The cleavage of glycogen by glycogen phosphorylase releases which of the following products?

• A. Free glucose
• B. Glucose-6-phosphate
• C. Glucose-1-phosphate
• D. UDP-glucose

Answer: (C)

Verified step by step guidance

1. Understand the role of glycogen phosphorylase: Glycogen phosphorylase is an enzyme that catalyzes the phosphorolytic cleavage of glycogen to release glucose residues. This process involves breaking α-1,4 glycosidic bonds in glycogen.
2. Recognize the product of glycogen phosphorylase activity: The enzyme adds inorganic phosphate (Pi) to the terminal glucose residue of glycogen, producing glucose-1-phosphate. This is a key intermediate in glycogen metabolism.
3. Clarify why free glucose is not the product: Free glucose is released during glycogen breakdown by a different enzyme, such as debranching enzyme, which acts on α-1,6 glycosidic bonds at branch points. Glycogen phosphorylase does not produce free glucose directly.
4. Explain why glucose-6-phosphate is not the product: Glucose-6-phosphate is formed later in the pathway when glucose-1-phosphate is converted by the enzyme phosphoglucomutase. Glycogen phosphorylase does not directly produce glucose-6-phosphate.
5. Discuss why UDP-glucose is not the product: UDP-glucose is involved in glycogen synthesis, not glycogen breakdown. It is formed during the activation of glucose-1-phosphate by UDP-glucose pyrophosphorylase in the synthesis pathway.