| Enzymes and transfer proteins
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| Two hydrolases, lipoprotein lipase (LPL) and hepatic triglyceride lipase (HTGL), remove triacylglycerols from triacylglycerol - rich lipoprotein particles. LPL binds to
heparan sulfate proteoglycans on the surface of the vascular endothelial cells, and HTGL is associated with liver plasma membranes. LPL digests triacylglycerols in chylomicrons and VLDL, and releases fatty acids and glycerol for cell metabolism or storage. LPL may hydrolyze as much as 10 g triacylglycerol per hour. HTGL acts on particles already partially digested by LPL: it facilitates conversion of IDL into LDL.
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| Lecithin:cholesterol acyltransferase (LCAT) is a glycoprotein enzyme associated with HDL. LCAT esterifies cholesterol acquired by HDL. LCAT is activated by apoAI. Note that inside cells cholesterol is esterified by a different enzyme, acylCoA:acylcholesterol transferase (ACAT).
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| Cholesterol ester transfer protein (CETP) facilitates the transfer of cholesterol esters from HDL to triacylglycerol-rich lipoproteins in exchange for some of their triacylglycerols and apoproteins. CETP is synthesized in the liver.
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