Glycogen synthase binds to sarcoplasmic reticulum and is phosphorylated by CaMKII in fast-twitch skeletal muscle

We investigated the subcellular localization of glycogen synthase (GS) in the adductor muscle of anesthetized rabbits injected intravenously with propranolol. Under these experimental conditions, glycogen content was about 10 mmol/kg of fresh tissue. Immunofluorescent and fractionation studies showe...

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Bibliographic Details
Published in:Archives of biochemistry and biophysics 2007-03, Vol.459 (1), p.115-121
Main Authors: Sacchetto, Roberta, Bovo, Elisa, Salviati, Leonardo, Damiani, Ernesto, Margreth, Alfredo
Format: Article
Language:English
Subjects:
Animals
Calcium-Calmodulin-Dependent Protein Kinase Type 2
Calcium-Calmodulin-Dependent Protein Kinases - metabolism
CaMKII
Cells, Cultured
Enzyme Activation
Exercise
Glycogen
Glycogen synthase
Glycogen Synthase - metabolism
Muscle Fibers, Fast-Twitch - metabolism
Muscle, Skeletal - metabolism
Phosphorylation
Protein Binding
Rabbits
Sarcoplasmic reticulum
Sarcoplasmic Reticulum - metabolism
Skeletal muscle
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Summary:We investigated the subcellular localization of glycogen synthase (GS) in the adductor muscle of anesthetized rabbits injected intravenously with propranolol. Under these experimental conditions, glycogen content was about 10 mmol/kg of fresh tissue. Immunofluorescent and fractionation studies showed that GS associated with sarcoplasmic reticulum (SR) membranes. Glycogen and GS always co-sedimented, suggesting a predominant role of glycogen in targeting of GS to SR. SR-associated GS was phosphorylated in vitro by SR-bound Ca 2+-calmodulin dependent protein kinase (CaMKII) and dephosphorylated by endogenous protein phosphatase 1 (PP1c). Based on measurements of GS activity ratio, in vitro phosphorylation of GS by CaMKII did not significantly affect GS activity per se. However, GS activity ratio was slightly reduced, when SR membranes were further incubated with ATP after prior phosphorylation by CaMKII, suggesting that CaMKII might act sinergistically with other protein kinases. We propose that SR-bound CaMKII plays a role in regulation of glycogen metabolism in skeletal muscle, when intracellular Ca 2+ is raised.
ISSN:0003-9861
1096-0384
DOI:10.1016/j.abb.2006.11.004