Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.11.27 (AMPK)
 6,299 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. We have purified the AMP-activated protein kinase 4800-fold from rat liver. The acetyl-CoA carboxylase kinase and 3-hydroxy-3-methylglutaryl-CoA(HMG-CoA) reductase kinase activities copurify through all six purification steps and are inactivated with similar kinetics by treatment with the reactive ATP analogue fluorosulphonylbenzoyladenosine. 2. The final preparation contains several polypeptides detectable by SDS/polyacrylamide gel electrophoresis, but only one of these, with an apparent molecular mass of 63 kDa, is labelled using [14C]fluorosulphonylbenzoyladenosine. This is also the only polypeptide in the preparation that becomes significantly labelled during incubation with [gamma 32P]ATP. This autophosphorylation reaction did not affect the AMP-stimulated kinase activity. 3. In the absence of AMP the purified kinase has apparent Km values for ATP and acetyl-CoA carboxylase of 86 microM and 1.9 microM respectively. AMP increases the Vmax 3-5-fold without a significant change in the Km for either protein or ATP substrates. 4. The response to AMP depends on the ATP concentration in the assay, but at a near-physiological ATP concentration the half-maximal effect of AMP occurs at 14 microM. Studies with a range of nucleoside monophosphates and diphosphates, and AMP analogues showed that the allosteric activation by AMP was very specific. ADP gave a small stimulation at low concentrations but was inhibitory at high concentrations. 5. These results show that the AMP-activated protein kinase is the major HMG-CoA reductase kinase detectable in rat liver under our assay conditions and that it is therefore likely to be identical to previously described HMG-CoA reductase kinase(s) which are activated by adenine nucleotides and phosphorylation. The AMP-binding and catalytic domains of the kinase are located on a 63-kDa polypeptide which is subject to autophosphorylation.
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PMID:Purification and characterization of the AMP-activated protein kinase. Copurification of acetyl-CoA carboxylase kinase and 3-hydroxy-3-methylglutaryl-CoA reductase kinase activities. 259 24

Several links relate mitochondrial metabolism and type 2 diabetes or chronic hyperglycaemia. Among them, ATP synthesis by oxidative phosphorylation and cellular energy metabolism (ATP/ADP ratio), redox status and reactive oxygen species (ROS) production, membrane potential and substrate transport across the mitochondrial membrane are involved at various steps of the very complex network of glucose metabolism. Recently, the following findings (1) mitochondrial ROS production is central in the signalling pathway of harmful effects of hyperglycaemia, (2) AMPK activation is a major regulator of both glucose and lipid metabolism connected with cellular energy status, (3) hyperglycaemia by inhibiting glucose-6-phosphate dehydrogenase (G6PDH) by a cAMP mechanism plays a crucial role in NADPH/NADP ratio and thus in the pro-oxidant/anti-oxidant cellular status, have deeply changed our view of diabetes and related complications. It has been reported that metformin has many different cellular effects according to the experimental models and/or conditions. However, recent important findings may explain its unique efficacy in the treatment of hyperglycaemia- or insulin-resistance related complications. Metformin is a mild inhibitor of respiratory chain complex 1; it activates AMPK in several models, apparently independently of changes in the AMP-to-ATP ratio; it activates G6PDH in a model of high-fat related insulin resistance; and it has antioxidant properties by a mechanism (s), which is (are) not completely elucidated as yet. Although it is clear that metformin has non-mitochondrial effects, since it affects erythrocyte metabolism, the mitochondrial effects of metformin are probably crucial in explaining the various properties of this drug.
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PMID:Mitochondrial metabolism and type-2 diabetes: a specific target of metformin. 1450 5

