Lipoproteins

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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 ?
Divided into three main parts, High-Density Lipoproteins first examines normal HDL particles, then describes defective HDL, and finally addresses the therapeutic normalization of subnormal levels and defective biological activities of this lipoprotein class.
Homogeneous assay for direct determination of high-density lipoprotein cholesterol evaluated.
Yet the study provides another reason for men to improve the concentrations of high-density lipoproteins (HDL) in their blood.
High-density lipoproteins (HDL) -- the good guys -- ferried cholesterol away from artery walls to the liver for disposal, while low-density lipoproteins (LDL) deposited lipids, which could clog arteries.
Women who took estrogen alone or estrogen plus progestin had higher blood concentrations of high-density lipoproteins (HDL), molecules that help remove cholesterol from the body and play a role in preventing heart disease.
For example, an Environmental Protection Agency study showed that drinking highly chlorinated water "subtly but noticeably shifted" a mouse's transport of cholesterol from high-density lipoproteins (the "good" lipoproteins) in the blood to the "bad" low-density lipoproteins, which foster atherosclerosis (SN: 6/3/89, p.
A new study shows that regular hour-long strolls -- which do little to improve cardiovascular fitness -- can nevertheless reduce a woman's heart disease risk by boosting her blood levels of high-density lipoproteins (HDLs), which help remove cholesterol from the body.
Compared with saturated fat, trans fat sparked a greater increase in LDL-carried cholesterol and a greater reduction in high-density lipoproteins (HDLs), the so-called "good" lipoproteins.
Consuming monounsaturates doesn't raise serum cholesterol levels, as saturated fats can, nor tend to lower levels of high-density lipoproteins (HDLs)--believed responsible for clearing cholesterol from the blood -- as can fats high in polyunsaturates, such as corn oil.
Scientists think high-density lipoproteins help remove cholesterol from the blood.
In women and men, chlorinated drinking water was also linked to comparable increases in low-density lipoproteins -- the so-called "bad" lipoproteins that carry cholesterol into the bloodstream -- but without any changes in the "good" high-density lipoproteins that remove cholesterol from blood.

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