred at 3 X 10(-7) M and maximal enhancement (about 3-4-fold) at 5 X 10(-6) M. (2) The histamine effect was greatly reduced by the H2 antagonist cimetidine (10(-5) M) but only slightly by the H1 antagonist diphenhydramine (10(-5) M). (3) Effects of isoprenaline (ISP) and histamine at maximal effective concentrations on ICa were not additive, suggesting that both agents use the same intracellular pathway. Intracellular infusion of a blocker of the cAMP-dependent protein kinase, Rp-cAMPS (10(-4) M), prevented the histamine effect. (4) The involvement of GTP-dependent transducer proteins was studied by cell dialysis with several GTP derivatives. Intracellular application of the stable GDP-analogue, GDP-beta-S, reduced the histamine effect on ICa, whereas the stable GTP analogue, GTP-gamma-S, mimicked the histamine effect.
 ...
PMID:On the mechanism of histamine induced enhancement of the cardiac Ca2+ current. 244 49

We have separated multiple small Mr GTP-binding proteins (G proteins) from bovine brain membranes by several column chromatographies and purified to near homogeneity four of them, including a novel Mr 24,000 G protein (smg p25A), a novel Mr 22,000 G protein (smg p21), the rho protein (rho p20), and the c-Ki-ras protein (c-Ki-ras p21). Among these small Mr G proteins, only smg p21 is phosphorylated stoichiometrically by cAMP-dependent protein kinase (protein kinase A), and c-Ki-ras p21 is phosphorylated to a small extent by protein kinase A in a cell-free system. None of smg p25A, rho p20, and other partially purified small Mr G proteins is phosphorylated by protein kinase A. Neither smg p21 nor other small Mr G proteins are phosphorylated by protein kinase C. About 1 mol of phosphate is maximally incorporated into 1 mol of smg p21 by protein kinase A. Only serine residue(s) are phosphorylated. The guanosine 5'-3-O-(thio) triphosphate (GTP gamma S)-bound and GDP-bound forms of smg p21 are phosphorylated with the same reaction velocity. The phosphorylation of smg p21 affects neither its GTP gamma S-binding nor GTPase activity. smg p21 is found in human platelets, and this human platelet smg p21 is also phosphorylated by protein kinase A at the same site(s) as bovine brain smg p21 in a cell-free system. When intact human platelets are stimulated by prostaglandin E1 known to elevate the cAMP level, four proteins with apparent Mr values of 240,000, 50,000, 24,000, and 22,000 are phosphorylated. These four proteins are also phosphorylated by the action of dibutyryl cAMP but not by the action of thrombin, Ca2+ ionophore A23187, or 12-O-tetradecanoylphorbol-13-acetate. Among the four proteins, the Mr 22,000 protein is identified as smg p21. The site(s) of phosphorylation of smg p21 by protein kinase A in a cell-free system are identical to that phosphorylated in response to prostaglandin E1 in intact platelets. These results indicate that among many small Mr G proteins, smg p21 is selectively phosphorylated by protein kinase A and that this G protein is also phosphorylated by this protein kinase in response to prostaglandin E1 in intact human platelets.
 ...
PMID:Phosphorylation of smg p21, a ras p21-like GTP-binding protein, by cyclic AMP-dependent protein kinase in a cell-free system and in response to prostaglandin E1 in intact human platelets. 250 24

