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(lĭp'əprō`tēn), any organic compound that is composed of both proteinprotein,
any of the group of highly complex organic compounds found in all living cells and comprising the most abundant class of all biological molecules. Protein comprises approximately 50% of cellular dry weight.
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 and the various fatty substances classed as lipidslipids,
a broad class of organic products found in living systems. Most are insoluble in water but soluble in nonpolar solvents. The definition excludes the mineral oils and other petroleum products obtained from fossil material.
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, including fatty acidsfatty acid,
any of the organic carboxylic acids present in fats and oils as esters of glycerol. Molecular weights of fatty acids vary over a wide range. The carbon skeleton of any fatty acid is unbranched. Some fatty acids are saturated, i.e.
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 and steroidssteroids,
class of lipids having a particular molecular ring structure called the cyclopentanoperhydro-phenanthrene ring system. Steroids differ from one another in the structure of various side chains and additional rings. Steroids are common in both plants and animals.
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 such as cholesterolcholesterol
, fatty lipid found in the body tissues and blood plasma of vertebrates; it is only sparingly soluble in water, but much more soluble in some organic solvents. A steroid, cholesterol can be found in large concentrations in the brain, spinal cord, and liver.
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. The lipoprotein complex of proteins and steroids is usually provided by a weak, noncovalent interaction; proteins complexed with some other lipids do so by the information of covalent chemical bonds. There are several types of lipoproteins present in human blood, including low-density lipoproteins (LDLs)—molecules with a larger molecular weight and a relatively low percentage of protein—and high-density lipoproteins (HDLs)—molecules with a smaller molecular weight and a relatively high percentage of protein. LDLs are the main transport for cholesterol through the body. HDLs appear to carry excess cholesterol to the liver for processing. Studies have found that high levels of HDLs, which seem to retard or even reverse the formation of cholesterol plaque in the arteries (see arteriosclerosisarteriosclerosis
, general term for a condition characterized by thickening, hardening, and loss of elasticity of the walls of the blood vessels. These changes are frequently accompanied by accumulations inside the vessel walls of lipids, e.g.
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), reduce the risk of cardiovascular disease. Cell membranes are essentially lipoprotein in nature; the membrane is a continuous sheet of lipid molecules, largely phospholipidsphospholipid
, lipid that in its simplest form is composed of glycerol bonded to two fatty acids and a phosphate group. The resulting compound called phosphatidic acid contains a region (the fatty acid component) that is fat-soluble along with a region (the charged phosphate
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, in close association with proteins that either face one side of the membrane or penetrate all the way through the membrane.


Classes of conjugated proteins consisting of a protein combined with a lipid. The normal functioning of higher organisms requires movement of insoluble lipids, such as cholesterol, steroid hormones, bile, and triglycerides, between tissues. To accomplish this movement, lipids are incorporated into macromolecular complexes called lipoproteins.

All major types of lipoproteins share a general structure. The core of these spherical particles contains primarily cholesteryl ester and triglyceride. These insoluble molecules are surrounded by a coating of proteins and phospholipids that are amphipathic; that is, they have both polar and nonpolar regions. Lipoproteins vary by size and density. The largest lipoproteins, chylomicrons, are up to 500 nanometers in diameter, and since they contain primarily triglyceride they are so buoyant that they float in plasma. Very low density lipoproteins (VLDL) also primarily transport triglyceride. Low-density lipoproteins (LDL) and the smallest, most dense lipoproteins, high-density lipoproteins (HDL), transport cholesterol. The interactions of these particles with cell surface receptors and with metabolic enzymes are mediated by the protein components of the particles, termed apolipoproteins. See Cholesterol, Triglyceride

Chylomicrons contain triglyceride (fat) from the diet. In addition, they carry fat-soluble vitamins, such as vitamin A and E, into the circulation. Chylomicrons are produced in the intestine, enter the body via the lymphatic system, and then enter the bloodstream.

