Synthesis glycogen

Glycogen is present in virtually every cell in the body, but it is especially abundant in liver and skeletal muscle. The amount stored in tissues varies greatly in response to metabolic and physiological demands, but in a resting individual after a meal, liver usually contains roughly 4-7% of its wet weight as glycogen and muscle about 1%. 

Since the body contains 10 times more muscle than hepatic tissue, the total amount of glycogen stored in muscle is greater than that in liver. 

Glycogenesis begins with the phosphorylation of glucose by glucokinase in liver and by hexokinase in muscle and other tissues (Chapter 13)  

The second step in glycogenesis is conversion of glucose-6-phosphate to glucose-1-phosphate by phosphoglucomutase in a reaction similar to that catalyzed by phospho-glyceromutase. The phosphoryl group of the enzyme participates in this reversible reaction in which glucose-1,6-bisphosphate serves as an intermediate  

In the third step, glucose-1-phosphate is converted to uridine diphosphate (UDP) glucose, the immediate precursor of glycogen synthesis, by reaction with uridine triphosphate (UTP). This reaction is catalyzed by glucose-1-phosphate uridylyltransferase (or UDP-glucose pyrophos-phorylase)  

Glycogen is a polymer of glucose and, although most tissues contain some glycogen, quantitatively important 

To help to understand this process, it is useful to appreciate that there is a degree of similarity in the sequences of the three major synthetic processes, glycogen, fatty acid and peptide syntheses. The similarities are presented in Table 6.2. 

The ionic composition of a medium which may cause optimal glycogen formation in one tissue may not do so in other tissues. Thus K+ does not influence glycogenosis in rat diaphragm. In fact, with insulin the best effects are obtained in media lacking K+. Furthermore, in heart muscle shces optimal glycogen formation from glucose was obtained in media low in ions but high in nonionic compounds such as n-mannitol.  

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We are familiar with several examples of chemical activation as a strategy for group transfer reactions. Acetyl-CoA is an activated form of acetate, biotin and tetrahydrofolate activate one-carbon groups for transfer, and ATP is an activated form of phosphate. Luis Leloir, a biochemist in Argentina, showed in the 1950s that glycogen synthesis depended upon sugar nucleotides, which may be... 

Earner, J., 1990. Insulin and the stimulation of glycogen synthesis The road from glycogen structure to glycogen synthase to cyclic AMP-dependent protein kinase to insulin mediators. Advances in Enzymology 63 173-231. 

Glycogen synthesis 1 Muscle glycogen synthase l Activity Muscle... 

GSK3 phosphorylates glycogen synthase (GS), the key enzyme for glycogen synthesis which builds up the... 

The insulin receptor is a transmembrane receptor tyrosine kinase located in the plasma membrane of insulin-sensitive cells (e.g., adipocytes, myocytes, hepatocytes). It mediates the effect of insulin on specific cellular responses (e.g., glucose transport, glycogen synthesis, lipid synthesis, protein synthesis). 

Liver Activation of glycogen synthesis Activation of glycogen synthase (GS) Inactivation of glycogen synthase kinase 3 (GSK3) through phosphorylation by Akt... 

Bergstrom, J. Hultman, E. (1966). Muscle glycogen synthesis after exercise An enhancing factor localized to the muscle cells in man. Nature 210, 309-310. 

Hultman, E. Bergstrom, J. (1967). Muscle glycogen synthesis in relation to diet studied in normal subjects. Acta Med. Scand. 182, 109-117. 

Figure 13-13. The glycogen molecule. A General structure. B Enlargement of structure at a branch point. The molecule is a sphere approximately 21 nm in diameter that can be visualized in electron micrographs. It has a molecular mass of 10 Da and consists of polysaccharide chains each containing about 13 glucose residues. The chains are either branched or unbranched and are arranged in 12 concentric layers (only four are shown in the figure). The branched chains (each has two branches) are found in the inner layers and the unbranched chains in the outer layer. (G, glycogenin, the primer molecule for glycogen synthesis.)...

The breakdown of glycogen to glucose 1-phosphate is catalyzed by phosphorylase. Glycogen synthesis involves a different pathway via uridine diphosphate glucose and glycogen synthase (Figure 18-1). 

Lomako, J., Lomako, W.M., and Whelan, W.J. (1990) Substrate specificity of the autocatalytic protein that primes glycogen synthesis. FEBS Lett. 264 13-16. 

Regulation of glycogen synthesis and degradation is essentially the same in the liver and muscle, but there are a couple of wrinkles. Glycogen degradation is also activated in muscle in response to the rise in intracellular calcium levels that accompanies contraction. This is achieved by... 

ATPs are required to store each glucose as glycogen. Synthesis 1... 

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