In vivo response of skeletal muscle glycogen phosphorylase, phosphorylase b kinase and cyclic AMP to epinephrine administration

1962 ◽  
Vol 9 (4) ◽  
pp. 293-296 ◽  
Author(s):  
Jerome B. Posner ◽  
Robert Stern ◽  
Edwin G. Krebs
Keyword(s):  
Skeletal Muscle ◽  
Cyclic Amp ◽  
Muscle Glycogen ◽  
Glycogen Phosphorylase ◽  
Epinephrine Administration ◽  
Skeletal Muscle Glycogen

Skeletal muscle glycogen phosphorylase is irreversibly inhibited by mercury: Molecular, cellular and kinetic aspects

FEBS Letters ◽  
2013 ◽  
Vol 588 (1) ◽  
pp. 138-142 ◽  
Author(s):  
Ximing Xu ◽  
Cécile Mathieu ◽  
Solène Emmanuelle Boitard ◽  
Julien Dairou ◽  
Jean-Marie Dupret ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Muscle Glycogen ◽  
Glycogen Phosphorylase ◽  
Skeletal Muscle Glycogen

Skeletal muscle glycogen phosphorylase akinetics: effects of adenine nucleotides and caffeine

2001 ◽  
Vol 91 (5) ◽  
pp. 2071-2078 ◽  
Author(s):  
James W. E. Rush ◽  
Lawrence L. Spriet
Keyword(s):  
Skeletal Muscle ◽  
Muscle Glycogen ◽  
Glycogen Phosphorylase ◽  
Adenine Nucleotides ◽  
Dependent Manner ◽  
Skeletal Muscle Glycogen ◽  
Sparing Effect ◽  
Dose Dependent ◽  
Glycogen Sparing

This study aimed to determine physiologically relevant kinetic and allosteric effects of Pi, AMP, ADP, and caffeine on isolated skeletal muscle glycogen phosphorylase a (Phos a). In the absence of effectors, Phos a had V max = 221 ± 2 U/mg and K m = 5.6 ± 0.3 mM Pi at 30°C. AMP and ADP each increased Phos a V max and decreased K m in a dose-dependent manner. AMP was more effective than ADP (e.g., 1 μM AMP vs. ADP: V max = 354 ± 2 vs. 209 ± 8 U/mg, and K m = 2.3 ± 0.1 vs. 4.1 ± 0.3 mM). Both nucleotides were relatively more effective at lower Pi levels. Experiments simulating a range of contraction (exercise) conditions in which Pi, AMP, and ADP were used at appropriate physiological concentrations demonstrated that each agent singly and in combination influences Phos a activity. Caffeine (50–100 μM) inhibited Phos a( K m ∼8–14 mM, ∼40–50% reduction in activity at 2–10 mM Pi). The present in vitro data support a possible contribution of substrate (Pi) and allosteric effects to Phos a regulation in many physiological states, independent of covalent modulation of the percentage of total Phos in the Phos a form and suggest that caffeine inhibition of Phos a activity may contribute to the glycogen-sparing effect of caffeine.

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