Reverse cholesterol transport (RCT) is the mechanism by which peripheral cholesterol is returned to the liver. Which enzyme esterifies cholesterol on HDL during RCT, and what is its significance?

• A LCAT (lecithin-cholesterol acyltransferase) — transfers acyl group from lecithin to cholesterol, creating cholesterol esters that enter HDL core, driving cholesterol absorption into HDL ✓
• B CETP (cholesterol ester transfer protein) — adds cholesterol esters directly to HDL
• C ACAT (acyl-CoA cholesterol acyltransferase) — esterifies cholesterol in HDL surface
• D Hormone-sensitive lipase — hydrolyzes HDL cholesterol esters

Explanation

LCAT (activated by ApoA-I on nascent HDL) transfers the sn-2 fatty acid from phosphatidylcholine (lecithin) to the 3-hydroxyl group of free cholesterol on the HDL surface, forming cholesterol esters and lyso-PC. Cholesterol esters migrate into the hydrophobic HDL core, maintaining low free cholesterol concentration on the surface, creating a gradient for continued passive cholesterol efflux from peripheral cells. This process converts nascent (discoidal) HDL to mature spherical HDL3→HDL2. CETP then transfers cholesterol esters from HDL to VLDL/LDL in exchange for triglycerides.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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