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)

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.
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PMID:G-protein stimulation inhibits amiloride-sensitive Na/H exchange independently of cyclic AMP. 132 27

Prior studies indicate that cAMP-dependent protein kinase (PKA) and calcium calmodulin-dependent multifunctional protein kinase II (CaM-KII) inhibit Na(+)-H+ exchanger as assayed in octyl glucoside solubilized rabbit renal brush border membrane proteins reconstituted into artificial lipid vesicles. An anion exchange chromatography fraction of these proteins which elutes between 0.2 and 0.4 M NaCl (Fraction B), however, fails to demonstrate regulation of the transporter by PKA. The present studies examine regulation of the Na(+)-H+ exchanger by CaM-KII using Fraction B proteins. As compared to the initial total protein extract, Fraction B demonstrated increased Na(+)-H+ exchange activity. CaM-KII inhibited the Na(+)-H+ exchanger in Fraction B by 38.2 +/- 10.6% in an ATP and calmodulin-dependent manner. The results of the present studies suggest that CaM-KII-mediated inhibition of the Na(+)-H+ exchanger involves the phosphorylation of different polypeptides than those mediating the inhibition of this transporter by PKA.
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PMID:Regulation of the renal Na(+)-H+ exchanger by calcium calmodulin-dependent multifunctional protein kinase II. 132 33

The Na+-H+ exchanger from solubilized rabbit renal brush border membranes is inhibited by cAMP-dependent protein kinase (PKA) mediated protein phosphorylation. To characterize this inhibitory response and its sensitivity to limited proteolysis, the activity of the transporter was assayed after reconstitution of the proteins into artificial lipid vesicles. Limited trypsin digestion increased the basal rate of proton gradient-stimulated, amiloride-inhibitable sodium uptake in reconstituted proteoliposomes and blocked the inhibitory response to PKA-mediated protein phosphorylation. To determine if the inhibitory response to PKA-mediated protein phosphorylation could be restored to the trypsin-treated solubilized proteins, nontrypsinized solubilized brush border membrane proteins were separated by column chromatography. The addition of small molecular weight polypeptides, fractionated on Superose-12 FPLC (Ve = 0.7), to trypsinized solubilized brush border membrane proteins restored the inhibitory response to PKA-mediated protein phosphorylation. Similarly, the addition of the 0.1 M NaCl fraction from an anion exchange column, Mono Q-FPLC, also restored the inhibitory response to PKA. Both protein fractions contained a common 42-43 kDa protein which was preferentially phosphorylated by PKA. These results indicate that limited trypsin digestion dissociates the activity of the renal Na+-H+ exchanger from its regulation by PKA. It is suggested that trypsin cleaves an inhibitory component of the transporter and that this component is the site of PKA-mediated regulation. Phosphoprotein analysis of fractions that restored PKA regulation raises the possibility that a polypeptide of 42-43 kDa is involved in the inhibition of the renal Na+-H+ exchanger by PKA-mediated protein phosphorylation.
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PMID:Effect of limited trypsin digestion on the renal Na+-H+ exchanger and its regulation by cAMP-dependent protein kinase. 255 24

The effects of isoquinolinesulfonamides, which inhibit protein kinase, on fluid accumulations induced by heat-stable enterotoxin of enterotoxigenic Escherichia coli (STh), 8-bromo-cGMP and 8-bromo-cAMP in suckling mice were studied. Both N-[2-(methylamino)ethyl]-5-isoquinolinesulfonamide (H-8) and N-(2-aminoethyl)-5-isoquinolinesulfonamide (H-9) inhibited the fluid accumulation induced by STh. Fluid accumulation induced by four mouse units of STh (four-fold the minimum effective dose, 10 ng) was completely inhibited by 0.4 mumol of H-8 or H-9. H-8 and H-9 also inhibited fluid accumulation induced by 8-bromo-cGMP. On the other hand, H-8 and H-9 only partially inhibited fluid accumulation in suckling mice induced by 8-bromo-cAMP, probably because their affinities to cAMP-dependent protein kinase were lower than their affinities to cGMP-dependent protein kinase. From these results, it is concluded that the activation of cGMP-dependent protein kinase by increase in cGMP by ST or by 8-bromo-cGMP, and very probably the activation of cAMP-dependent protein kinase by increase in cAMP by cholera enterotoxin and heat-labile enterotoxin of enterotoxigenic E. coli and by 8-bromo-cAMP are necessary steps in signal transduction following increases in concentrations of cGMP and cAMP in intestinal brush border cells.
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PMID:Inhibition by the protein kinase inhibitors, isoquinolinesulfonamides, of fluid accumulation induced by Escherichia coli heat-stable enterotoxin, 8-bromo-cGMP and 8-bromo-cAMP in suckling mice. 256 Jan 8

