lipoprotein

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lipoprotein

(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.

Lipoprotein

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

lipoprotein

[‚lip·ə′prō‚tēn]
(biochemistry)
Any of a class of conjugated proteins consisting of a protein combined with a lipid.
References in periodicals archive ?
Se encontraron diferencias estadisticamente significativas en las concentraciones de trigliceridos (300,06 +/- 165,59 en el grupo A mg/dl comparado con 195,69 +/- 52,39 mg/dl en el grupo B; p > 0,05, figura 1), HDL-C (51,09 +/- 16,13 mg/dl para el grupo A comparado con 67,29 +/- 14,26 mg/dl para el grupo B; p < 0,05, figura 2), VLDL (grupo A 79,03 +/- 38,08 mg/dl comparado con el grupo B 44,54 +/9,12 mg/dl; p < 0,05, figura 3) y Lp(a) (28,62 +/- 5,24 mg/dl para el grupo A comparado con 18,60 +/- 3,44 mg/dl para el grupo B; p < 0,05, figura 4).
Hypertriglyceridaemia results from decreased removal of the CM and/or VLDL, but overproduction of VLDL may occur in certain cases such as patients with diabetes mellitus.
These positive research findings support the beneficial effects of two types of ghee outlined in the ancient Ayurveda system and the texts; 5% curd ghee was found to be better than the 5% milk cream ghee; 5% Curd Ghee has shown to lower total cholesterol, LDL, VLDL, triglycerides levels and cholesterol ratio in our experimental model.
It is observed that on the 2nd day mean serum HDL level decreased whereas the mean serum VLDL level increased significantly.
001) reduction in serum triglycerides, cholesterol, LDL and VLDL levels with concomitant significant (p Less than 0.
Asi mismo, en condiciones normales se da un proceso de reesterificacion de trigliceridos (TG) en el hepatocito, que luego salen para ser utilizados como fuente de energia en otros tejidos y para la sintesis de leche; para que esto ocurra el higado debe ser capaz de sintetizar la apo B derivada de las VLDL; pero si la cantidad de TG reesterificado en el higado excede la capacidad de este para sintetizar las VLDL, los TG son depositados en el adipocito en forma de gotas grasa o como infiltrados de grasa en el higado, musculos estriados, musculo cardiaco, adrenales y rinones (12).
Several factors such as an increased de novo lipogenesis and an impaired secretion of VLDL in the liver are responsible for the development of non-alcoholic fatty liver disease (Postic and Girard, 2008).
O metodo para determinacao do colesterol total (CT), triglicerides (TG), VLDL e HDL foi automacao enzimatica, e para estabelecer o valor do LDL o laboratorio utilizou a equacao de Friedewald (LDL = CT - [HDL + TG/5]).
Este colesterol puede ser almacenado, eliminado como acido biliar o enviado a la circulacion para formar parte de las VLDL (Montgomery, 1998; Breininger & Pintos, 2007; King, 2011b).
The frequencies of classical CAD risk factors such as obesity, hypertension, smoking, family history of CAD, lipid levels like total cholesterol, triglycerides, LDL, VLDL were higher in patients than in controls (Table I) but these were not statistically different between SS and SR genotypes (Table II).
The first reagent contains a-cyclodextrin and dextran sulfate to stabilize LDL-C, VLDL, and chylomicrons.