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 ?
Results: Oxidised low density lipoprotein at 5-10 ug/mL increased tissue factor and lectin-like oxidised low density lipoprotein receptor expression, whereas 20-50 ug/mL oxidised low density lipoprotein attenuated tissue factor expression.
While increased high density lipoprotein cholesterol level was found to be associated with 36% lower risk of obesity.4 LPL gene rs328 (S447X) polymorphism is reported as gain of function by many investigators.
Hypertriglyceridemia is a complex clinical condition with an unclear association with atherosclerosis.5,6 Patient with moderate hypertriglyceridemia, will have high levels of lowdensity lipoprotein present in plasma.
The IDL lipoprotein, on the other hand, is the precursor of LDL, which is also known as "the bad" cholesterol.
CEs may be exchanged by cholesterol ester transfer protein (CETP) to triglyceride-rich lipoproteins, destined for the liver.
Hydrogenated cottonseed oil behaved the worst by raising blood triglycerides and lipoprotein levels.
Moreover, sdLDL particles contain less antioxidative vitamins and are therefore more susceptible to oxidation than larger forms of lipoproteins [62].
The exon 8 of LPL gene is the key sequence for coding the catalytic center of lipoprotein lipase (Li et al., 2014).
In fact, most of the increase in triglyceride rich lipoproteins (TRLs) observed in diabetic dyslipidemia is due to VLDL1 particles.
In addition, the rates of very low-density lipoprotein are only significant in the post test stage compared to the base stage.
HDL is the smallest of die lipoproteins. About half is lipids (25% phospholipids and 15% cholesterylester, while UC and TG both constitute 5%).