scholarly journals Dephosphorylation and activation of exogenous glycogen synthase by adipose-tissue phosphatase

1980 ◽  
Vol 188 (1) ◽  
pp. 221-228 ◽  
Author(s):  
Joan Heller Brown ◽  
Ronald D. Eichner ◽  
Barbara Thompson ◽  
Steven Mayer
Keyword(s):  
Skeletal Muscle ◽  
Adipose Tissue ◽  
Protein Kinase ◽  
Phosphatase Activity ◽  
Muscle Glycogen ◽  
Glycogen Synthase ◽  
Enzyme Activation ◽  
Phosphoprotein Phosphatase ◽  
Tissue Extracts ◽  
Lag Period

Exogenous purified rabbit skeletal-muscle glycogen synthase was used as a substrate for adipose-tissue phosphoprotein phosphatase from fed and starved rats in order to (1) compare the relationship between phosphate released from, and the kinetic changes imparted to, the substrate and (2) ascertain if decreases in adipose-tissue phosphatase activity account for the apparent decreased activation of endogenous glycogen synthase from starved as compared with fed rats. Muscle glycogen synthase was phosphorylated with [γ-32P]ATP and cyclic AMP-dependent protein kinase alone, or in combination with a cyclic AMP-independent protein kinase, to 1.7 or 3mol of phosphate per subunit. Adipose-tissue phosphatase activity determined with phosphorylated skeletal-muscle glycogen synthase as substrate was decreased by 35–60% as a consequence of starvation. This decrease in phosphatase activity had little effect on the capacity of adipose-tissue extracts to activate exogenous glycogen synthase (i.e. to increase the glucose 6-phosphate-independent enzyme activity), although there were marked differences in the activation profiles for the two exogenous substrates. Glycogen synthase phosphorylated to 1.7mol of phosphate per subunit was activated rapidly by adipose-tissue extracts from either fed or starved rats, and activation paralleled enzyme dephosphorylation. Glycogen synthase phosphorylated to 3mol of phosphate per subunit was activated more slowly and after a lag period, since release of the first mol of phosphate did not increase the glucose 6-phosphate-independent activity of the enzyme. These patterns of enzyme activation were similar to those observed for the endogenous adipose-tissue glycogen synthase(s): the glucose 6-phosphate-independent activity of the endogenous enzyme from fed rats increased rapidly during incubation, whereas that of starved rats, like that of the more highly phosphorylated muscle enzyme, increased only very slowly after a lag period. The observations made here suggest that (1) changes in glucose 6-phosphate-independent glycogen synthase activity are at best only a qualitative measure of phosphoprotein phosphatase activity and (2) the decrease in glycogen synthase phosphatase activity during starvation is not sufficient to explain the differential glycogen synthase activation in adipose tissue from fed and starved rats. However, alterations in the phosphorylation state of glycogen synthase combined with decreased activity of phosphoprotein phosphatase, both as a consequence of starvation, could explain the apparent markedly decreased enzyme activation.

scholarly journals The effects of food deprivation and re-feeding on bovine adipose-tissue glycogen synthase

1979 ◽  
Vol 184 (2) ◽  
pp. 229-232 ◽  
Author(s):  
R D Eichner ◽  
R J Arnold
Keyword(s):  
Adipose Tissue ◽  
Phosphatase Activity ◽  
Food Deprivation ◽  
Glycogen Content ◽  
Specific Activity ◽  
Glycogen Synthase ◽  
Glycogen Metabolism ◽  
Phosphoprotein Phosphatase ◽  
Tissue Extracts ◽  
Rat Adipose Tissue

Bovine adipose-tissue glycogen metabolism was studied during food deprivation and re-feeding. Changes in the specific activity of adipose-tissue glycogen synthase paralleled changes in tissue glycogen content: both parameters increased during food deprivation and remained so during the first 10 days of re-feeding. The values for the A0.5 (activation constant) for glucose 6-phosphate of the freshly isolated enzyme from adipose tissue from fed and starved steers were 2.9 +/- 0.1 mM and 0.90 +/- 0.05 mM respectively. Additionally, whereas incubation of adipose-tissue extracts from fed steers did not activate endogenous glycogen synthase (through a presumed phosphoprotein phosphatase mechanism), the enzyme from starved or re-fed (up to 3 days re-feeding) steers was reversibly activated as measured by changes in the value for the A0.5 for glucose 6-phosphate. Thus activation of bovine adipose-tissue glycogen synthase during food deprivation appears to be related to expression of glycogen synthase phosphatase activity. These effects of food deprivation on bovine glycogen metabolism contrast markedly with the effects observed in rat adipose tissue.

scholarly journals Effect of acute activation of 5′-AMP-activated protein kinase on glycogen regulation in isolated rat skeletal muscle

2007 ◽  
Vol 102 (3) ◽  
pp. 1007-1013 ◽  
Author(s):  
Licht Miyamoto ◽  
Taro Toyoda ◽  
Tatsuya Hayashi ◽  
Shin Yonemitsu ◽  
Masako Nakano ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Protein Kinase ◽  
Muscle Glycogen ◽  
Glycogen Synthase ◽  
Glycogen Synthesis ◽  
Glycolytic Flux ◽  
Ampk Activation ◽  
Ampk Activity ◽  
Amp Activated Protein Kinase ◽  
Isolated Rat

