Skeletal muscle glycogen

Skeletal muscle glycogen delivers glucose primarily as a response to contractile stress. Regulation occurs through both modification of the enzyme phosphorylase, primarily by the action of epinephrine-adrenaline and allosteric regulation of phosphorylase related to a demand for ATP. 

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. 

Additional information <1> (<1> isozyme of calmodulin-dependent multifunctional protein kinase II in smooth-muscle [5] <1> caldesmon is not a substrate of smooth-muscle myosin light-chain kinase [3] <1> no substrates are bovine cardiac C-protein, bovine brain fodrin, rabbit skeletal muscle glycogen synthase, phosphorylase B, troponon (I -I- T -I- C), actin, tropomyosin, smooth-muscle actin, filamin, vinculin, cr-actinin, protamine or phosvitin [1]) [1-3]... 

Groop L. The effect of (steroid) immunosuppression on skeletal muscle glycogen metabolism in patients after kid- 292. ney transplantation. Transplantation 1996 61(6) 889-93. 

Pitcher, J., Smythe, C., Campbell, D. G., and Cohen, P. 1987. Identification of the 38-kDa subunit of rabbit skeletal muscle glycogen synthase as gtycogenin. Eur. J. Biochem. 169,497-502. 

As noted previously, like skeletal muscle, glycogen depletion in liver during endurance exercise is much less in trained animals and in animals who have had free fatty acids artificially elevated. No evidence exists that the mechanism proposed by Randle to account for the inhibition of carbohydrate metabolism in muscle by oxidation of fatty acids is operative in the liver. Thus other factors must be responsible for the slower rate of liver glycogen depletion in these situations. Such factors may include a smaller increase in catecholamine levels, a smaller reduction in insulin levels, and a smaller reduction in blood flow to the liver during exercise (19,20). 

About 80% of the total body vitamin Bg is in skeletal muscle glycogen phos-phorylase, with a relatively slow turnover. Based on longer term tracer studies, Coburn (1990, 1996) has suggested a total body pool of 250 mg, or 15 nmol (3.7 /xg) per g of body weight, with a loss of about 0.13% per day, hence a... 

The metabolism of skeletal-muscle glycogen is unaffected because of the inability of acarbose to be absorbed (see below) (Calder and Geddes, 1989). 

Mechanism of Stimulation of Mammalian Skeletal Muscle Glycogen Synthesis... 

As seen in T able 14, there are two phosphorylation sites at the N-terminal region of the rabbit skeletal muscle glycogen synthase. The remaining seven are situated at the C-terminal region. The cAMP-dependent protein kinase preferentially phosphorylates three sites, la, lb, and 2. The cAMP-dependent kinase can also phosphoryiate sites 3a and 4 but at a much slower rate and thus is not considered to be as important as glycogen synthase kinase 3 for those sites. There are overlapping specificities among the different protein kinases for site 2 as phosphorylase kinase, calmodulin-dependent protein kinase and protein kinase C also can phosphoryiate this site. ... 

Glycogen is stored in the liver and skeletal muscle. Glycogen s)mthesis and degradation in the liver are carefully regulated. As we will see in Section 21.7, these two processes are intimately involved in keeping blood glucose levels constant. 

Skeletal muscle Glycogen Fatty acids None... 

What would happen to a 70-kg man if the 135,000 kcal stored as triacylglycerols in his 18 kg of adipose tissue were stored instead as skeletal muscle glycogen It would take approximately 34 kg glycogen to store as many calories. Glycogen, because it is a polar molecule with -OH groups, binds approximately 4 times its weight in water, or 136 kg. Thus, his fuel stores would weigh 170 kg. 

The regulation of glycogenolysis in skeletal muscle is related to the availability of ATP for muscular contraction. Skeletal muscle glycogen produces glucose... 

Beynon, R. J., Fairhurst, D.. and Cookson, E. J. (1986). Turnover of skeletal muscle glycogen phosphorylase. Biomed. Biochim. Acta 45,1619-1625. 

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