Lipoproteins


Also found in: Dictionary, Thesaurus, Medical, Wikipedia.

Lipoproteins

 

complexes of proteins and lipids. Lipoproteins occur in plants and animals as constituents of all biological membranes and lamellar structures (in the myelin sheath of nerves, in the chloroplasts of plants, in the receptor cells of the retina). They occur in free form in blood plasma, from which they were first isolated in 1929.

Lipoproteins are classified according to chemical structure and lipid-protein ratio. They are subdivided into four main classes according to sedimentation rate during centrifugal separation: (1) high-density lipoproteins (52 percent protein and 48 percent lipids, primarily phospholipids), (2) low-density lipoproteins (21 percent protein and 79 percent lipids, mainly cholesterol), (3) very low-density lipoproteins (9 percent protein and 91 percent lipids, mostly triglycerides), and (4) chylomicrons (1 percent protein and 99 percent triglycerides).

It is thought that lipoprotein structure is micellar (the protein bonded to the lipid-cholesterol complex owing to hydrophobic interaction) or analogous to that of molecular compounds of proteins and lipids (the phospholipid molecules located in flexures of the polypeptide chains of protein subunits). The study of lipoproteins is complicated by the instability of lipid-protein complexes and by difficulties encountered in their isolation in natural form.

REFERENCE

Finean, J. Biologicheskie ul’trastruktury. Moscow, 1970. (Translated from English.)

N. V. PROKAZOVA

References in periodicals archive ?
But are there any studies that show a relationship between lipoproteins HDL, LDL and COPD?
High density lipoprotein (HDL) takes cholesterol away from the cells and back to the liver, where it is either broken down, or is passed from the body as a waste product.
Also, tables listing age-specific cut points for abnormal lipoprotein concentrations were developed.
Lipoprotein lipase removes triglycerides from VLDLs so that the triglycerides can be used or stored.
Although we did not try to answer the question in our original article, it is possible that the difference (44 mg/dL) between the calculated low-density lipoprotein cholesterol (LDL-C; 172 mg/dL) and the directly measured LDL-C (128 mg/dL) lies in (1) the use of triglycerides (TG) divided by 5 in the Friedewald formula and (2) the cholesterol of other lipoprotein fractions, such as intermediate-density lipoprotein cholesterol (IDL-C), Lp(a) (lipoprotein(a)), apo E-rich high-density lipoprotein cholesterol, etc, that may not be measured, partially or fully, by the homogeneous LDL-C assay.
Change in lipoproteins cause atherosclerosis, damage to endothelium and other heart diseases.
Association of levels of lipoprotein Lp(a), plasma lipids, and other lipoproteins with coronary artery disease documented by angiography," Circulation, vol.
Tokfrey et al [9] believe that the fact that the natural levels of lipoproteins stay the same is due to the daily body activities in adults and children.
The liver and intestine secrete apoAi that may initiate particle formation, which may also result from lipolysis of TG-rich lipoproteins [4] when apoAi and the relative excess of phospholipids pinch off from the lipoprotein.
Plasma triglycerides are predominantly present in 2 types of lipoproteins namely the chylomicrons and VLDL.
Lipoproteins are small particles in the blood stream that consist of protein, cholesterol, triglycerides, and phospholipids, and they are primarily formed in the liver.
High density (HDL) and low density (LDL) lipoproteins carry