Intracellular glycogen

Insulin is a storage hormone produced by the pancreas. Insulin shuttles nutrients, such as carbohydrates, fats and amino acids (derived from proteins) into cells. The main function of insulin is to maintain homeostasis of circulatory glucose, and intracellular glycogen storage. It also aids in fat storage. 

The liver uses two mechanisms for endogenous glucose production, the mobilization of intracellular glycogen (glycogenolysis) and the synthesis of glucose from noncarbohydrate precursors (gluconeogenesis). 

Figure 2.5 Effect of yeast storage temperature on intracellular glycogen concentration.

The reason why mnltiple yeast generations can have a negative effect on a culture s fermentation performance is nnclear. However, multiple generations will result in reduced levels of intracellular glycogen and an increase in trehalose, indicating additional stress conditions as the cycles progress (Table 2.3) (Boulton Qnain, 2001). 

Striated muscle is composed of multinucleated muscle fiber cells surrounded by an electrically excitable plasma membrane, the sarcolemma. An individual muscle fiber cell, which may extend the entire length of the muscle, contains a bundle of many myofibrils arranged in parallel, embedded in intracellular fluid termed sarcoplasm. Within this fluid is contained glycogen, the high-energy compounds ATP and phosphocreatine, and the enzymes of glycolysis. 

Potassium is the second most abundant cation in the body and is found primarily in the intracellular fluid. Potassium has many important physiologic functions, including regulation of cell membrane electrical action potential (especially in the myocardium), muscular function, cellular metabolism, and glycogen and protein synthesis. Potassium in PN can be provided as chloride, acetate, and phosphate salts. One millimole of potassium phosphate provides 1.47 mEq of elemental potassium. Generally, the concentration of potassium in peripheral PN (PPN) admixtures should not exceed 80 mEq/L (80 mmol/L). While it is safer to also stick to the 80 mEq/L (80 mmol/L) limit for administration through a central vein, the maximum recommended potassium concentration for infusion via a central vein is 150 mEq/L (150 mmol/L).14 Patients with abnormal potassium losses (e.g., loop or thiazide diuretic therapy) may have higher requirements, and patients with renal failure may require potassium restriction. 

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... 

Glycogen and its enzymes are compartmentalized. Glycogen granules are only present in astrocytes of adult animals but are found in both astrocytes and neurons of immature animals. Of the enzymes involved in glycogen metabolism, glycogen phosphorylase is found in astrocytes only. Under steady-state conditions, it is probable that less than 10% of phosphorylase in brain is in the unphosphorylated b form (requiring AMP). This form is probably not very active at the low AMP concentrations present when intracellular glucose is sufficient to maintain ATP synthesis. Brain phosphorylase b kinase is activated indirectly by cAMP and by the molar concentrations... 

A crucial kinase that functions as an intermediary in numerous intracellular signaling pathways is the enzyme glycogen synthase kinase-3 (GSK-3) 898... 

All muscle types require ATP to achieve contraction. Glucose, fatty acids and amino acids may all be used as oxidizable substrates to produce ATP and all three energy sources may be obtained from stored intracellular sources (glycogen, triglyceride and protein) or imported from the blood stream. In quantitative terms, skeletal muscle is... 

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