VLDL synthesised in the liver with apoprotein B100. VLDL receives apoproteins CII and E from HDL. Like chylomicrons, VLDLs travels around the circulatory system until they associate with lipoprotein lipase, an enzyme bound to the endothelial surface. This association is mediated through apoprotein CII. The lipoprotein lipase hydrolyses the triacylglycerol to liberate free fatty acids which diffuse into the local tissues. As triacylglycerol is lost, the VLDL shrinks and forms LDL. The released fatty acids can be reassembled into triacylglycerols for storage as fat or oxidised to produce ATP. The LDL return apoprotein CII and E to HDL and are taken up by receptor mediated endocytosis by the extra hepatic tissues (with some being taken back up by the liver). LDL having lost most of their triacylglycerols are rich in cholesterol and cholesterol esters and represent the route by which cholesterol is transported form the liver to the tissues (although all tissues can make cholesterol to some extent).

As VLDL particles are transported in the bloodstream, Lipoprotein Lipase catalyzes triacylglycerols removal by hydrolysis.

With removal of triacylglycerols and some proteins, the % weight that is cholesterol esters increases. VLDL are converted to IDL, and eventually to LDL.

VLDL à IDL à LDL

The lipid core of LDL is predominantly cholesterol esters. Whereas VLDL contains 5 Apoproteins types (B-100, C-I, C-II, C-III, & E), only one protein, Apoproteins B-100, is associated with the surface monolayer of LDL.

Cells take up LDL by receptor-mediated endocytosis. The cholesterol in LDL is then used by cells, e.g., for synthesis of cellular membranes.

The LDL receptor was identified by M. Brown & J. Goldstein, who were awarded the Nobel prize.

The LDL receptor is a single-pass transmembrane glycoprotein with a modular design.

Function is to transport endogenously synthesised TAG to the extra hepatic tissues where it can be stored as fat or to muscles where the constituent fatty acids can be used for energy. The cholesterol is delivered to extra hepatic tissues once VLDL has been metabolised to LDL.