Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.11.31 (AMP-activated protein kinase)
 13,065 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We determined whether the cell permeable molecule AICAR, whose metabolite activates AMP-activated protein kinase (AMPK) in cells, affected glycogen metabolism in rat soleus muscle preparations in vitro. The basal and insulin-stimulated rates of radiochemical lactate formation, net lactate release and glycogen synthesis were determined. AICAR stimulated net lactate release (but not radiochemical lactate formation) only at a basal concentration of insulin. An increased rate of glycogenolysis was the likely cause of increased net lactate release as glycogen phosphorylase activity was significantly increased by AICAR. AICAR-stimulated net lactate release and phosphorylase activity were potently inhibited by insulin.
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PMID:Activation of glycogen phosphorylase and glycogenolysis in rat skeletal muscle by AICAR--an activator of AMP-activated protein kinase. 861 61

AMP-activated protein kinase (AMPK) is proposed to stimulate fat and carbohydrate catabolism to maintain cellular energy status. Recent studies demonstrate that pharmacologic activation of AMPK and mutations in the enzyme are associated with elevated muscle glycogen content in vivo. Our purpose was to determine the mechanism for increased muscle glycogen associated with AMPK activity in vivo. AMPK activity and glycogen metabolism were studied in red and white gastrocnemius muscles from rats treated with 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) in vivo, and also in muscles incubated with AICAR in vitro. In vivo AICAR treatment reduced blood glucose and increased blood lactate compared with basal values. AICAR increased muscle alpha2 AMPK activity, glycogen, and glucose-6-phosphate concentrations. Glycogen synthase activity was increased in the red gastrocnemius but was decreased in the white gastrocnemius. Glycogen phosphorylase activity increased in both muscles, with an inhibition initially observed in the red gastrocnemius. In vitro incubation with AICAR activated alpha2 AMPK but had no effect on either glycogen synthase or glycogen phosphorylase. These results suggest that AICAR treatment does not promote glycogen accumulation in skeletal muscle in vivo by altering glycogen synthase and glycogen phosphorylase. Rather, the increased glycogen is due to the well-known effects of AICAR to increase glucose uptake.
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PMID:Effect of AICAR treatment on glycogen metabolism in skeletal muscle. 1187 52

We report here use of human myoblasts in culture to study the relationships between cellular glycogen concentrations and the activities of glycogen synthase (GS) and AMP-activated protein kinase (AMPK). Incubation of cells for 2 h in the absence of glucose led to a 25% decrease in glycogen content and a significant decrease in the fractional activity of GS. This was accompanied by stimulation of both the alpha1 and alpha2 isoforms of AMPK, without significant alterations in the ratios of adenine nucleotides. When glucose was added to glycogen-depleted cells, a rapid and substantial increase in GS activity was accompanied by inactivation of AMPK back to basal values. Inclusion of the glycogen phosphorylase inhibitor, CP-91149, prevented the loss of glycogen during glucose deprivation but not the activation of AMPK. However, in the absence of prior glycogen breakdown, glucose treatment failed to activate GS above control values, indicating the crucial role of glycogen content. Activation of AMPK by either 5-aminoimidazole-4-carboxamide 1-beta-D-ribofuranoside (AICAR) or hydrogen peroxide was also associated with a decrease in the activity ratio of GS. AICAR treatment had no effect on total cellular glycogen content but led to a modest increase in glucose uptake. These data support a role for AMPK in both stimulating glucose uptake and inhibiting GS in intact cells, thus promoting glucose flux through glycolysis.
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PMID:Regulation of glycogen synthase by glucose and glycogen: a possible role for AMP-activated protein kinase. 1250 87