Skeletal muscle has evolved an impressive array of mechanisms for peripherally mediated control of ATP homeostasis. Some of these mechanisms are intracellular, and others are extracellular and include influences on the cross-bridge cycle itself and substrate supply. This paper introduces three distinctly different topics that nevertheless all have ATP defense in common. The role of ADP in fatigue is controversial but has recently been more clearly delineated so that an effect on alleviating force declines during extreme fatigue is plausible. AMP plays its role by activating the protein-kinase, AMPK, which is a key sensor of cellular energy stress. AMPK has different isoforms, is not uniformly distributed in the cell, and its activation is carefully controlled. It has multiple effects including improvements in substrate supply for the metabolic pathways producing ATP and inhibition of anabolic processes to further spare ATP. Red blood cells have the capacity to sense hypoxia and to release vasodilators where there is a locally increased demand for blood supply. The papers in this series emphasize the important positive roles of metabolites and sensors of fatigue in the balance between ATP supply and demand.
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PMID:Protecting muscle ATP: positive roles for peripheral defense mechanisms-introduction. 1470 62

Thiazolidinediones have been shown to activate AMP-activated protein kinase activity in cultured cells. Whether they have a similar effect in vivo and if so whether it is physiologically relevant is not known. To assess these questions, we examined the effects of pioglitazone, administered orally to intact rats, on AMPK phosphorylation (AMPK-P) (a measure of its activation) and acetyl CoA carboxylase (ACC) activity and malonyl CoA concentration in rat liver and adipose tissue. In the first study, measurements were made in the Dahl-salt-sensitive rat (Dahl-S), a strain of Sprague-Dawley rat with endogenous hypertriglyceridemia and high levels of malonyl CoA that are restored to control values by pioglitazone. Treatment with pioglitazone (20mg/kg bw/day for 3 weeks) did not significantly increase either P-AMPK or P-ACC (which varies inversely with ACC activity) in control rats. However, in the Dahl-S rats values for AMPK-P and ACC-P were 50% lower than in control rats and were doubled by pioglitazone treatment. In a second study, the effects of two weeks treatment with pioglitazone (3mg/kg bw/day administered orally) were evaluated in Wistar rats. Under basal conditions (no manipulation of the animals), pioglitazone increased AMPK phosphorylation by twofold and decreased ACC activity and the concentration of malonyl CoA by 50% in liver. Following a euglycemic-hyperinsulinemic clamp (6h), 50% decreases in AMPK and ACC phosphorylation (indicating an increase in its activity) and comparable increases in malonyl CoA concentration were observed in liver and adipose tissue. In both tissues, pre-treatment with pioglitazone prevented these changes. Where studied (in Wistar rats under basal conditions) treatment with pioglitazone decreased the concentration of ATP by 1/3 and increased the concentration of ADP and AMP in liver. The results indicate that treatment with pioglitazone can increase AMPK activity in rat liver and adipose tissue in a variety of circumstances. They also suggest that this activation of AMPK may be mediated by a change in cellular energy state. Whether these effects of pioglitazone contribute to its insulin-sensitizing and other actions in vivo remains to be determined.
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PMID:Pioglitazone treatment activates AMP-activated protein kinase in rat liver and adipose tissue in vivo. 1473 47

Mitochondrial DNA (mtDNA) deletions occur sporadically in zygotic and somatic tissues and reach their highest concentration in substantia nigra. Previously, we noted the increase of the adenosine monophosphate (AMP)-activated protein kinase (AMPK) transcript by microarray in multiple cells and tissues bearing deletions. In this work, we demonstrate that the induction of AMPK transcript is dependent on deletions by quantitative polymerase chain reaction, and also demonstrate a deficiency in adenosine triphosphate (ATP) synthesis in the same cells. Consistent with AMPK induction, its known targets SREBF1 (sterol regulatory element binding protein-1) and ATG12 were inhibited and induced, respectively. AMPK induction is known to decrease secretory processes in some cells, and the secretion of both osteoprotegerin (OPG) and fibronectin (FN) proteins to the extracellular space was significantly deficient. Deletions caused a defect in the adenosine diphosphate (ADP)-ribosylation factor-like 2 (ARL2) transcript, which is known to be important in secretion and interacts with protein phosphatase 2A (PP2A) and thus AMPK. The deletion-dependent dysfunctions occurred even in cells bearing less than 30% deletions, suggesting that the concept of a high biological 'threshold' for deletions should be further revised downward. The defects in ATP synthesis, induction of the AMPK and SREBF1 transcripts, and decreased expression of ARL2 and secretion of OPG and FN were recapitulated by low doses of rotenone, demonstrating that they were a specific consequence of electron transport chain inhibition. Thus, mtDNA deletions result in cellular energy depletion, which causes the induction of AMPK and its regulated targets, and inhibit secretion of some proteins. We integrate these observations into a pathophysiological model for how mitochondrial deletions cause disease.
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PMID:Mitochondrial DNA deletions induce the adenosine monophosphate-activated protein kinase energy stress pathway and result in decreased secretion of some proteins. 1765 60

