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)

The heat shock response is an inducible protective system of all living cells. It simultaneously induces both heat shock proteins and an increased capacity for the cell to withstand potentially lethal temperatures (an increased thermotolerance). This has lead to the suspicion that these two phenomena must be inexorably linked. However, analysis of heat shock protein function in Saccharomyces cerevisiae by molecular genetic techniques has revealed only a minority of the heat shock proteins of this organism having appreciable influences on thermotolerance. Instead, physiological perturbations and the accumulation of trehalose with heat stress may be more important in the development of thermotolerance during a preconditioning heat shock. Vegetative S. cerevisiae also acquires thermotolerance through osmotic dehydration, through treatment with certain chemical agents and when, due to nutrient limitation, it arrests growth in the G1 phase of the cell cycle. There is evidence for the activities of the cAMP-dependent protein kinase and plasma membrane ATPase being very important in thermotolerance determination. Also, intracellular water activity and trehalose probably exert a strong influence over thermotolerance through their effects on stabilisation of membranes and intracellular assemblies. Future investigations should address the unresolved issue of whether the different routes to thermotolerance induction cause a common change to the physical state of the intracellular environment, a change that may result in an increased stabilisation of cellular structures through more stable hydrogen bonding and hydrophobic interactions.
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PMID:Molecular events associated with acquisition of heat tolerance by the yeast Saccharomyces cerevisiae. 839 11

A functional approach was utilized to isolate protein effectors from cAMP-stimulated rabbit gastric microsomes capable of stimulating H(+)-K(+)-ATPase activity. These studies have resulted in isolation of a cAMP-dependent protein kinase product from rabbit gastric microsomes which is capable of stimulating the proton pump of the parietal cell, H(+)-K(+)-ATPase, in inhibited gastric microsomes. This protein is membrane-bound and may be extracted from gastric microsomes only in the phosphorylated state. This phosphoprotein has at least 20 phosphorylation sites and produces enhancement of H(+)-K(+)-ATPase activity which equals that induced by the K+ ionophore, valinomycin. It would appear, therefore, that cAMP-mediated acid secretion involves phosphorylation of a membrane-bound cAMP-dependent protein kinase substrate in close proximity to the proton pump which produces K+ conductance and thereby controls the rate of acid secretion. The degree of phosphorylation of this protein is probably controlled by the activities of cAMP-dependent protein kinase and phosphoprotein phosphatase.
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PMID:Regulation of gastric H(+)-K(+)-ATPase by cAMP-dependent protein kinase. 841 3

The cAMP-dependent protein kinase is a bifunctional enzyme, catalyzing the phosphorylation of the serine and threonine residues in peptides and proteins (kinase activity) as well as the phosphorylation of water (ATPase activity). We have found that several peptides, which serve as inhibitors of the kinase reaction, will either maintain or enhance the ATPase reaction catalyzed by the enzyme. Positively charged dipeptides (e.g. Arg-Arg), as well as small guanidino-containing compounds (e.g. guanethidine) block protein kinase activity yet enhance ATPase activity up to 3.5-fold over that exhibited by the enzyme in the absence of these compounds. In contrast, several nonphosphorylatable peptides, whose primary sequences are based on that of a known substrate (i.e. Leu-Arg-Arg-Ala-Ser-Leu-Gly), such as Leu-Arg-Arg-Ala-Ala-Leu-Gly, Leu-Arg-Arg-Ala-Phe-Leu-Gly, and Leu-Arg-Arg-Ala-Tyr-Leu-Gly, have little or no effect on the rate of the kinase-catalyzed hydrolysis of ATP. An exception to the latter observation is Leu-Arg-Arg-Ala-Cys-Leu-Gly, a cysteine-containing peptide that promotes the protein kinase-catalyzed ATPase reaction by 2.2-fold. We have also found that peptides that possess relatively large amino acid side chain moieties immediately following the arginine dyad (i.e. such as Phe, Tyr, Cys, or Asn at Xaa in Leu-Arg-Arg-Xaa-Ala-Leu-Gly) sharply reduce the rate of enzyme-catalyzed ATP hydrolysis. This suggests that in the presence of peptides containing an -Arg-Arg-Ala- sequence, the enzyme-bound gamma-phosphate of ATP is relatively accessible to water. In contrast, when the latter alanine moiety is replaced by a larger residue, access by water to ATP appears to be hindered. These results indicate that certain structural features associated with the substrate or substrate analog have a profound influence on the manner by which these species interact with the protein kinase. Furthermore, the work described herein demonstrates that it is possible to block the physiologically important kinase reaction and simultaneously promote the energetically wasteful ATPase reaction.
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PMID:ATPase-promoting dead end inhibitors of the cAMP-dependent protein kinase. 850 66

