When phosphorylated at Thr148, the β2-subunit of AMP-activated kinase does not associate with glycogen in skeletal muscle.
The 5'-AMP-activated protein kinase (AMPK), a heterotrimeric complex that functions as an intracellular fuel sensor that affects metabolism, is activated in skeletal muscle in response to exercise and utilization of stored energy. The diffusibility properties of α- and β-AMPK were examined in isolated skeletal muscle fiber segments dissected from rat fast-twitch extensor digitorum longus and oxidative soleus muscles from which the surface membranes were removed by mechanical dissection. After the muscle segments were washed for 1 and 10 min, ∼60% and 75%, respectively, of the total AMPK pools were found in the diffusible fraction. After in vitro stimulation of the muscle, which resulted in an ∼80% decline in maximal force, 20% of the diffusible pool became bound in the fiber. This bound pool was not associated with glycogen, as determined by addition of a wash step containing amylase. Stimulation of extensor digitorum longus muscles resulted in 28% glycogen utilization and a 40% increase in phosphorylation of the downstream AMPK target acetyl carboxylase-CoA. This, however, had no effect on the proportion of total β2-AMPK that was phosphorylated in whole muscle homogenates measured by immunoprecipitation. These findings suggest that, in rat skeletal muscle, β2-AMPK is not associated with glycogen and that activation of AMPK by muscle contraction does not dephosphorylate β2-AMPK. These findings question the physiological relevance of the carbohydrate-binding function of β2-AMPK in skeletal muscle.
Department of Biochemistry and Genetics, La Trobe Institute for Molecular Science, La Trobe University, Melbourne, Victoria, Australia;
Hongyang
H
Xu
Department of Biochemistry and Genetics, La Trobe Institute for Molecular Science, La Trobe University, Melbourne, Victoria, Australia;
Noni T
NT
Frankenberg
School of Life Sciences, La Trobe University, Melbourne, Victoria, Australia; and.
Graham D
GD
Lamb
Department of Biochemistry, University of Melbourne, Melbourne, Victoria, Australia.
Paul R
PR
Gooley
Department of Biochemistry, University of Melbourne, Melbourne, Victoria, Australia.
David I
DI
Stapleton
Department of Biochemistry and Genetics, La Trobe Institute for Molecular Science, La Trobe University, Melbourne, Victoria, Australia; r.murphy@latrobe.edu.au.
Robyn M
RM
Murphy
D055372:AMP-Activated Protein Kinases / Q000378:metabolism*; D000103:Acetyl-CoA Carboxylase / Q000378:metabolism; D000818:Animals; D004558:Electric Stimulation; D004734:Energy Metabolism; D006003:Glycogen / Q000378:metabolism*; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction; D018656:Muscle Fibers, Fast-Twitch / Q000201:enzymology*; D010766:Phosphorylation; D011485:Protein Binding; D021122:Protein Subunits; D017207:Rats, Sprague-Dawley; D013912:Threonine; D013997:Time Factors
D021122:Protein Subunits; D013912:Threonine; D006003:Glycogen; D055372:AMP-Activated Protein Kinases; C000619647:Prkab2 protein, Rat; D000103:Acetyl-CoA Carboxylase
5′-AMP-activated protein kinase; carbohydrate binding motif; glycogen association; skeletal muscle