Creatine kinase (CK) is a phosphotransfer kinase that catalyzes the reversible transfer of a phosphate moiety between ADP and creatine and that is highly expressed in skeletal muscle. In fast glycolytic skeletal muscle, deletion of the cytosolic M isoform of CK in mice (M-CK-/-) leads to a massive increase in the oxidative capacity and of mitochondrial volume. This study was aimed at investigating the transcriptional pathways leading to mitochondrial biogenesis in response to CK deficiency. Wild type and M-CK-/- mice of eleven months of age were used for this study. Gastrocnemius muscles of M-CK-/- mice exhibited a dramatic increase in citrate synthase (+120%) and cytochrome oxidase (COX, +250%) activity, and in mitochondrial DNA (+60%), showing a clear activation of mitochondrial biogenesis. Similarly, mRNA expression of the COXI (mitochondria-encoded) and COXIV (nuclear-encoded) subunits were increased by +103 and +94% respectively. This was accompanied by an increase in the expression of the nuclear respiratory factor (NRF2alpha) and the mitochondrial transcription factor (mtTFA). Expression of the co-activator PGC-1alpha, a master gene in mitochondrial biogenesis was not significantly increased while that of PGC-1beta and PRC, two members of the same family, was moderately increased (+45% and +55% respectively). While the expression of the modulatory calcineurin-interacting protein 1 (MCIP1) was dramatically decreased (-68%) suggesting inactivation of the calcineurin pathway, the metabolic sensor AMPK was activated (+86%) in M-CK-/- mice. These results evidence that mitochondrial biogenesis in response to a metabolic challenge exhibits a unique pattern of regulation, involving activation of the AMPK pathway.
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PMID:Mitochondrial biogenesis in fast skeletal muscle of CK deficient mice. 1805 21

The thiazolidinedione anti-diabetic drugs increase activation of endothelial nitric-oxide (NO) synthase by phosphorylation at Ser-1177 and increase NO bioavailability, yet the molecular mechanisms that underlie this remain poorly characterized. Several protein kinases, including AMP-activated protein kinase, have been demonstrated to phosphorylate endothelial NO synthase at Ser-1177. In the current study we determined the role of AMP-activated protein kinase in rosiglitazone-stimulated NO synthesis. Stimulation of human aortic endothelial cells with rosiglitazone resulted in the time- and dose-dependent stimulation of AMP-activated protein kinase activity and NO production with concomitant phosphorylation of endothelial NO synthase at Ser-1177. Rosiglitazone stimulated an increase in the ADP/ATP ratio in endothelial cells, and LKB1 was essential for rosiglitazone-stimulated AMPK activity in HeLa cells. Infection of endothelial cells with a virus encoding a dominant negative AMP-activated protein kinase mutant abrogated rosiglitazone-stimulated Ser-1177 phosphorylation and NO production. Furthermore, the stimulation of AMP-activated protein kinase and NO synthesis by rosiglitazone was unaffected by the peroxisome proliferator-activated receptor-gamma inhibitor GW9662. These studies demonstrate that rosiglitazone is able to acutely stimulate NO synthesis in cultured endothelial cells by an AMP-activated protein kinase-dependent mechanism, likely to be mediated by LKB1.
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PMID:Rosiglitazone stimulates nitric oxide synthesis in human aortic endothelial cells via AMP-activated protein kinase. 1830 14

