Regulation of glycogen metabolism is tightly controlled at the level of the activity of glycogen phosphorylase. Which of the following is known to act as a negative effector of the phosphorylated (most active) form of glycogen phosphorylase?

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Quizplus · Accepted Answer

The Answer is D
EXPLANATION: Glycogen homeostasis is controlled by regulating the rate of glycogen synthesis and breakdown. Release of glucose from stored glycogen is the role of glycogen phosphorylase (generally just called phosphorylase). The rate of glucose liberation from glycogen by phosphorylase is controlled primarily by short-term phosphorylation and dephosphorylation events. When phosphorylase is phosphorylated by glycogen synthase-phosphorylase kinase (generally just called phosphorylase kinase), it is more active in releasing glucose. This phosphorylation occurs in hepatocytes when stimulation by glucagon leads to increased activity of PKA, which in turn phosphorylates, and activates, phosphorylase kinase. Active phosphorylase liberates glucose 1-phosphate from glycogen which is converted to glucose 6-phosphate. The glucose 6-phosphate is either oxidized in the glycolytic pathway or the phosphate is removed by glucose 6-phosphatase and the free glucose flows into the blood. When glucose-6-phosphate levels rise in hepatocytes, due to reduced utilization, it acts as an allosteric inhibitor of the phosphorylated and active form of phosphorylase.

Regulation of Glycogen Metabolism Is Tightly Controlled at the Level