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 ?
Caixas et al., "Effect of glycemic optimization on electronegative low-density lipoprotein in diabetes: relation to nonenzymatic glycosylation and oxidative modification," The Journal of Clinical Endocrinology and Metabolism, vol.
Association between polymorphisms of lipoprotein lipase gene and chicken fat deposition.
RESULTS: Statistical analysis showed that the levels of total cholesterol (Table 1, Chart 1), triglycerides (Table 2, Chart 2) very low density lipoproteins(Table 3, Chart 3), and low density lipoproteins (Table 4, Chart 4) were significantly raised in Type 2 Diabetic patients while levels of high density lipoproteins were lowered.(Table 5, Chart 5).
Despite the significance difference which has been seen among pre-test and post-test, due to the lack of significant difference between empirical and control groups in this variable after the empirical group did the exercises, it was concluded that aerobic exercises hasn't had a significant impact on the rate of the very low density lipoprotein of the working women.
Detailed clinical assessments of a personal and family history of premature cardiovascular disease, physical signs and lipoprotein profiles will assist in the diagnoses listed in Table 2.
Various drugs target different lipids; therefore, lipoprotein analysis is essential before starting lipid-altering medications.
Analytical methods that are able to test various lipoprotein fractions and subfractions are essential for the detection of various lipid disorders.
Keywords: Tissue factor, Oxidised low density lipoprotein, Lectin-like oxidised LDL receptor, Beta (2)-Glycoprotein I.
Base change was found to be the possible cause of gain in function of LPL mRNA and resulted in lower susceptibility to inhibitrion for translation.5 The aim of this study was to investigate the relationship of lipoprotein lipase (LPL) gene polymorphism with serum contents of triglycerides and high-density lipoprotein (HDL) cholesterol among hyperlipidemia families.
However the result of the present study indicate that higher levels of non-fasting triglycerides and Apo-B were observed in all subject regardless myocardial infarction, The marked increase of non-fasting triglycerides with associated Apo lipoprotein B indicate that these elevated non-fasting triglyceride levels were associated with increased risk of MI, IHD in men and women.
The IDL lipoprotein is the precursor of (low-density lipoprotein) LDL, which is also known as the bad cholesterol.

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