Chylomicrons are assembled in the intestinal mucosa and carry triacylglycerols (TAGs), cholesterol, cholesteryl esters, and fat soluble vitamins to the peripheral tissues. Chylomicrons are large, low-density particles containing mostly lipids.
Apolipoproteins on the chylomicron surface help both in targeting the chylomicron to appropriate receptors and in stimulating enzymatic activity. Chylomicrons contain a unique apolipoprotein,
, which serves as a kind of building block for chylomicron assembly. It is loaded with lipid prior to a transition from the ER to the Golgi, where the nascent chylomicron is packaged in secretory vesicles for transport to the plasma membrane.
Upon release into the plasma, the nascent chylomicron receives Apo E and Apo C-II apolipoproteins. Apo C-II is necessary for
. As the chylomicron circulates, the TAGs in the core are degraded; once ~90% have been degraded, the chylomicron is now greatly reduced in size, and its density greatly increased. At this point, the chylomicron becomes a(n)
. As this occurs,
is transferred to HDL. The particle then binds to hepatic receptors where it is endocytosed and fused with a lysosome. Everything except the receptor (which is recycled) undergoes hydrolytic degradation.