5′-AMP-activated protein kinase (AMPK) has been implicated in glycogen metabolism in skeletal muscle. However, the physiological relevance of increased AMPK activity during exercise has not been fully clarified. This study was performed to determine the direct effects of acute AMPK activation on muscle glycogen regulation. For this purpose, we used an isolated rat muscle preparation and pharmacologically activated AMPK with 5-aminoimidazole-4-carboxamide-1-β-d-ribonucleoside (AICAR). Tetanic contraction in vitro markedly activated the α1- and α2-isoforms of AMPK, with a corresponding increase in the rate of 3- O-methylglucose uptake. Incubation with AICAR elicited similar enhancement of AMPK activity and 3- O-methylglucose uptake in rat epitrochlearis muscle. In contrast, whereas contraction stimulated glycogen synthase (GS), AICAR treatment decreased GS activity. Insulin-stimulated GS activity also decreased after AICAR treatment. Whereas contraction activated glycogen phosphorylase (GP), AICAR did not alter GP activity. The muscle glycogen content decreased in response to contraction but was unchanged by AICAR. Lactate release was markedly increased when muscles were stimulated with AICAR in buffer containing glucose, indicating that the glucose taken up into the muscle was catabolized via glycolysis. Our results suggest that AMPK does not mediate contraction-stimulated glycogen synthesis or glycogenolysis in skeletal muscle and also that acute AMPK activation leads to an increased glycolytic flux by antagonizing contraction-stimulated glycogen synthesis.

Properties of a phosphoprotein phosphatase from rat epididymal fat pads: deactivation of hormone-sensitive triglyceride lipase and activation of glycogen synthase in adipose tissue

1980 ◽  
Vol 58 (3) ◽  
pp. 243-250 ◽  
Author(s):  
David L. Severson ◽  
Shellie Sloan
Keyword(s):  
Adipose Tissue ◽  
Phosphatase Activity ◽  
Glycogen Synthase ◽  
Adenine Nucleotides ◽  
Fat Pad ◽  
Phosphoprotein Phosphatase ◽  
Triglyceride Lipase ◽  
Epididymal Fat ◽  
Hormone Sensitive ◽  
Fat Pads

A phosphoprotein phosphatase has been partially purified from rat epididymal fat pads by a procedure utilizing ammonium sulfate and ethanol precipitations and chromatography on DEAE-Sephadex A-50. The phosphatase was eluted from Sephadex G-75 columns with an apparent molecular weight of 28 000. The phosphoprotein phosphatase catalyzed the reversible deactivation of protein kinase activated chicken adipose tissue hormone-sensitive triglyceride lipase. Phosphatase activity measured with activated triglyceride lipase as substrate was completely dependent upon the presence of metal ions (Mg2+, Ca2+, or Mn2+) and was inhibited by inorganic phosphate and adenine nucleotides. The fat pad phosphatase increased the rate of activation of glycogen synthase in rat adipose tissue infranatant fractions from fed and 24-h-fasted rats but had little or no effect on synthase activity in infranatant fractions from rats fasted for 48 h. Fasting had no effect on rat fat pad phosphatase activity measured with triglyceride lipase as substrate, but phosphatase activity was decreased in preparations from diabetic rats.

Genetic model for the chronic activation of skeletal muscle AMP-activated protein kinase leads to glycogen accumulation

2007 ◽  
Vol 292 (3) ◽  
pp. E802-E811 ◽  
Author(s):  
Laura Barré ◽  
Christine Richardson ◽  
Michael F. Hirshman ◽  
Joseph Brozinick ◽  
Steven Fiering ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Protein Kinase ◽  
Muscle Glycogen ◽  
Glycogen Content ◽  
Genetic Model ◽  
Glycogen Synthase ◽  
Dominant Negative ◽  
Α Subunit ◽  
Chronic Activation ◽  
Amp Activated Protein Kinase

The AMP-activated protein kinase (AMPK) is an important metabolic sensor/effector that coordinates many of the changes in mammalian tissues during variations in energy availability. We have sought to create an in vivo genetic model of chronic AMPK activation, selecting murine skeletal muscle as a representative tissue where AMPK plays important roles. Muscle-selective expression of a mutant noncatalytic γ1 subunit (R70Qγ) of AMPK activates AMPK and increases muscle glycogen content. The increase in glycogen content requires the presence of the endogenous AMPK catalytic α-subunit, since the offspring of cross-breeding of these mice with mice expressing a dominant negative AMPKα subunit have normal glycogen content. In R70Qγ1-expressing mice, there is a small, but significant, increase in muscle glycogen synthase (GSY) activity associated with an increase in the muscle expression of the liver isoform GSY2. The increase in glycogen content is accompanied, as might be expected, by an increase in exercise capacity. Transgene expression of this mutant AMPKγ1 subunit may provide a useful model for the chronic activation of AMPK in other tissues to clarify its multiple roles in the regulation of metabolism and other physiological processes.

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