We tested the hypothesis that activation of AMP-activated protein kinase (AMPK) promotes myocardial glycogenolysis by decreasing glycogen synthase (GS) and/or increasing glycogen phosphorylase (GP) activities. Isolated working hearts from halothane-anesthetized male Sprague-Dawley rats perfused in the absence or presence of 0.8 or 1.2 mM 5-aminoimidazole-4-carboxamide 1-beta-d-ribofuranoside (AICAR), an adenosine analog and cell-permeable activator of AMPK, were studied. Glycogen degradation was increased by AICAR, while glycogen synthesis was not affected. AICAR increased myocardial 5-aminoimidazole-4-carboxamide 1-beta-d-ribofuranotide (ZMP), the active intracellular form of AICAR, but did not alter the activity of GS and GP measured in tissue homogenates or the content of glucose-6-phosphate and adenine nucleotides in freeze-clamped tissue. Importantly, the calculated intracellular concentration of ZMP achieved in this study was similar to the K(m) value of ZMP for GP determined in homogenates of myocardial tissue. We conclude that the data are consistent with allosteric activation of GP by ZMP being responsible for the glycogenolysis caused by AICAR in the intact rat heart.
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PMID:5-Aminoimidazole-4-carboxamide 1-beta -D-ribofuranoside (AICAR) stimulates myocardial glycogenolysis by allosteric mechanisms. 1262 60

AMP-activated protein kinase (AMPK) is a multisubstrate enzyme activated by increases in AMP during metabolic stress caused by exercise, hypoxia, lack of cell nutrients, as well as hormones, including adiponectin and leptin. Furthermore, metformin and rosiglitazone, frontline drugs used for the treatment of type II diabetes, activate AMPK. Mammalian AMPK is an alphabetagamma heterotrimer with multiple isoforms of each subunit comprising alpha1, alpha2, beta1, beta2, gamma1, gamma2, and gamma3, which have varying tissue and subcellular expression. Mutations in the AMPK gamma subunit cause glycogen storage disease in humans, but the molecular relationship between glycogen and the AMPK/Snf1p kinase subfamily has not been apparent. We show that the AMPK beta subunit contains a functional glycogen binding domain (beta-GBD) that is most closely related to isoamylase domains found in glycogen and starch branching enzymes. Mutation of key glycogen binding residues, predicted by molecular modeling, completely abolished beta-GBD binding to glycogen. AMPK binds to glycogen but retains full activity. Overexpressed AMPK beta1 localized to specific mammalian subcellular structures that corresponded with the expression pattern of glycogen phosphorylase. Glycogen binding provides an architectural link between AMPK and a major cellular energy store and juxtaposes AMPK to glycogen bound phosphatases.
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PMID:AMPK beta subunit targets metabolic stress sensing to glycogen. 1274 37

The experimental evaluation of the contribution of glycogen phosphorylase (GP) to biochemical pathways is limited to methods that raise cAMP, activating the cAMP-dependent protein kinase/phosphorylase kinase/GP cascade. Such methods convert the unphosphorylated form, "GPb," which catalyzes glycogenolysis only in the presence of appropriate allosteric activators such as AMP, to the phosphorylated, constitutively activated form, "GPa." However, activation of GP in this way is indirect, requires a functional cAMP kinase cascade, and is complicated by other actions of cAMP. Here, we demonstrate a strategy for the experimental manipulation of GP in intact dermal fibroblasts, involving activation by the membrane-permeable adenosine analog 5-aminoimidazole-4-carboxamide riboside (AICAR) and inhibition by caffeine and Pfizer compound CP-91149, which bind to GP at distinct sites. Potential complications because of activation of AMP-activated protein kinase by AICAR were assessed with metformin, which activates this kinase but does not activate GP. Using this strategy, we show that glycogen can be a significant and regulatable precursor of mannosyl units in lipid-linked oligosaccharides and glycoproteins.
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PMID:Activation of glycogen phosphorylase with 5-aminoimidazole-4-carboxamide riboside (AICAR). Assessment of glycogen as a precursor of mannosyl residues in glycoconjugates. 1472 64

