Glycogen metabolic role

Be Pyridoxine, pyridoxal, pyridoxamine Coenzyme in transamination and decarboxylation of amino acids and glycogen phosphorylase role in steroid hormone action Disorders of amino acid metabolism, convulsions... 

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. 

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. 

Liver tissue contains an array of cell types, but the preponderant one is the hepatocyte. It has an overall structure much like that of the cell in Fig. 1-3. The cells are arranged in long, branching columns of about 20 cells in a cross section around a central bile cannaliculus (channel). Into the cannaliculus the cells secrete bile. The liver is the main producer of urea (Chap. 15), stores glycogen (Chap. 11). synthesizes many of the amino acids used by other tissues (Chap. 3), and produces serum proteins, among many other metabolic roles. 

A. R Saltiel. The paradoxical regulation of protein phosphorylation in insulin action. FASEBJ, 8, (13), 1034-1040, 1994. Also J. A. Printen, M. J. Brady, A. R Saltiel. PTG, a protem phosphatase 1-binding protein with a role in glycogen metabolism. Science, T1S, 1475-1478, 1997. 

GSK-3 was originally described for its role in metabohc pathways as a kinase phosphorylating and inactivating glycogen synthase (GS) in skeletal muscle [9]. Today, it is accepted that GSK-3 function is not restricted to glycogen metabolism, and GSK-3 has been shown to exert pleiotropic functions as the kinase phosphorylates numerous substrates in diverse cell types. 

Adenylate cyclase is a membrane-bound enzyme that, after stimulation by a G protein, catalyzes formation of cAMP from ATP (see below). cAMP, thus formed, stimulates activation of a kinase cascade that affects several metabolic pathways, such as glycogen metabolism (see here) and gluconeogenesis. Adenylate cyclase plays an important role in signal transduction. 

When bound to calcium, calmodulin plays a special role as an integral subunit of the glycogen metabolism enzyme, phosphorylase b kinase. Hence, the glycogenolysis cascade depends on intracellular calcium concentration as well as on cyclic AMP levels. This dependence is particularly... 

Donahue, M. J., Masaracchia, R. A. and Harris, B. G. (1983) The role of cyclic AMP-mediated regulation of glycogen metabolism in levamisole-perfused Ascaris suum muscle. Mol. Pharmacol. 23 378-383. 

Goenzymes are introduced in this chapter and are discussed in later chapters in the context of the reactions in which they play a role. Chapter 16 discusses carbohydrates. Chapter 17 begins the overview of the metabohc pathways by discussing glycolysis. Glycogen metabolism, gluconeogenesis, and the pentose phosphate pathway (Chapter 18) provide bases for treating control mechanisms in carbohydrate metabolism. Discussion of the citric acid cycle is followed by the electron transport chain and oxidative phosphorylation in Chapters 19 and 20. The catabolic and anabolic aspects of lipid metabohsm are dealt with in Chapter 21. In Chapter 22, photosynthesis rounds out the discussion of carbohydrate metabolism. Chapter... 

Explain the role of hormones in regulating glycogen metabolism. 

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