Epinephrine acting on skeletal muscle activates glycogenolysis through a signaling cascade. After protein kinase A phosphorylates phosphorylase kinase, an additional second messenger independently boosts phosphorylase kinase activity during muscle contraction. What is this additional activator?

• A Inositol triphosphate generated from phosphatidylinositol turnover
• B Calcium-calmodulin complex released from the sarcoplasmic reticulum ✓
• C Fructose-2,6-bisphosphate rising in the myocyte
• D AMP-dependent activation independent of phosphorylation state

Explanation

Phosphorylase kinase is a multimeric enzyme containing calmodulin as a delta subunit. It is activated both by PKA-mediated phosphorylation and directly by calcium released from the sarcoplasmic reticulum during contraction, coupling glycogen breakdown to mechanical work. Option D describes AMP activation of muscle glycogen phosphorylase b itself, which is a separate mechanism acting downstream on the phosphorylase, not on phosphorylase kinase.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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