Maintenance of cytoplasmic pH (pHi) within a narrow physiological range is crucial to normal cellular function. This is of particular relevance to phagocytic cells within the acidic inflammatory microenvironment where the pHi tends to be acid loaded. We have previously reported that a vacuolar-type H(+)-ATPase (V-ATPase) situated in the plasma membrane of macrophages and poised to extrude protons from the cytoplasmic to the extracellular space is an important pHi regulatory mechanism within the inflammatory milieu. Since this microenvironment is frequently characterized by the influx of cells known to release inflammatory cytokines, we performed studies to examine the effect of one such mediator molecule, interleukin-1 (IL-1), on pHi regulation in peritoneal macrophages. IL-1 caused a time- and dose-dependent increase in macrophage pHi recovery from an acute acid load. This effect was specific to IL-1 and was due to enhanced plasmalemmal V-ATPase activity. The increased V-ATPase activity by IL-1 occurred following a lag period of several hours and required de novo protein and mRNA synthesis. However, Northern blot analysis revealed that IL-1 did not exert its effect via alterations in the levels of mRNA transcripts for the A or B subunits of the V-ATPase complex. Finally, stimulation of both cAMP-dependent protein kinase and protein kinase C was required for the stimulatory effect of IL-1 on V-ATPase activity. Thus, cytokines present within the inflammatory milieu are able to modulate pHi regulatory mechanisms. These data may represent a novel mechanism whereby cytokines may improve cellular function at inflammatory sites.
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PMID:Interleukin-1 increases vacuolar-type H+-ATPase activity in murine peritoneal macrophages. 856 51

Regulation of calcium transport by sarcoplasmic reticulum provides increased cardiac contractility in response to beta-adrenergic stimulation. This is due to phosphorylation of phospholamban by cAMP-dependent protein kinase or by calcium/calmodulin-dependent protein kinase, which activates the calcium pump (Ca2+-ATPase). Recently, direct phosphorylation of Ca2+-ATPase by calcium/calmodulin-dependent protein kinase has been proposed to provide additional regulation. To investigate these effects in detail, we have purified Ca2+-ATPase from cardiac sarcoplasmic reticulum using affinity chromatography and reconstituted it with purified, recombinant phospholamban. The resulting proteoliposomes had high rates of calcium transport, which was tightly coupled to ATP hydrolysis (approximately 1.7 calcium ions transported per ATP molecule hydrolyzed). Co-reconstitution with phospholamban suppressed both calcium uptake and ATPase activities by approximately 50%, and this suppression was fully relieved by a phospholamban monoclonal antibody or by phosphorylation either with cAMP-dependent protein kinase or with calcium/calmodulin-dependent protein kinase. These effects were consistent with a change in the apparent calcium affinity of Ca2+-ATPase and not with a change in Vmax. Neither the purified, reconstituted cardiac Ca2+-ATPase nor the Ca2+-ATPase in longitudinal cardiac sarcoplasmic reticulum vesicles was a substrate for calcium/calmodulin-dependent protein kinase, and accordingly, we found no effect of calcium/calmodulin-dependent protein kinase phosphorylation on Vmax for calcium transport.
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PMID:Purified, reconstituted cardiac Ca2+-ATPase is regulated by phospholamban but not by direct phosphorylation with Ca2+/calmodulin-dependent protein kinase. 866 79

