ملكــة الصــمت
12-14-2006, 05:05 PM
Muscular Activity and the Cori Cycle:
Muscular activity or its anticipation leads to the release of epinephrine by the adrenal medulla. Epinephrine markedly stimulates glycogen breakdown(glycogenolysis) in muscles and, to a lesser extent, in the liver. Muscular activity quickly uses stored ATP as the energy source and more ATP must be generated by the breakdown of glycogen. The sequence of epinephrine stimulating events is outlined in the graphic on the left and explained in the following sections.
The reaction cascade sequence is as follows:
1) Epinephrine binds to a receptor on the muscle cell membrane and stimulates adenyl cyclase in the membrane.
2) Adenyl cyclase in the membrane catalyzes the formation of cyclic AMP from ATP.
3) The increase of cyclic AMP activates a protein kinase. The binding of cyclic AMP to an enzyme is an allosteric control where the enzyme is "switched on" for activity.
4) The protein kinase causes phosphorylations (addition of phosphate) on a series of phosphorylation enzymes which activates them to finally produce glucose-1-phosphate.
4a) At the same time that enzymes are being activated for glycogen breakdown, glycogen synthetase enzyme must be inactivated. Glycogenesis must be "switched off" and glycogenolysis "switched on."
5) Glucose-6-phosphate is the final result of the initial stimulation by epinephrine or other hormones such as glucagon. If this happened to a muscle cell, then the glycolysis pathway is the next step in the sequence. If this happened to a liver cell stimulated by glucagon, then glucose is produced to enter the blood stream.
http://www.elmhurst.edu/~chm/vchembook/images/615cascade.gif
Muscular activity or its anticipation leads to the release of epinephrine by the adrenal medulla. Epinephrine markedly stimulates glycogen breakdown(glycogenolysis) in muscles and, to a lesser extent, in the liver. Muscular activity quickly uses stored ATP as the energy source and more ATP must be generated by the breakdown of glycogen. The sequence of epinephrine stimulating events is outlined in the graphic on the left and explained in the following sections.
The reaction cascade sequence is as follows:
1) Epinephrine binds to a receptor on the muscle cell membrane and stimulates adenyl cyclase in the membrane.
2) Adenyl cyclase in the membrane catalyzes the formation of cyclic AMP from ATP.
3) The increase of cyclic AMP activates a protein kinase. The binding of cyclic AMP to an enzyme is an allosteric control where the enzyme is "switched on" for activity.
4) The protein kinase causes phosphorylations (addition of phosphate) on a series of phosphorylation enzymes which activates them to finally produce glucose-1-phosphate.
4a) At the same time that enzymes are being activated for glycogen breakdown, glycogen synthetase enzyme must be inactivated. Glycogenesis must be "switched off" and glycogenolysis "switched on."
5) Glucose-6-phosphate is the final result of the initial stimulation by epinephrine or other hormones such as glucagon. If this happened to a muscle cell, then the glycolysis pathway is the next step in the sequence. If this happened to a liver cell stimulated by glucagon, then glucose is produced to enter the blood stream.
http://www.elmhurst.edu/~chm/vchembook/images/615cascade.gif