Glycogen metabolic control

The principal enzymes controlling glycogen metabolism—glycogen phosphorylase and glycogen synthase— are regulated by allosteric mechanisms and covalent modifications due to reversible phosphorylation and... 

Hormones and neuronal activity affect brain glycogen metabolism. Glycogen is affected by hormones endogenous to the brain including vasoactive intestinal peptide and noradrenaline, as well as circulating hormones, such as insulin [61, 63, 64]. The mechanism whereby insulin exerts an effect on glycogen metabolism in brain has not been determined [63]. Glycogen metabolism in brain, unlike in other tissues, is controlled locally, due to differential local metabolic rates. 

This sort of control is usually achieved by either covalent modification (phosphorylation or de phosphorylation as in glycogen metabolism) or by proteolytic cleavage (e.g. activation of digestive enzymes in the gut, or blood clotting mechanism. 

The switch in the action of the enzyme between its kinase and phosphatase activities is brought about by phosphorylation mediated by the serine/threonine protein kinase A (PKA), the same cAMP dependent enzyme which plays a role in the control of glycogen metabolism. In its kinase form, PFK-2 is dephosphorylated but phosphorylated in the phosphatase form. 

Let s get back to glucose as energy source and consider a far more complex example of metabolic control. As noted above, glucose can be oxidized with the release of energy when it is required or stored as glycogen in liver or muscle when it is not. So what determines what happens ... 

The current state of Ser/Thr phosphorylation of a protein is determined by the relative activity of Ser/Thr-specific protein kinase and protein phosphatase. It is therefore imderstandable that the cell has had to develop special mechanisms to balance the two activities with one another, and, when needed, to allow kinase or phosphatase activity to dominate. One of the best investigated examples of coordinated activity of protein kinases and protein phosphatases is the regulation of glycogen metabolism in skeletal muscle. Glycogen metabolism is an example of how two different signals, namely a cAMP signal and a Ca signal meet in one metabolic pathway and control the activity of one and the same enzyme. 

Alston, S., Hampson, L., Gomez-Foix, A.M., Gninovart, J.J., Aglus, L. (2001) Hepatic glycogen synthesis is highly sensitive to phosphorylase activity evidence from metabolic control analysis. J. Biol. Chem. 276, 23,858-23,866. 

Review of the use of NMR to measure metabolite concentrations during glycogen synthesis, interpreted by metabolic control analysis. 

All these compounds arc selective inhibitors of the serine/threo nine phosphatases PP1 and PP2A.4 Phosphatases catalyze the hydrolysis of phosphates bound to serine or threonine OH groups in en/ymesT and hydrolysis of this type causes the en/ymes to be activated or deactivated. Among other functions these en/ymes play a role in the regulation and control of glycogen metabolism. 

Related topics Membrane lipids (El) Cholesterol (K5) Membrane protein and Nerve (N3) carbohydrate (E2) Control of glycogen metabolism 07)... 

Hormonal control Glycogen metabolism is tightly controlled by hormones. When blood glucose by epinephrine levels fall, glucagon is secreted by the a cells of the pancreas and acts on the and glucagon liver to stimulate glycogen breakdown to glucose which is then released into... 

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