We have investigated the possible role of a cAMP-mediated protein-phosphorylation event(s) as the key regulatory mechanism in beta-adrenoreceptor-stimulated activation of mannosylphosphodolichol (Man-P-Dol) synthase (GDP-mannose:dolichyl-phosphate O-beta-D-mannosyltransferase, EC 2.4.1.83) in rat parotid acinar cells. Microsomal membranes isolated from these cells pretreated with 10 microM isoproterenol for 60 min showed approximately 40-80% enhanced Man-P-Dol synthase activity compared to the untreated controls. This change in enzyme activity was not associated with a significant alteration in apparent Km for GDP-mannose, but the Vmax was enhanced 2-fold. When microsomal membranes isolated from control cells were phosphorylated in vitro by a cAMP-dependent protein kinase, an increase in Man-P-Dol synthase activity, similar to that with membranes from isoproterenol-treated cells, was observed (i.e., a moderate change in Km for GDP-mannose but a 2-fold higher Vmax). Furthermore, treatment of in vitro phosphorylated microsomal membranes by alkaline phosphatase led to a substantial reduction in Man-P-Dol synthase activity. Increased Man-P-Dol synthesis (approximately 30-40%) was also observed in bovine brain and hen oviduct microsomal membranes after in vitro protein phosphorylation. In aggregate, these results strongly suggest that agents that increase cAMP in cells may modulate protein N-glycosylation in those cells by activating this key glycosyltransferase of the dolichol cascade by a cAMP-dependent protein kinase-mediated protein phosphorylation/dephosphorylation cycle.
 ...
PMID:cAMP-mediated protein phosphorylation of microsomal membranes increases mannosylphosphodolichol synthase activity. 281 74

The GDP-bound alpha subunit of transducin, but not the guanosine 5'-[gamma-thio]triphosphate-bound one, undergoes phosphorylation on tyrosine residues by the insulin receptor kinase and on serine residues by protein kinase C. Holotransducin is poorly phosphorylated by the insulin receptor kinase and is not phosphorylated by protein kinase C. Neither holotransducin nor any of its subunits were phosphorylated by the cAMP-dependent protein kinase. That a given subunit of transducin undergoes multisite phosphorylation depending on the type of nucleotide bound to it or the nature of the kinase suggests that hormone-dependent phosphorylation could provide a versatile mode for regulation of guanine nucleotide-binding protein (G protein) function. In particular, the findings that certain G proteins serve as substrates for both the insulin receptor kinase and protein kinase C implicate G proteins in playing a key role in mediating the action of insulin and ligands that act to activate protein kinase C.
 ...
PMID:Multisite phosphorylation of the alpha subunit of transducin by the insulin receptor kinase and protein kinase C. 309 81

Forskolin (40 microM) stimulated adenylate cyclase activities of bovine thyroid plasma membranes without the addition of guanine nucleotides. GDP had little effect on the forskolin-stimulated adenylate cyclase activity while Gpp[NH]p (0.1-1.0 microM) decreased it. In the presence of TSH (10 mU/0.11), Gpp[NH]p no longer caused inhibition. Forskolin did not affect phosphodiesterase activities of thyroid homogenates. Forskolin (10 microM) rapidly increased cAMP levels in bovine thyroid slices both in the absence and presence of a phosphodiesterase inhibitor. The effect of TSH (50 mU/ml) on cAMP levels was additive or greater than additive to that of forskolin. An initial 2-h incubation of slices with forskolin did not decrease their subsequent cAMP responses to either forskolin and/or TSH while similar treatment of slices with TSH induced desensitization of the cAMP response to TSH, but not to forskolin. Forskolin (10 microM) as well as TSH (50 mU/ml) activated cAMP-dependent protein kinase of slices in the absence of a phosphodiesterase inhibitor. Although forskolin activated the adenylate cyclase cAMP system, it did not stimulate iodide organification or glucose oxidation, effects which have been attributed to cAMP. In fact, forskolin inhibited these parameters and 32P incorporation into phospholipids as well as their stimulation by TSH. These results indicate that an increase in cAMP levels and cAMP-dependent protein kinase activity in thyroid slices may not necessarily reproduce the effects of TSH on the thyroid.
 ...
PMID:Effects of forskolin on adenylate cyclase, cyclic AMP, protein kinase and intermediary metabolism of the thyroid gland. 629 78

