Glycogen metabolism regulatory mechanisms

The flow of intermediates through metabolic pathways is controlled by 1bir mechanisms 1) the availability of substrates 2) allosteric activation and inhibition of enzymes 3) covalent modification of enzymes and 4) induction-repression of enzyme synthesis. This scheme may at first seem unnecessarily redundant however, each mechanism operates on a different timescale (Figure 24.1), and allows the body to adapt to a wde variety of physiologic situations. In the fed state, these regulatory mechanisms ensure that available nutrients are captured as glycogen, triacylglycerol, and protein. 

Glycogen metabolism in liver is regulated by phosphorylation and dephosphorylation of regulatory and metabolic enzymes. Control of the phosphorylation state is mediated by Ca " ", cAMP, cytosolic glucose concentration, and perhaps, in the case of insulin, by another mechanism. 

Mechanisms. cAMP plays a central role as a second messenger in the regulation of cell metabolism (14). Binding of cAMP with the regulatory subunit of a protein kinase initiates a cascade of enzymatic reactions that ultimately lead to the breakdown of glycogen and release of glucose to the blood stream. The intracellular concentration of cAMP represents a balance between the action of adenylate cyclase (which produces cAMP... 

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