In smooth muscle, calcium binding to calmodulin activates myosin light chain kinase (MLCK). What is the mechanism by which the calcium-calmodulin complex activates MLCK?

• A Causes dimerization of MLCK
• B Translocates MLCK to the plasma membrane
• C Phosphorylates MLCK at a regulatory site
• D Removes an autoinhibitory domain from MLCK ✓

Explanation

MLCK is maintained inactive by an autoinhibitory domain that blocks the catalytic site. When Ca2+-calmodulin binds to MLCK, it displaces this autoinhibitory domain, allowing the kinase to phosphorylate myosin light chains and initiate contraction. This is direct allosteric activation, not phosphorylation or dimerization.

Reference: Lehninger Principles of Biochemistry, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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