Biosynthesis of Glycogen

Figure 18-3. The biosynthesis of glycogen. The mechanism of branching as revealed by adding "C-labeled glucose to the diet in the living animal and examining the liver glycogen at further intervals.

Biosynthesis of glycogen requires dephosphorylated (active) glycogen synthase and an enzyme that creates branch points in the growing glycogen molecule, glucosyl-4,6-transferase. 

Vitamin A performs numenius biochemical functions. It promotes the production nf mucus by the basal cells of the epithelium, whereas in its absence keratin can be fonned. Vitamin A performs a function in the biosynthesis of glycogen and some steroids, and increased quantities nf coen/yme Q are found in the livers nf vitamin-deficicnt rats. Significantly. the best-known action of vitamin A is its function in the chemistry of vision. 

He received the Nobel Prize in chemistry in 1970 for his discovery of sugar nucleotides and their role in the biosynthesis of carbohydrates. Leloir had elucidated the biosynthesis of glycogen, the chief sugar reserve in animals and many microorganisms. 

Pyrimidine nucleotides, in common with purine nucleotides, are required for the synthesis of DNA and RNA. They also participate in intermediary metabolism. For example, pyrimidine nucleotides are involved in the biosynthesis of glycogen (Chapter 15) and of phospholipids... 

UDP-glucose. the glucose donor in the biosynthesis of glycogen, is an activated/or m of glucose, just as ATP and acetyl Co A are activated forms of orthophosphate and acetate, respectively. The C-1 carbon atom of theglu-cosyl unit of UDP-glucose is activated because its hydroxyl group is esteri-fied to the diphosphate moiety of UDP. 

Glycogen synthetase, the enzyme involved in the biosynthesis of glycogen, may... 

The biosynthesis of glycogen occurs from glucose-6-phosphate. As indicated earlier, this is one of several alternative fates of glucose-6-phosphate in addition to glycolysis. Glucose-6-phosphate via phosphoglucomutase and glucose-1,6-bisphosphate can be reversibly... 

If insulin acted on hexokinase, one might expect that the biosynthesis of glycogen through pathways that bypass the hexokinase reaction would not be impaired in alloxan-diabetic rats and would not be influenced by insulin. Hastings and his associates [131] observed this when they compared the biosynthesis... 

Recent pharmacological studies have shown that Radix Astragali can inhibit the biosynthesis of glycogen and dilate coronary as well as renal vessels. It also serves as a cardiac tonic, diuretic and antibacterial agent. More interestingly, it possesses an antiinfluenza action and may prevent respiratory infections. Both effects are believed to be related to the enhancement of immunological functions. 

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