Osteoclasts dissolve the mineral phase of bone by secreting acid across their ruffled border into the sealed resorption lacuna. Which enzyme generates the intracellular protons pumped out by the H⁺-ATPase?

• A Alkaline phosphatase
• B Tartrate-resistant acid phosphatase
• C Cathepsin K
• D Carbonic anhydrase II ✓

Explanation

Carbonic anhydrase II converts CO₂ and water to carbonic acid inside the osteoclast; the resulting protons are extruded by an H⁺-ATPase at the ruffled border while chloride follows through a chloride channel, dissolving hydroxyapatite. Cathepsin K and tartrate-resistant acid phosphatase degrade the organic matrix after demineralization but generate no protons, and alkaline phosphatase functions in mineralization.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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