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The formation, composition, role and metabolism of lipoproteins (LP)

LP are complexes between Proteins and different types of Lipids. Proteins of LP are named apoproteins. There are 5 groups of apoproteins. They're depicted as A, B, C, D, E. Each group is subdivided into subgroups (A1, A2 etc). There are following species of LP:

1) Very low density LP (VLDL), or pre-beta LP

2) Low density LP (LDL), or beta-LP

3) High density LP (HDL), or alfa-LP.

The differences between LP are:

1. quantitative composition and density which depends on content of proteins in LP. HDL has got 50% of Proteins; LDL – 20%; VLDL – 7%. VLDL consists of 55% of TAG; LDL contain 50% of Cholesterol

2. velocity of movement in electrical field: the fastest LP are HDL and slowest are VLDL

3. diameter: HDL are smallest and have diameter as 10-15nm; VLDL are biggest

4. function: VLDL transfer TAG and Cholesterol from liver to extrahepatic tissues. LDL transfer Cholesterol from liver to extrahepatic tissues. Hence they're named as atherogenic LP. HDL are synthesized by liver and small intestine. HDL transfer unused Cholesterol from extrahepatic tissues to liver where it is oxidized to bile acids. Hence HDL are named as antiatherogenic LP. The antiatherogenic function of HDL due to the action of enzyme Lecithine Cholesterol Acyl transferase (LHAT). It is enzyme of blood plasma. Apoproteins of HDL are activators of its.this enzyme catalyzes the reaction of Cholesterol esters formation: Cholesterol + Lecithine = Cholesterol esters + Lysolecithine. Cholesterol esters is insoluble compound and sinks in nucleus of HDL. The ratio LDL/HDL is determined in blood plasma, which is equal 3. This ratio is named atherogenic index. Increase of its shows the risk of atherosclerosis.

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