Requirements for the activation of Cl- conductance have been investigated in pig jejunal brush border vesicles. The stability of ATP as a substrate for protein kinase activity, the stability of the phosphoprotein product of protein kinase action, and the choice of buffer system used for vesicle preparation were studied as variables which affected the outcome of in vitro activation attempts. Arsenate was selected as the most effective agent in protecting ATP from hydrolysis by the phosphatase activity in this vesicle system. Brush border vesicle protein appeared to prevent the accumulation of phosphoprotein in a cAMP-dependent protein kinase reaction, and vesicle protein only had phosphate acceptor activity when KF was added as a presumptive inhibitor of phosphoprotein phosphatase. A Cl- conductance response to a potassium gradient and valinomycin was present in vesicles prepared in buffers containing tetramethylammonium. Cl- conductance activity was not increased in this system by the addition of ATP, dibutyryl cyclic AMP, and cyclic AMP-dependent protein kinase. There was no Cl conductance response to a potassium gradient in vesicles buffered with imidazolium-acetate. Incorporation of ATP, AsO4(3-), and F- into these nonconductive vesicles by homogenization, followed by addition of dibutyryl cAMP, produced substantial conductance activity. Maximal activation of Cl- conductance was obtained with vesicles prepared in imidazolium-acetate buffering, using precautions to stabilize ATP and phosphoprotein prior to conductance measurements.
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PMID:Activation of chloride conductance in pig jejunal brush border vesicles. 271 42

Studies were performed to determine if the Na+-H+ exchanger, solubilized from renal brush border membranes from the rabbit and assayed in reconstituted artificial proteoliposomes, could be regulated by cAMP-dependent protein kinase. Octyl glucoside solubilized renal apical membrane proteins from the rabbit kidney were phosphorylated by incubation with ATP and highly purified catalytic subunit of cAMP-dependent kinase. 22Na+ uptake was determined subsequently after reconstitution of the proteins into proteoliposomes. cAMP-dependent protein kinase resulted in sustained protein phosphorylation and a concentration-dependent decrease in the amiloride-sensitive component of pH gradient-stimulated sodium uptake. The inhibitory effect of cAMP-dependent protein kinase demonstrated an absolute requirement for ATP and was blocked by the specific protein inhibitor of this kinase. cAMP-dependent protein kinase also inhibited 22Na+ uptake in the absence of a pH gradient (pHin 6.0, pHout 6.0) and the inhibitory effect was blocked by the specific inhibitor of the kinase. Solubilized membrane proteins exhibited little endogenous protein kinase or protein phosphatase activity. These studies indicate that Na+-H+ exchange activity of proteoliposomes reconstituted with proteins from renal brush border membranes is inhibited by phosphorylation of selected proteins by cAMP-dependent protein kinase. These findings also indicate that the regulatory components of the Na+-H+ exchanger remain active during the process of solubilization and reconstitution of renal apical membrane proteins.
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PMID:Reconstitution of cAMP-dependent protein kinase regulated renal Na+-H+ exchanger. 283 85

Photolabelling with 32P-8-azido-cAMP identified a major cAMP-binding protein (54 kDa) in isolated rabbit renal apical membranes, whose labelling was competitively inhibited by cAMP. Membrane associated cAMP-binding polypeptides were extensively purified by affinity chromatography on cAMP-Sepharose. The 54 kDa polypeptide represented 70-80% of the total protein eluted with cAMP. This protein was rapidly phosphorylated by the catalytic subunit of cAMP-dependent protein kinase, with a shift in its apparent mobility on SDS-PAGE to Mr 56/58,000. The phosphopeptide maps of autophosphorylated rat skeletal muscle RII and rabbit kidney 56/58 kDa proteins were essentially identical. Western immuno-blot analysis, using antibodies generated against purified rat RI and RII, indicated preferential cross-reactivity of rabbit kidney 54 kDa protein with anti-RII antibodies. The data demonstrates the specific association of the regulatory subunit of type II cAMP dependent protein kinase with rabbit renal brush border membranes.
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PMID:Type II cAMP-dependent protein kinase is associated with the rabbit kidney brush border membranes. 285 61

