Submitted by Thiruvelan on Thu, 06/24/2010

Blood is watery, and cholesterol is fatty; these two do not mix. Cholesterol transportation in the bloodstream needs to carry in small packages called lipoproteins. This package contains fats in the center and surrounded by proteins outside.

What are apolipoprotein and lipoprotein?

Lipoproteins have a lipid core and protein cover. The lipids part consists of cholesterol esters (CE) and triglycerides (TG). The outer cover consists of proteins (apolipoprotein). Lipoproteins transport triglycerides and cholesterol from the liver and gut. It delivers to the periphery muscles and adipocytes. Where they use triglycerides and cholesterol for energy, cellular maintenance, and steroid creation.

Apolipoprotein is the protein; it forms lipoproteins by binding with hydrophobic (water fearing) lipids.

Apolipoproteins do several important works; structural integrity, solubility, and cofactors in enzymatic reactions. Additionally, it helps interacting lipoproteins with a receptor on a cell. Throughout the body, cells have protein receptors to attach to their outer surface.

Based on the density, there are five classes of lipoproteins (from high to low); they are:

  1. High-density lipoprotein (HDL),
  2. Low-density lipoprotein (LDL),
  3. Intermediate density lipoprotein (IDL),
  4. Very-low-density lipoprotein (VLDL), and
  5. Chylomicron.

There are two important classes of apolipoproteins; they are:

  • Apolipoprotein A-I (apoA1) is an alpha mobility; be in high-density lipoproteins (HDL). There are more than one apoA1 per HDL particle.
  • Apolipoprotein B (apoB) is a beta mobility; mostly be in low-density lipoprotein (LDL). There is only one apoB per LDL particle.

Lipoprotein classifications

Lipoproteins of large size have low density (contain more fat and less protein). Whereas, lipoproteins of small size are high density with less fat and more protein.

  • Chylomicron transport triglyceride (fat) from intestines to liver, skeletal muscle, and adipose tissue. 99% of its total weight contains lipid.
  • VLDL - Very low-density lipoproteins transport triglycerides from the liver to adipose tissue. 91% of its total weight contains lipid.
  • IDL - Intermediate density lipoproteins are not usually detectable in the blood. Its size is between VLDL and LDL. 91% of its total weight contain lipid.
  • LDL – Low-density lipoproteins transports cholesterol from the liver to cells. 80% of its total weight contain lipid.
  • HDL – High-density lipoproteins brings back cholesterol from the body tissues to the liver. 44% of its total weight contains lipid.

Each lipoprotein has a varying proportion of triglycerides (TG) and cholesterol ester (CE). Once cells consume lipids in the lipoprotein; the triglyceride level drops and protein raises.