Postmortem glycolysis is directly linked to the incidences of PSE (pale, soft, and exudative) and DFD (dark, firm, and dry) meats, which cause significant economic loss to the meat industry. However, mechanisms controlling postmortem glycolysis are unclear. The objective of this study was to determine the role of beta-adrenoceptor signaling and AMP-activated protein kinase (AMPK) in postmortem glycolysis. Eighteen 2 month old C57BL/6J female mice were randomly separated into three groups. Group I received an intraperitoneal injection of saline solution only and served as the control; group II received a saline injection and then were forced to swim for 1 min; and group III received an injection of propranolol (1 mg/kg) in saline. In addition, six C57BL/6J female AMPK knockout mice were assigned to group IV, which received a saline injection and were forced to swim for 1 min. The longissimus dorsi muscle was sampled at 0, 1, and 24 h postmortem for pH and enzyme activity measurements. The objective is to elucidate the roles of beta-adrenoceptor signaling and AMPK in the glycolysis of postmortem muscle. Results showed that AMPK activity had a major role in determining the ultimate muscle pH, with an ultimate pH for control mice of 6.16 and AMPK knockout mice of 6.48. The beta-adrenoceptor signaling is essential for initial rapid glycolysis. Blocking beta-adrenoceptor signaling prevented the initial pH decline induced by stress. Activation of beta-adrenoceptor signaling due to preslaughter stress activates glycogen phosphorylase, resulting in a rapid glycolysis shortly after slaughter. On the other hand, the activation of AMPK is important for maintaining the activity of glycogen phosphorylase and pyruvate kinase, leading to a sustained glycolysis and a low ultimate pH.
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PMID:Role of beta-adrenoceptor signaling and AMP-activated protein kinase in glycolysis of postmortem skeletal muscle. 1582 83

Fatal congenital nonlysosomal cardiac glycogenosis has been attributed to a subtype of phosphorylase kinase deficiency, but the underlying genes and mutations have not been identified. Analyzing four sporadic, unrelated patients, we found no mutations either in the eight genes encoding phosphorylase kinase subunits or in the two genes encoding the muscle and brain isoforms of glycogen phosphorylase. However, in three of five patients, we identified identical heterozygous R531Q missense mutations of the PRKAG2 gene, which encodes the gamma 2-subunit of AMP-activated protein kinase, a key regulator of energy balance. Biochemical characterization of the recombinant R531Q mutant protein showed >100-fold reduction of binding affinities for the regulatory nucleotides AMP and ATP but an enhanced basal activity and increased phosphorylation of the alpha -subunit. Other PRKAG2 missense mutations were previously identified in patients with autosomal dominant hypertrophic cardiomyopathy with Wolff-Parkinson-White syndrome, characterized by juvenile-to-adult clinical onset, moderate cardiac glycogenosis, disturbed excitation conduction, risk of sudden cardiac death in midlife, and molecular perturbations that are similar to--but less severe than--those observed for the R531Q mutation. Thus, recurrent heterozygous R531Q missense mutations in PRKAG2 give rise to a massive nonlysosomal cardiac glycogenosis of fetal symptomatic onset and rapidly fatal course, constituting a genotypically and clinically distinct variant of hypertrophic cardiomyopathy with Wolff-Parkinson-White syndrome. R531Q and other PRKAG2 mutations enhance the basal activity and alpha -subunit phosphorylation of AMP-activated protein kinase, explaining the dominant nature of PRKAG2 disease mutations. Since not all cases displayed PRKAG2 mutations, fatal congenital nonlysosomal cardiac glycogenosis seems to be genetically heterogeneous. However, the existence of a heart-specific primary phosphorylase kinase deficiency is questionable, because no phosphorylase kinase mutations were found.
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PMID:Fatal congenital heart glycogenosis caused by a recurrent activating R531Q mutation in the gamma 2-subunit of AMP-activated protein kinase (PRKAG2), not by phosphorylase kinase deficiency. 1587 79

