A cell-free, glycogen-free, UTP-free homogenate of a mutant liver cell line is m

Question

A cell-free, glycogen-free, UTP-free homogenate of a mutant liver cell line is made.

A. Addition of cAMP causes an elevation in the rate of degregation of radioactively labeled glycogen added in trace amounts.

B. If cAMP phosphodiesterase (cAMP-5' AMP) is added, breakdown of labeled glycogen continues unabated. If under the same conditions UDP-glucose plus an oligosaccharide acceptor is added instead of labedl glycogen, little if any labeled glycogen is made.

C. If to the homogenate in B is added 1.0 mM glucose-1-P, sunthesis of labeled glycogen from glucose readily occurs after a short period of time.

What is a possible site or sites of the mutation? Explain the observations listed above.

Explanation / Answer

When harmone glucagoan/epinepherin bind to receptor, it activate adenyl cyclase which produce cAMP . cAMP activate protein kinase A which further activatate glycogen phosphorylase that involve in breakdown of glycogen. cAMP phosphodiesterase degrade cAMP means cause inhibition of glycogen breakdown .

Mutation in cAMP phosphodiesterase inhibit its action on cAMP and glycogen breakdown continue occur. Mutation in phosphoglucomutase inhibit conversion of glucose 1 P to glucose 6P. Glucose -1-P accumulation inhibit activity of glycogen phosphorylase and activation of glycogen synthase. Therefore, synthesis of glycogen occur after a short period of time.

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