Ca2+ transport by cardiac sarcoplasmic reticulum is tightly coupled with the enzymatic activity of Ca2+-dependent ATPase, which forms and decomposes an intermediate phosphoenzyme. Heart sarcoplasmic reticulum Ca2+ pump is regulated by cAMP-dependent protein kinase (PKA) phospholamban phosphorylation, which results in a stimulation of the initial rates of Ca2+ transport and Ca2+ ATPase activity. In the present studies we found that acylphosphatase from heart muscle, used at concentrations within the physiological range, actively hydrolyzes the phosphoenzyme of cardiac sarcoplasmic reticulum Ca2+ pump, with an apparent Km on the order of 10(-7) M, suggesting an high affinity of the enzyme for this special substrate. In unphosphorylated vesicles acylphosphatase enhanced the rate of ATP hydrolysis and Ca2+ uptake with a concomitant significant decrease in apparent Km for Ca2+ and ATP. In vesicles whose phospholamban was PKA-phosphorylated, acylphosphatase also stimulated the rate of Ca2+ uptake and ATP hydrolysis but to a lesser extent, and the Km values for Ca2+ and ATP were not significantly different with respect to those found in the absence of acylphosphatase. These findings suggest that acylphosphatase, owing to its hydrolytic effect, accelerates the turnover of the phosphoenzyme intermediate with the consequence of an enhanced activity of Ca2+ pump. It is known that phosphorylation of phospholamban results in an increase of the rate at which the phosphoenzyme is decomposed. Thus, as discussed, a competition between phospholamban and acylphosphatase effect on the phosphoenzyme might be proposed to explain why the stimulation induced by this enzyme is less marked in PKA-phosphorylated than in unphosphorylated heart vesicles.
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PMID:Stimulation of cardiac sarcoplasmic reticulum calcium pump by acylphosphatase. Relationship to phospholamban phosphorylation. 870 78

The effects of cyclic AMP (cAMP) on intracellular Na+ concentration ([Na+]i), membrane depolarization and intracellular Ca2+ concentration ([Ca2+]i) and the involvement of cAMP in acetylcholine (ACh)-induced such cellular events and catecholamine (CA) release were studied in cultured bovine adrenal medullary chromaffin cells. 8-Bromo-cyclic AMP (8Br-cAMP) and forskolin caused a rise in [Na+]i, membrane depolarization and a rise in [Ca2+]i and potentiated these responses and CA release to ACh. The effects of 8Br-cAMP or forskolin on ACh-induced changes of but not on basal level of [Na+]i, membrane potential and [Ca2+]i were blocked by tetrodotoxin (TTX, 1 microM). In Na+ deprivated medium, forskolin failed to produce an increase in basal [Ca2+]i level and to potentiate ACh-induced rise. The similar results as in 8Br-cAMP and forskolin were obtained using ouabain, and 8Br-cAMP or foskolin produced no further effects in the presence of ouabain. Inhibitors of cAMP-dependent protein kinase not only blocked the effects of 8Br-cAMP and forskolin on membrane depolarization, [Ca2+]i rise and CA release, but also reduced these responses to ACh. From the similarity between the effects of cAMP and those of ouabain on the cellular events and the counteraction of the effects of cAMP by ouabain, it may be suggested that cAMP produces its effects on ion fluxes and CA release probably via an inhibition of Na+, K(+)-ATPase in intact chromaffin and cAMP may participate in the responses to ACh.
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PMID:Cyclic AMP enhances acetylcholine (ACh)-induced ion fluxes and catecholamine release by inhibiting Na+, K(+)-ATPase and participates in the responses to ACh in cultured bovine adrenal medullary chromaffin cells. 874 60