cAMP-dependent protein kinase, Ca+2- and phospholipid-dependent protein kinase, and protein kinase inhibitor activity were examined in renal homogenates and 20,000 X g supernatant fractions of normal and Hyp mice. In both genotypes, 70% of total renal cAMP-dependent protein kinase activity was recovered in the soluble fraction in which the activity ratio (without cAMP to with cAMP) of the enzyme was 0.35. The requirement for cAMP was not different for protein kinase of normal and mutant littermates, with an apparent Km for cAMP of 0.05 microM in both genotypes. Furthermore, vitamin D and calcium deficiencies did not significantly affect cAMP-dependent protein kinase activity in normal and Hyp mouse kidney. The concentration of the heat-stable protein kinase inhibitor protein in the 20,000 X g supernatant fraction was identical in normal and Hyp kidney. Whereas protein kinase inhibitor levels were increased 1.8-fold by vitamin D and calcium deficiencies in normal mice (P less than 0.001), no such increase was detectable in Hyp mice. Ca+2- and phospholipid-dependent-protein kinase (protein kinase C) activity in the 20,000 X g supernatant fraction comprised 50% of the total activity of kidney homogenates of both normal and mutant mice. The initial rate of protein kinase C was increased 1.5-fold in kidney supernatants of Hyp mice (P less than 0.001). In contrast, protein kinase C was not significantly different from normal in supernatant fractions of heart, spleen, and liver prepared from Hyp mice. The present demonstration of abnormally high renal protein kinase C activity in Hyp mice may serve to explain the relationship between the previously reported renal defects in brush border membrane phosphate transport and vitamin D metabolism in the mutant strain and elucidate the nature of the primary defect in the Hyp mouse.
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PMID:Protein kinase activity and protein kinase inhibitor in mouse kidney: effect of the X-linked Hyp mutation and vitamin D status. 299 97

We have previously demonstrated cAMP-dependent 32P phosphorylation and dephosphorylation of a 62,000 relative molecular weight (Mr) protein in autoradiograms of sodium dodecyl sulfate polyacrylamide gels originating from canine renal brush border membranes. In the current studies 32P phosphorylation of the 62,000 Mr protein that was independent of cAMP was noted in the presence of Zn2+. Under these conditions, cAMP inhibited the 32P phosphorylation of this protein. Concentration-dependent photoaffinity labeling of a band with Mr 60,000 in autoradiograms of gels resulted from incubation of membranes with cyclic 8-azidoadenosine-3',5'-monophosphate (8-N3-[32P]cAMP) followed by exposure to light. In the presence of Zn2+ and ATP, an apparent shift in the Mr of a portion of the photoaffinity-labeled band to 62,000 was seen. The 62,000 Mr phosphoprotein in detergent-solubilized supernatants of brush border membranes was immunoprecipitated with antibodies directed against the regulatory subunit of type II cAMP-dependent protein kinase. Our observations strongly suggest that the 62,000 Mr protein is the regulatory subunit.
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PMID:Phosphorylation of type II cAMP-dependent protein kinase in renal brush border membranes. 300 77

cAMP modulates estrogen, hCG, and lactate syntheses by human placenta, cAMP presumably exerts its major intracellular effect by binding to cAMP-dependent protein kinase (cAMP-PK), which, in turn, phosphorylates regulatory proteins within the target cell. cAMP binding and cAMP-PK have not been previously identified in placenta. [3H]cAMP binding to crude cytosol fractions of term placenta was rapid, saturable, and reversible. Scatchard analyses of saturation experiments of [3H]cAMP binding to placental cytosol were linear (Kd = 1.13 +/- 0.11 x 10(-8) M; n = 5). The binding capacity was 1.27 +/- 0.18 pmol/mg protein. Competition for the [3H]cAMP-binding site followed the potency order cAMP much greater than cGMP much greater than (Bu)2cAMP, analogous to cAMP binding to cAMP-PK in other tissues. ADP, ATP, and adenosine did not compete for the [3H]cAMP-binding site. cAMP significantly enhanced phosphorylation of histone protein by placental cytosol (activity ratio, 0.57 +/- 0.04; P less than 0.01). Two peaks of [3H]cAMP binding and coincident cAMP-PK activity were identified by DEAE-cellulose column chromatography of placental cytosol corresponding to classical type I and type II cAMP-PK. While the majority of the cAMP-PK was found in placental cytosol, cAMP-PK was also demonstrated in crude microsomal and microvillous brush border membranes of human placenta after solubilization with Triton X-100 (P less than 0.05). Regulation of placental function by catecholamines and other hormones known to mediate cAMP levels may be accomplished through the phosphorylation of cellular proteins by cAMP-dependent protein kinases.
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PMID:Adenosine 3',5'-monophosphate (cAMP)-binding protein and cAMP-dependent protein kinase in human placenta. 630 Jan 72


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