Glycogen metabolism

Glycogen is the storage form of glucose mainly found in liver and muscle. 

Glycogen stores are regulated by a balance between glycogen synthesis (glycogenesis) and breakdown (glycogenolysis). 

Glycogen stores serve as an easily mobilized source of glucose to provide 

Phosphofructokinase-1 Fructose 6-phosphate AMP Fructose 2,6-bisphosphate Phosphoenolpyruvate ATP Citrate  

Glycogenesis occurs in response to stimulation by insulin after ingestion of a 

The first step in glycogen synthesis is the formation of glucose 1-phosphate, catalyzed by phosphoglucomutase  

The glucose 1-phosphate is then activated to enable its incorporation into glycogen. This activation involves the expenditure of energy derived from the hydrolysis of a molecule of uridine triphosphate (UTP) by UDP-glucose pyrophosphorylase. 

Question What is the origin of the two phosphate groups in UDP-glucose  

One is from glucose 1-phosphate and the other is from uridine monophosphate (UMP). The pyrophosphate that is liberated from the terminal phosphates of UTP is hydrolyzed to inorganic phosphate by the enzyme pyrophosphatase. This hydrolysis, which is irreversible, drives the reaction in the direction of UDP-glucose synthesis. 

The modified glucose molecule is a substrate for the enzyme glycogen synthase  

The human organism can store up to 450 g of glycogen—one-third in the liver and almost all of the remainder in muscle. The glycogen content of the other organs is low. 

Koolman, Color Atlas of Biochemistry, 2nd edition 2005 Thieme All rights reserved. Usage subject to terms and conditions of license. 

In all organisms, carbohydrate metabolism is subject to complex regulatory mechanisms involving hormones, metabolites, and coenzymes. The scheme shown here (still a simplified one) applies to the liver, which has central functions in carbohydrate metabolism (see p. 306). Some of the control mechanisms shown here are not effective in other tissues. 

Glucocorticoids—mainly cortisol (see p. 374)—induce all of the key enzymes involved in gluconeogenesis [4, 6, 8, 9]. At the same time, they also induce enzymes involved in amino acid degradation and thereby provide precursors for gluconeogenesis. Regulation of the expression of PEP carbo Q -kinase, a key enzyme in gluconeogenesis, is discussed in detail on p. 244. 

Start with G-6-P, again note that this molecule is at a metabolic crossroads. First convert to G-l-P using Phosphoglucomutase  

This reaction is very much like PGA Mutase, requiring the bis phosphorylated intermediate to form and to regenerate the phosphorylated enzyme intermediate. Note that this reaction is easily reversible, though it favors G-6-P. 

Again a separate support enzyme, Phosphoglucokinase, is required to form the intermediate, this time using ATP as the energy source  

UDP-glucose pyrophosphorylase, which catalyzes the next reaction, has a near zeroAG° 

Finally glycogen is synthesized with Glycogen Synthase  

Overactivity of gluconeogenesis due to increased secretion of catecholamines, cortisol, or growth hormone or an increase in the glucagon/insulin ratio (Chapter 22) leads to hyperglycemia and causes many metabolic problems. 

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Gluconeogenesis, Glycogen Metabolism, and the Pentose Phosphate Pathway... 

Explain the effects of each of the following on the rates of glnconeogenesis and glycogen metabolism ... 

Rybicka, K. IC, 1996. Glycosomes—The organelles of glycogen metabolism. Tissue and Cell 28 253-265. 

Stalmans, W., Cadefau, J., Wera, S., and Bollen, M., 1997. New insight into die reguladon of liver glycogen metabolism by glucose. Biochemical Society Transactions 25 19—25. 

Woodget, J. R., 1991. A common denominator linking glycogen metabolism, nuclear oncogenes, and development. Trends in Biochemical Sciences 16 177-181. 

Bergstrom, J. Hultman, E. (1967). A study of the glycogen metabolism during exercise in man. Scand. J. Clin. Lab. Invest. 19,218-228. 

Figure 5. Glycogen metabolism and glycolysis. Dotted lines indicate sites of metabolic defects involving enzymes l-XI.

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

REGULATION OF GLYCOGEN METABOLISM IS EFFECTED BY A BALANCE IN ACTIVITIES BETWEEN GLYCOGEN SYNTHASE PHOSPHORYLASE (Figure 18-8)... 

Inherited deficiencies in specific enzymes of glycogen metabolism in both liver and muscle are the causes of glycogen storage diseases. 

Bollen M> Keppens S, Stalmans W Specific features of glycogen metabolism in the liver. Biochem J 1998 336 19. 

VITAMIN Be IS IMPORTANT IN AMINO ACID GLYCOGEN METABOLISM IN STEROID HORMONE ACTION... 

Filipe et al. (2001b) also suggested a parameter that influences the glycogen metabolism of GAOs under anaerobic condition. The parameter is described as below [4]. 

Michel Morange. Cyclic AMP is involved in glycogen metabolism - it is not really specific of memory. 

Phosphorylation Glycogen Metabolic Movements of Glycogen Fat Metabolic Movements of Fat Protein Metabolic Movements of Protein Tissue Cooperation Liver Muscle Ketone Bodies... 

H, receptors in brain slices can also stimulate glycogen metabolism [5] and can positively modulate receptor-linked stimulation of cAMP synthesis. The activation of brain cAMP synthesis by histamine is a well studied phenomenon that reveals a positive interaction between histamine receptors [35]. When studied in cell-free preparations, this response shows characteristics of H2, but not H receptors. When similar experiments are performed in brain slices, however, both receptors appear to participate in the response. Subsequent work showed that H receptors do not directly stimulate adenylyl cyclase but enhance the H2 stimulation, probably through the effects of calcium and PKC activation on sensitive adenylyl cyclase iso forms (see Ch. 21). 

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