Very low density lipoproteins are made in the liver and contain triglyceride that is synthesized either from excess carbohydrate sources of calories or from fatty acids that enter the liver and are reassembled into triglyceride. Lipoprotein lipase (LpL) is an enzyme found on the surface of blood vessels that is responsible for the breakdown of triglyceride in lipoproteins. The partially degraded lipoproteins are termed remnants. They are ultimately removed from the circulation by the liver.

Low-density lipoproteins result after triglyceride is removed from very low density lipoproteins. This leaves a smaller, denser particle that primarily contains cholesteryl ester as its core lipid and a single protein called apoB. Cells throughout the body contain an LDL receptor that recognizes apoB. This allows the uptake of low-density lipoproteins into cells, supplying them with cholesterol. When sufficient low-density lipoproteins and cholesterol are available, cells use them in preference to synthesizing new cholesterol from precursors. In contrast, high-density lipoproteins both deliver and remove cholesterol from tissues.

Blood levels of lipoproteins are major factors regulating risk for development of coronary artery atherosclerosis. Via unknown mechanisms, low-density lipoproteins and remnant lipoproteins infiltrate and then become attached to extracellular matrix molecules within the artery. Some of the lipoproteins are internalized by macrophages and smooth muscle cells. This might first require chemical modification such as oxidation of the lipids. The resulting pathological findings are deposition of cholesterol in cells and matrix within the vessel wall, leading to a decrease in the diameter of the artery.

In contrast, high-density lipoproteins appear to prevent atherosclerosis formation. The reasons are not entirely understood. Most likely, high-density lipoproteins remove excess cholesterol that accumulates in the artery, or prevent the oxidation of low-density lipoproteins. See Arteriosclerosis


Any of a class of conjugated proteins consisting of a protein combined with a lipid.
References in periodicals archive ?
Hypoxia-inducible factor-1 (HIF-1) promotes LDL and VLDL uptake through inducing VLDLR under hypoxia.
However, castration have not significantly affect hepatic lipid metabolism, including TG synthesis, FA oxidation, and VLDL secretion.
Hydrocortisone (single dose) administered to rabbits with atherosclerosis raised TG but not total cholesterol (TC), [11] suggesting increased VLDL production or possibly decreased metabolism.
Sample Analyte, mg/dL size, n Mean Range Median Cholesterol 29 238 146-421 238 Triglycerides 30 156 74-340 134 HDL 28 109 61-131 113 LDL 29 92 32-249 83 VLDL 30 31 15-68 27 LDL; HDL 28 0.
Liver: The ratio of DHA to EPA in a normal VLDL appears dependent on the DHA/EPA ratio composition of liver cells at steady state.
16) Polyunsaturated FAs have been shown to reduce plasma levels of LDL and VLDL, possibly due to increased uptake into cells and increased expression of LDL receptors in the liver.
2009) reported Mean levels of TG, VLDL were higher, Mean levels of HDL, LDL were lower and Mean cholesterol level was lower in DSS than in controls.
Saglikli kontrol ve epileptik kontrol gruplari karsilastirildiginda epileptik kontrol grubunda trigliserit, VLDL degerlerinin yuksek (p<0.
Nao foram encontrados, na literatura, trabalhos que avaliaram a semente de linhaca e sua influencia sobre os niveis plasmaticos avaliados no presente trabalho, como colesterol, VLDL, LDL, HDL e triglicerides, para equinos, o que impossibilitou melhor comparacao dos resultados obtidos.
Cholesterol ester transfer protein (CETP) exchanges neutral lipids between lipoproteins, causing a net movement of cholesterol from HDL and LDL to CM and VLDL and a net movement of triglyceride in the reverse direction.
Serum was separated by centrifugation and analyzed on the same day for lipid profile (total cholesterol, triglycerides, HDL cholesterol, VLDL cholesterol, LDL cholesterol), apolipoproteins: Apo A-I ApoB 6-11).