AMP-activated protein kinase (AMPK) is a heterotrimeric complex that works as an energy sensor to integrate nutritional and hormonal signals. The naturally occurring R225Q mutation in the gamma3-subunit in pigs is associated with abnormally high glycogen content in skeletal muscle. Because skeletal muscle accounts for most of the body's glucose uptake, and gamma3 is specifically expressed in skeletal muscle, it is important to understand the underlying mechanism of this mutation in regulating glucose and glycogen metabolism. Using skeletal muscle-specific transgenic mice overexpressing wild type gamma3 (WTgamma3) and R225Q mutant gamma3 (MUTgamma3), we show that both WTgamma3 and MUTgamma3 mice have 1.5- to 2-fold increases in muscle glycogen content. In WTgamma3 mice, increased glycogen content was associated with elevated total glycogen synthase activity and reduced glycogen phosphorylase activity, whereas alterations in activities of these enzymes could not explain elevated glycogen in MUTgamma3 mice. Basal, 5-aminoimidazole-AICAR- and phenformin-stimulated AMPKalpha2 isoform-specific activities were decreased only in MUTgamma3 mice. Basal rates of 2-DG glucose uptake were decreased in both WTgamma3 and MUTgamma3 mice. However, AICAR- and phenformin-stimulated 2-DG glucose uptake were blunted only in MUTgamma3 mice. In conclusion, expression of either wild type or mutant gamma3-subunit of AMPK results in increased glycogen concentrations in muscle, but the mechanisms underlying this alteration appear to be different. Furthermore, mutation of the gamma3-subunit is associated with decreases in AMPKalpha2 isoform-specific activity and impairment in AICAR- and phenformin-stimulated skeletal muscle glucose uptake.
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PMID:Muscle-specific overexpression of wild type and R225Q mutant AMP-activated protein kinase gamma3-subunit differentially regulates glycogen accumulation. 1663 25

Pale, soft, and exudative (PSE) meat has been recognized for decades. Fast glycolysis during early post-mortem stage while the muscle temperature is still high is the cause of PSE meat. To elucidate the molecular mechanism underlying this fast glycolysis in muscle to become PSE meat, post-mortem ATP metabolism, fructose-2,6-diphosphate content, and the activities of AMPK, glycogen phosphorylase, and pyruvate kinase were examined in post-mortem muscle. Earlier and faster post-mortem AMPK activation was responsible for the significantly lower pH and higher lactic acid accumulation (p<0.05) seen in PSE muscle, which resulted in the occurrence of PSE meat. In muscle that became PSE meat, AMPK was activated at 0 h post-mortem and reached maximal activation at 0.5 h post-mortem, whereas AMPK reached maximal activation at 1 h post-mortem in the normal pork loin. Higher fructose-2,6-diphosphate content (p<0.05) was detected in PSE muscle compared to normal muscle at early post-mortem stage. However, no difference in the activities of glycogen phosphorylase and pyruvate kinase, rate-controlling enzymes in glycogenolysis and glycolysis, respectively, was detected between PSE and normal pork loins. Because fructose-2,6-diphosphate is a product of phosphofructokinase-2 (PFK-2), these data suggest that AMPK regulates post-mortem glycolysis through its phosphorylation and activation of PFK-2, which then up-regulates the activity of phosphofructokinase-1 (PFK-1), a key rate-controlling enzyme in glycolysis. Early AMPK activation in PSE muscle is associated with early consumption of ATP, because higher AMP and IMP contents and lower ATP content were detected in PSE meat compared to normal meat. Other mechanisms causing early AMPK activation in PSE meat may exist, which warrants further investigation.
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PMID:Early post-mortem AMP-activated protein kinase (AMPK) activation leads to phosphofructokinase-2 and -1 (PFK-2 and PFK-1) phosphorylation and the development of pale, soft, and exudative (PSE) conditions in porcine longissimus muscle. 1684 49


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