A healthy 25-year-old man participates in a clinical study to determine glycogen stores after an 8-hour overnight fast. In preparation for the study, he follows a high-carbohydrate diet for 3 days. In the morning, he receives an injection of glucagon, which results in a significant increase in his serum glucose concentration. Which of the following best describes a reaction that would occur during the breakdown of hepatic glycogen to glucose in this patient?

Question

Quizplus · Accepted Answer

During glucagon-stimulated glycogen breakdown, phosphorylase is activated and glucose present in α-1,4-glycosidic linkages is phosphorylytically released. Phosphorylase cannot remove glucose residues from the branch points (α-1,6 linkages) in glycogen. The activity of phosphorylase ceases 4 glucose residues from the branch point. The removal of these branch point glucose residues requires the action of debranching enzyme, which contains 2 activities: glucotransferase and glucosidase. The transferase activity removes the terminal 3 glucose residues of one branch and attaches them to a free C-4 end of a second branch. The glucose in α-(1,6)-linkage at the branch is then removed by the action of the glucosidase activity.

A Healthy 25-Year-Old Man Participates in a Clinical Study to Determine