Purified casein kinase G was found able to catalyse the synthesis of [gamma-32P]ATP in the presence of ADP, phosphocasein (previously 32P-labeled by the forward kinase reaction) and magnesium. Apparent Km values of approx. 0.5 mM for phosphocasein and 7.5 mM for ADP were calculated, these values indicating low affinities for the substrates as compared to those exhibited for casein and ATP in the forward reaction. The reverse casein kinase G activity appeared to prefer ADP and GDP as phosphate acceptors. Whereas the casein kinase G reverse reaction could be supported by casein, phosvitin and histone previously phosphorylated by the enzyme, the same proteins could not serve as a phosphate source when previously phosphorylated by the cAMP-dependent protein kinase. Forward and reverse casein kinase G reactions exhibited different optimal pH values (8.5 and 7.2, respectively) and a different sensitivity to Mg2+. Spermine, which activated the kinase activity, blocked the reverse reaction at millimolar concentrations. Although the biological significance of the casein kinase G reverse activity remains to be assessed in intact cell, the process may be useful as a tool in the characterization of phosphorylatable sites in phosphoproteins.
 ...
PMID:Reversibility of the phosphate transfer between ATP and phosphoproteins catalysed by a cyclic nucleotide independent (G type) casein kinase. 657 5

(1) Pyruvate kinase type M2 from rat lung has been purified 840-fold with an overall yield of 20%. The enzyme gave a single band upon SDS-electrophoresis and isoelectrofocusing and had a specific activity of 1340 U/mg protein. The homotetramer of Mr = 224000 and an isoelectric point of pH 5.8 had an amino acid composition closely resembling that of other pyruvate kinase isoenzymes type M2, except that of the chicken liver. The enzyme was crystallized. (2) The enzyme has its pH optimum at pH 6.5. The K0.5 value for phosphoenolpyruvate is 0.26 mM (nH = 1.81) which decreases in the presence of 0.2 mM fructose 1,6-bisphosphate to 0.056 mM (nH = 1.06). 1 microM fructose 1,6-bisphosphate activates the enzyme at 0.1 mM phosphoenolpyruvate half-maximally. The Km value for ADP at 1 mM phosphoenolpyruvate is 0.4 mM. The Km value for other nucleoside diphosphates increases in the order ADP less than GDP less than IDP less than UDP. (3) No evidence for an interconversion of pyruvate kinase type M2 from rat or chicken lung was found. The enzyme was neither a substrate for the cAMP-dependent protein kinase from rabbit muscle nor for the cAMP-independent protein kinase from chicken liver. Since pyruvate kinase type M2 from chicken liver is inactivated by phosphorylation catalyzed by a cAMP-independent protein kinase (Eigenbrodt, E., Abdel-Fattah Mostafa, M. and Schoner, W. (1977) Hoppe-Seyler's Z. Physiol. Chem. 358, 1047-1055) we suggest that the interconvertible form of pyruvate kinase type M2 may represent a separate form of the pyruvate kinase type M2 family.
 ...
PMID:Purification and properties of pyruvate kinase type M2 from rat lung. 711 73

ATP produced whole-cell potassium currents in cultured endothelial cells of the bovine brain cortical arteries. P2 purinoceptor agonists evoked similar currents with the order of their potency: 2-methylthio ATP > ATP >> alpha, beta-methylene ATP > or = UTP > or = ADP >> AMP. ATP-evoked currents were inhibited by GDP beta S, but not by pertussis toxin (PTX). Furthermore, a phospholipase C (PLC) inhibitor, protein kinase C inhibitor, or cAMP-dependent protein kinase inhibitor had no effect on the currents. In addition to these effects, ATP enhanced intracellular free Ca2+ concentration ([Ca2+]i) in the presence and absence of extracellular Ca2+, and this [Ca2+]i increase was not inhibited by a PLC inhibitor. These results, thus, provide an indication that ATP activates the potassium channel and enhances [Ca2+]i via a P2Y purinoceptor linked to a PTX-insensitive G-protein, which is not involved in a PLC-mediated signaling pathway.
 ...
PMID:ATP activates the potassium channel and enhances cytosolic Ca2+ release via a P2Y purinoceptor linked to pertussis toxin-insensitive G-protein in brain artery endothelial cells. 748 26


1 2 3 Next >>