Very Low Density Lipoprotein (LDL) Metabolism

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\Nascent VLDL (very Low-Density Lipoprotein) is produced in the liver, having an amphipathic shell and central core.T he central code consists of endogenous TAG i.e, non-dietary TAG. It is having apolipoproteins on the periphery. These are Apo B-100, Apo C and Apo E, the next step is the maturation of VLDL i.e. conversation of remnant VLDL in to mature VLDL.

This occurs by the donation of Apo C and Apo E by the HDL(High-Density Lipoprotein) molecule towards the nascent VLDL. This mature chylomicron now reaches the capillaries. In the capillaries, it is encountered by lipoprotein lipase enzyme which is present on the walls of capillary endothelium and activated BY Apo C-1 and Apo C 2.It convert endogenous TAG into fatty acid and glycerol.

This fatty acid is taken up by cell and this glycerol is utilized as a substrate for gluconeogenesis and hence, glucose is formed. Now because of Triacylglycerols are depleting in the core, the size of the VLDL reduces. Also, Apo C and Apo E return to HDL. Now, this VLDL is said to be VLDL remnant /IDL (intermediate density lipoprotein). 

50% of the IDL, by the help of Apo B-100, is recognized by the remnant receptors present on the hepatic cell and is taken up by liver & the other 50 %, undergoes conversion to LDL or low-density lipoprotein by the shedding of Apo E in the plasma.

The LDL molecule has high cholesterol esters in the core. Now, if the extra-hepatic cells desire cholesterol, it takes up the  LDL molecule ( by endocytosis). If the extrahepatic cells do not desire cholesterol, it is taken up by Liver

To know more how the cell takes up cholesterol click here

To see complete LDL metabolism in a step-by-step manner  click here

 

 

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