The effect of chronic hypobaric hypoxia (1/2 atmospheric pressure) on high energy phosphate (HEP) compounds was investigated in slow (soleus; SOL) and fast twitch (extensor digitorum longus; EDL) muscle from 3 strains of mice with large differences in hypoxic exercise tolerance (HET). Phosphocreatine concentration ([PCr]) decreased 16-29% following hypoxia in EDL and SOL in all strains, while [ADP] and [AMP] increased. In the EDL, HET was negatively correlated with the PCr/ATP ratio and positively correlated with the ATP/P(i) ratio. The free energy of ATP hydrolysis (DeltaG(obs)) remained constant despite the substantial changes that occurred in HEP profiles. The alteration of HEP set points and preservation of DeltaG(obs) are consistent with the notion that (1) maximal rates of steady-state ATP turnover are reduced under hypoxia, and (2) HEP perturbations during rest to work transitions are reduced in skeletal muscle from hypoxia acclimated animals. We therefore expected a lower phosphorylation ratio of AMP-activated protein kinase (AMPK-P/AMPK) during stimulation in hypoxic acclimated animals. However, neither the resting nor stimulated AMPK-P/AMPK was influenced by hypoxia, although there were significant differences among strains.
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PMID:High energy phosphate concentrations and AMPK phosphorylation in skeletal muscle from mice with inherited differences in hypoxic exercise tolerance. 1910 Mar 34

A wide variety of agents activate AMPK, but in many cases the mechanisms remain unclear. We generated isogenic cell lines stably expressing AMPK complexes containing AMP-sensitive (wild-type, WT) or AMP-insensitive (R531G) gamma2 variants. Mitochondrial poisons such as oligomycin and dinitrophenol only activated AMPK in WT cells, as did AICAR, 2-deoxyglucose, hydrogen peroxide, metformin, phenformin, galegine, troglitazone, phenobarbital, resveratrol, and berberine. Excluding AICAR, all of these also inhibited cellular energy metabolism, shown by increases in ADP:ATP ratio and/or by decreases in cellular oxygen uptake measured using an extracellular flux analyzer. By contrast, A769662, the Ca(2+) ionophore, A23187, osmotic stress, and quercetin activated both variants to varying extents. A23187 and osmotic stress also increased cytoplasmic Ca(2+), and their effects were inhibited by STO609, a CaMKK inhibitor. Our approaches distinguish at least six different mechanisms for AMPK activation and confirm that the widely used antidiabetic drug metformin activates AMPK by inhibiting mitochondrial respiration.
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PMID:Use of cells expressing gamma subunit variants to identify diverse mechanisms of AMPK activation. 2051 26

The mechanism for how metformin activates AMPK (AMP-activated kinase) was investigated in isolated skeletal muscle L6 cells. A widely held notion is that inhibition of the mitochondrial respiratory chain is central to the mechanism. We also considered other proposals for metformin action. As metabolic pathway markers, we focused on glucose transport and fatty acid oxidation. We also confirmed metformin actions on other metabolic processes in L6 cells. Metformin stimulated both glucose transport and fatty acid oxidation. The mitochondrial Complex I inhibitor rotenone also stimulated glucose transport but it inhibited fatty acid oxidation, independently of metformin. The peroxynitrite generator 3-morpholinosydnonimine stimulated glucose transport, but inhibited fatty acid oxidation. Addition of the nitric oxide precursor arginine to cells did not affect glucose transport. These studies differentiate metformin from inhibition of mitochondrial respiration and from active nitrogen species. Knockdown of adenylate kinase also failed to affect metformin stimulation of glucose transport. Hence, any means of increase in ADP appears not to be involved in the metformin mechanism. Knockdown of LKB1, an upstream kinase and AMPK activator, did not affect metformin action. Having ruled out existing proposals, we suggest a new one: metformin might increase AMP through inhibition of AMP deaminase (AMPD). We found that metformin inhibited purified AMP deaminase activity. Furthermore, a known inhibitor of AMPD stimulated glucose uptake and fatty acid oxidation. Both metformin and the AMPD inhibitor suppressed ammonia accumulation by the cells. Knockdown of AMPD obviated metformin stimulation of glucose transport. We conclude that AMPD inhibition is the mechanism of metformin action.
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PMID:Metformin activates AMP kinase through inhibition of AMP deaminase. 2105 55


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