Thermodynamics of Glycogen Metabolism
In response to glucagon signaling glycogen phosphorylase kinase is activated by phosphorylation by cAMP-dependent protein kinase (protein kinase a) and it turn phosphorylates glycogen phosphorylase on each monomer, converting it to the relaxed, active state.
But the muscles contain glycogen.
In addition, levels of epinephrine and norepinephrine, hormones that (among other things) stimulate glycogen mobilization, rise significantly more in men than in women during exercise.
When the level of glucose raises sufficiently glucagon secretion from the pancreas is decreased and insulin secretion is increased. The increased insulin causes activation of protein phosphatase 1, but only when the glucose level has risen sufficiently does glucose bind to each subunit of glycogen phosphorylase, causing a conformation change that makes the activating phosphates accessible to active protein phosphatase 1, which hydrolyzes them and converts glycogen phosphorylase to the inactive, tens state. The phosphatase does not bind to inactive glycogen phosphorylase, but rather is free to hydrolyze the inactivating phosphates from glycogen synthase, thereby activating it. Glucose does not bind to muscle glycogen phosphorylase and does not regulate its activity.
Integration of Glycogen Metabolism Control Mechanism
Reciprocal regulation of glycogen synthesis and glycogen degradation: Ensuring that glycogen synthesis and degradation do not occur simultaneously in a futile cycle
The liver can store excess glucose as glycogen.
Glucagon (liver) or epinephrine (β2-adrenergic receptor in muscle & liver) triggered cAMP-dependent phosphorylation cascade results in the phosphorylation of glycogen phosphorylase at serine 14, switching the it to the activated, "a" form. However, cAMP- dependent protein kinase (protein kinase A) does not phosphorylate glycogen phosphorylase directly. It phosphorylates phosphorylase kinase, converting it from the inactive "b" form" to the active "a" form. Then the active phosphorylase kinase phosphorylates glycogen phosphorylase at serine 14, converting it from the inactive "b" form to the active "a" form. At the same time cAMP-dependent protein kinase phosphorylates glycogen synthase. This has the effect of rendering the synthase susceptible to phosphorylation by several other protein kinases, which convert it from the active "a" form to the inactive "b" form.
Glycogen Biosynthesis; Glycogen Breakdown - Oregon …
Active cAMP-dependent protein kinase phosphorylates glycogen phosphorylase kinase (phosphorylase kinase), converting it from the inactive "b" for to the active "a" form. Active cAMP-dependent protein kinase phosphorylates the inhibitor 1 protein, activating it to bind to and inhibit protein phosphatase 1, and also phosphorylates protein phosphatase 1 directly, causing its inhibition. As a result the activating phosphate on phosphorylase kinase is not removed by protein phosphatase 1 and phosphorylase kinase remains active as long a glucagon or epinephrine signaling continues.
Glycogenolysis in muscle and liver - Tuscany Diet
The active form of glycogen phosphorylase kinase phosphorylates and activates glycogen phosphorylase. Active Inhibitor 1 protein and direct phosphorylation by cAMP-dependent protein kinase inhibit protein phosphatase 1, which, in its active state, removes the activating phosphate group from glycogen phosphorylase. Active glycogen phosphorylase catalyzes the sequential removal of 1 glucose molecule as glucose-1-phosphate from the non-reducing ends of glycogen.
Glycogen synthesis and breakdown are often ..
cAMP-dependent protein kinase phosphorylates glycogen synthase to make it susceptible to phosphorylation by other protein kinases that phosphorylate and inactivate it. The consequence is that when glycogen breakdown occurs, glycogen synthesis does not occur simultaneously in a futile breakdown/re-synthesis cycle.