Which statement is true of glycogen phosphorylase?

• A. It catalyzes the phosphorolytic cleavage of \(ext{α}(1 ightarrow 4)\) glycosidic bonds in glycogen.
• B. It requires ATP as a cofactor for its catalytic activity.
• C. It removes glucose residues from the non-reducing ends by hydrolysis.
• D. It is activated by insulin in liver cells.

Answer: (A)

Verified step by step guidance

1. Step 1: Understand the role of glycogen phosphorylase. Glycogen phosphorylase is an enzyme involved in glycogen metabolism. It catalyzes the breakdown of glycogen into glucose-1-phosphate by cleaving \(\text{α}(1 \rightarrow 4)\) glycosidic bonds.
2. Step 2: Analyze the mechanism of action. Glycogen phosphorylase performs phosphorolysis, not hydrolysis, meaning it uses inorganic phosphate (Pi) to cleave the glycosidic bond, producing glucose-1-phosphate instead of free glucose.
3. Step 3: Evaluate the requirement for ATP. Glycogen phosphorylase does not require ATP as a cofactor for its catalytic activity. Instead, it uses inorganic phosphate (Pi) directly in the reaction.
4. Step 4: Examine the regulation by insulin. Insulin generally promotes glycogen synthesis rather than glycogen breakdown. Glycogen phosphorylase is inhibited by insulin in liver cells, not activated.
5. Step 5: Confirm the correct statement. Based on the above analysis, the correct statement is that glycogen phosphorylase catalyzes the phosphorolytic cleavage of \(\text{α}(1 \rightarrow 4)\) glycosidic bonds in glycogen.