Interaction between glycogen phosphorylase and sarcoplasmic reticulum membranes and its functional implications.
Skeletal muscle glycogen phosphorylase b binds to sarcoplasmic reticulum (SR) membranes with a dissociation constant of 1.7 +/- 0.6 mg of phosphorylase/ml at 25 degrees C at physiological pH and ionic strength. Raising the temperature to 37 degrees C produced a 2-3-fold decrease in the dissociation constant. The SR membranes could bind up to 1.1 +/- 0.1 mg of glycogen phosphorylase b/mg of SR protein, whereas liposomes prepared with endogenous SR lipids and reconstituted Ca(2+)-ATPase were unable to bind glycogen phosphorylase. Binding of glycogen phosphorylase b to SR membranes is accompanied by inhibition of its activity in the presence of AMP. The Vmax for glycogen phosphorylase b associated with SR membranes is 40 +/- 5% of that for purified glycogen phosphorylase and shows a decreased affinity for its allosteric activators, AMP and IMP. These kinetic effects are also observed with purified glycogen phosphorylase b when starch or alpha-amylose is used as substrate instead of glycogen. Treatment of SR membranes with alpha-amylase produced dissociation of glycogen phosphorylase b from the SR membranes. Thus, linear polysaccharide fragments of glycogen bound to the SR membranes are likely mediating the binding of glycogen phosphorylase b to these membranes.
Cuenda
A
A
Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias, Universidad de Extremadura, Bodajoz, Spain.
Nogues
M
M
Henao
F
F
Gutiérrez-Merino
C
C
D000818:Animals; D002118:Calcium / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009124:Muscle Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010763:Phosphorylase b / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006005:Phosphorylases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011485:Protein Binding; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*
D009124:Muscle Proteins; D010763:Phosphorylase b; D006005:Phosphorylases; D000252:Calcium-Transporting ATPases; D002118:Calcium