Nongenomic actions of thyroid hormone are by definition independent of nuclear receptors for the hormone and have been described at the plasma membrane, various cell organelles, the cytoskeleton, and in cytoplasm. The actions include alterations in solute transport (Ca2+, Na+, glucose), changes in activities of several kinases, including protein kinase C, cAMP-dependent protein kinase and pyruvate kinase M2 (PKM2), effects on efficiency of specific mRNA translation and mRNA t1/2, modulation of mitochondrial respiration, and regulation of actin polymerization (promotion of formation of F-actin). Iodothyronines also can regulate nongenomically the state of contractile elements in vascular smooth muscle cells (VSMC). The physiologic significance at the cellular level of certain of these actions has been demonstrated, for example, in the cases of myocardiocyte Na+ current, red cell Ca2+ content, and the control by hormone-induced alterations in actin solubility of cell surface activity of iodothyronine 5'-monodeiodinase activity and the intracellular distribution of protein disulfide isomerase activity. The physiologic significance of these actions at the organ or system level is less clear, but extranuclear effects of thyroid hormone on myocardial Na+ channel, sarcoplasmic reticulum Ca(2+)-ATPase activity, and contractile state of VSMC may each contribute to acute effects of thyroid hormone on cardiac output that have recently been described clinically. The molecular mechanisms for nongenomic actions are incompletely understood; relevant binding sites and signal transduction pathways have been described for hormone actions on plasma membrane Ca(2+)-ATPase activity, and PKM2 monomer is known to bind T3 and, as a result, prevent activation of the kinase via tetramer formation. Nongenomic actions of thyroid hormone may have different structure-activity relationships of iodothyronines from those effects that depend upon nuclear receptors; they may have different time courses and may invoke complex signal transduction pathways before the action is detected.
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PMID:Nongenomic actions of thyroid hormone. 893 79

A glycine-rich loop in the ATP-binding site is one of the most highly conserved sequence motifs in protein kinases. Each conserved glycine (Gly-50, Gly-52, and Gly-55) in the catalytic (C) subunit of cAMP-dependent protein kinase (cAPK) was replaced with Ser and/or Ala. Active mutant proteins were expressed in Escherichia coli, purified to apparent homogeneity, separated into phosphoisoforms, and characterized. Replacing Gly-55 had minimal effects on steady-state kinetic parameters, whereas replacement of either Gly-50 or Gly-52 had major effects on both Km and kcat values consistent with the prediction of the importance of the tip of the glycine-rich loop for catalysis. Substitution of Gly-50 caused a 5-8-fold reduction in Km (ATP), an 8-12-fold increase in Km (peptide), and a 3-5-fold drop in kcat. The Km (ATP) and Km (peptide) values of C(G52S) were increased 8- and 18-fold, respectively, and the kcat was decreased 6-fold. In contrast to catalytic efficiency, the ATPase rates of C(G50S) and C(G52S) were increased by more than an order of magnitude. The thermostability of each mutant was slightly increased. Unphosphorylated C(G52S) was characterized as well as several isoforms phosphorylated at a single site, Ser-338. All of these phosphorylation-defective mutants displayed a substantial decrease in both enzymatic activity and thermal stability that correlated with the missing phosphate at Thr-197. These results are correlated with the crystal structure, models of the respective mutant proteins, and conservation of the Glys within the protein kinase family.
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PMID:Role of the glycine triad in the ATP-binding site of cAMP-dependent protein kinase. 920 6

To characterize and localize a K+/H+ antiport mechanism in the renal medullary thick ascending limb (MTAL), membrane vesicles were isolated from a rat MTAL homogenate. K+/H+ antiport (in > out H+ gradient-stimulated 86Rb+ uptake) was abolished by barium and verapamil (apparent Ki of 55 microM) but unaffected by other K+ channel blockers such as quinidine and high amiloride concentrations. SCH 28080, a H+/K+-ATPase blocker, did not affect K+/H+ antiport. K+/H+ antiport activity was correlated positively with the enrichment factor of the membranes in the apical marker enzyme alkaline phosphatase (r = 0.875, p < 0.01) and negatively correlated with the enrichment factor in basolateral Na+/K+-ATPase (r = -0.665, p < 0.05). Moreover, a functional interaction occurred with Na+/H+ exchange (NHE) consistent with colocation of K+/H+ antiport and apical NHE-3, not basolateral NHE-1. K+/H+ antiport was shown by intracellular pH measurements to be inhibited by arginine vasopressin and 8-bromo-cAMP through cAMP-dependent protein kinase (protein kinase A) activation. These results demonstrate the presence of a K+/H+ antiport mechanism, which is inhibited by arginine vasopressin via protein kinase A, in the apical membrane of the MTAL.
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PMID:Apical location and inhibition by arginine vasopressin of K+/H+ antiport of the medullary thick ascending limb of rat kidney. 932 90


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