Which enzymes are involved in the rate-limiting step of glycogenolysis?

The correct answer focuses on the enzymes that play a crucial role in the rate-limiting step of glycogenolysis, which is the process of breaking down glycogen into glucose. Glycogen phosphorylase is the main enzyme responsible for cleaving glucose units from glycogen, specifically by breaking the α-1,4-glycosidic bonds. This reaction releases glucose-1-phosphate, which can then be converted into glucose-6-phosphate for energy production or converted to free glucose, especially in the liver.

The debranching enzyme is also important in glycogenolysis, particularly when glycogen branches are encountered. It has two main activities: one to transfer a small oligosaccharide near a branch point to the end of another chain, and the other to hydrolyze the α-1,6-glycosidic bond at the branch point itself. Without the debranching enzyme, glycogen can only be broken down to a certain point because the α-1,6 linkages at branch points would prevent complete utilization of the glycogen stored.

Thus, the collaboration of glycogen phosphorylase and the debranching enzyme constitutes the rate-limiting step of glycogenolysis, as