Apolipoprotein

Apolipoproteins are proteins that bind to fats (lipids). They form lipoproteins, which transport dietary fats through the bloodstream. Dietary fats are digested in the intestine and carried to the liver. Fats are also synthesized in the liver itself. Fats are stored in fat cells (adipocytes). Fats are metabolized as needed for energy in the skeletal muscle, heart, and other organs and are secreted in breast milk.

The fatty, oily components of lipoproteins are not soluble in water. But because of their detergent-like (amphipathic) properties, apolipoproteins can dissolve them.

Apolipoproteins also serve as enzyme co-factors, receptor ligands, and lipid transfer carriers that regulate the metabolism of lipoproteins and their uptake in tissues.

Functions

• They are enzyme cofactors (C-|| for lipoprotein lipase and A-| for lecithin)
• Lipid transport proteins
• Ligands for interaction with lipoprotein receptors in tissues ( apoB100 for and apoE for LDL-receptors, apoA| for HDL receptors)

Classes

There are six major classes of apolipoproteins and several sub-classes:

• A (apo A-I, apo A-II, apo A-IV, and apo A-V)
• B (apo B48 and apo B100)
• C (apo C-I, apo C-II, apo C-III, and apo C-IV)
• D
• E
• H

Hundreds of genetic polymorphisms of the apolipoproteins have been described, and many of them alter their structure and function.

Synthesis and regulation

Apolipoprotein synthesis in the intestine is regulated principally by the fat content of the diet.

Apolipoprotein synthesis in the liver is controlled by a host of factors, including dietary composition, hormones (insulin, glucagon, thyroxin, estrogens, androgens), alcohol intake, and various drugs (statins, niacin,and fibric acids). Apo B is an integral apoprotein whereas the others are peripheral apoproteins.

See also

• Apoprotein

External links

• HuGENet Review
• Apolipoprotein AI Mutations and Information

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