A lipoprotein is a biochemical assembly that contains both proteins and lipids and may be structural or catalytic in function. Lipoproteins may be enzymes, proton pumps, ion pumps, or some combination of these functions. Examples include the high density and low density lipoproteins of the blood and the transmembrane proteins of the mitochondrion and the chloroplast.
The lipids are often an essential part of the complex, even if they seem to have no catalytic activity themselves. To isolate transmembrane lipoproteins from their associated membranes, detergents are often needed.
Lipoproteins of the body are necessary to carry insoluble fats around the body.
- Chylomicrons - carry triacylglycerol (fat) from the intestines to adipose tissue.
- Very low density lipoproteins - carry (newly synthesised) triacylglycerol from the liver to adipose tissue.
- Intermediate density lipoproteins - this lipoprotein is the intermediate between VLDL and LDL. It is not normally detectable in the body.
- Low density lipoproteins - carry cholesterol from the liver to cells of the body. Known as the "bad cholesterol" lipoprotein.
- High density lipoproteins - collects cholesterol from the body's tissues, and brings it back to the liver.