Insulin promotes hepatic glycogen storage partly through protein phosphatase-1 (PP1). What is the immediate molecular consequence of PP1 action on glycogen synthase, and how does this change enzyme activity?

• A Phosphorylation of glycogen synthase, converting it to the active a form
• B Dephosphorylation of glycogen synthase, converting it to the active a form ✓
• C Dephosphorylation of glycogen synthase, converting it to the inactive b form
• D Proteolytic cleavage of glycogen synthase into a constitutively active fragment

Explanation

Glycogen synthase is active when dephosphorylated (the a form) and inactive when phosphorylated (the b form), the opposite convention to glycogen phosphorylase. Insulin activates PP1, which removes phosphates from glycogen synthase and from phosphorylase kinase and phosphorylase a, simultaneously favoring synthesis and blocking degradation. Option A reverses the convention and would describe glucagon-driven signaling, not insulin action.

Reference: Lippincott Illustrated Reviews: Biochemistry, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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