Metabolism of Lipids 9 Sections27 LessonsLifetime
VLDL (Very Low Density Lipoproteins)
When fatty acids are in surplus amount (more than our body’s needs), they are converted into fats by combining with glycerol in the liver.
Surplus carbohydrates are also converted into fats.
These fats are in the form of VLDL.
VLDL are smaller in size than chylomicrons and synthesized in liver.
Cholesterol in VLDL is unesterified and have Protein ApoB-100.
From liver they come into the circulation and epithelial cells of muscles and adipose tissue.
They are again acted upon by Lipoprotein lipase and fatty acids are removed.
In the circulation they also take up ApoC-II and ApoE from HDL.
ApoC-II activates the enzyme lipoprotein lipase and 3 FA and glycerol are formed.
Intermediate Density Lipoproteins (IDL)
VLDL remnants are also known as IDL.
About 70% of LDL remnants (IDL) go to the liver.
They return ApoC II and ApoE to HDL while ApoB-100 is retained.
Receptors of ApoB-100 are in liver – endocytosis – lysosomes – degradation.
IDL give their fatty acid to HDL. There is exchange (IDL give fatty acid to HDL and HDL gives Cholesterol ester to IDL by LCAT enzyme).
With further loss of Fatty acid it is converted to LDL and goes to extrahepatic tissues.
LDL are rich in Cholesterol ester (CE), Free Cholesterol (FC), Phospholipids (PL) and small amount of TAGs (45% cholesterol) and ApoB-100.
IDL cannot be measured in the blood as it is formed temporarily & is immediately taken up by the liver or converted into LDL.