Lipoproteins groups

Apoliprotein. Any of the protein constituents of lipoproteins, grouped by function in four classes A, B, C, and E (the former apolipoprotein [apo] D is now apo A-111). Apoptosis. Fragmentation of a cell into membrane-bound particles that are eliminated by phagocytosis. Programmed cell death. 

P. L. Workman, and J. Hirschfeld Gamma-globulin, group specific, and lipoprotein groups in a U.S. white and negro population. Nature (Lond.) 202, 561—663 (1964). 

Cholesterol is a principal component of animal cell plasma membranes, and much smaller amounts of cholesterol are found in the membranes of intracellular organelles. The relatively rigid fused ring system of cholesterol and the weakly polar alcohol group at the C-3 position have important consequences for the properties of plasma membranes. Cholesterol is also a component of lipoprotein complexes in the blood, and it is one of the constituents oiplaques that form on arterial walls in atherosclerosis. 

Fibric acid derivatives, the third group of antihyperlipi-demic drugs, work in a variety of ways. Clofibrate (Atromid-S), acts to stimulate the liver to increase breakdown of very-low-density lipoproteins (VLDL) to low-density lipoproteins (LDL), decreasing liver synthesis of... 

Cholesterol (Figure 14-17) is widely distributed in all cells of the body but particularly in nervous tissue. It is a major constituent of the plasma membrane and of plasma lipoproteins. It is often found as cholesteryl ester, where the hydroxyl group on position 3 is esteri-fied with a long-chain fatty acid. It occurs in animals but not in plants. 

Four Major Groups of Plasma Lipoproteins Have Been Identified... 

The nonpolar lipid core consists of mainly triacylglycerol and cholesteryl ester and is surrounded by a single surface layer of amphipathic phospholipid and cholesterol molecules (Figure 25-1). These are oriented so that their polar groups face outward to the aqueous medium, as in the cell membrane (Chapter 14). The protein moiety of a lipoprotein is known as an apo-lipoprotein or apoprotein, constituting nearly 70% of some HDL and as litde as 1% of chylomicrons. Some apolipoproteins are integral and cannot be removed, whereas others are free to transfer to other hpoproteins. 

Four major groups of lipoproteins are recognized Chylomicrons transport lipids resulting from digestion and absorption. Very low density lipoproteins (VLDL) transport triacylglycerol from the liver. Low-density lipoproteins (LDL) deliver cholesterol to the tissues, and high-density lipoproteins (HDL) remove cholesterol from the tissues in the process known as reverse cholesterol transport. 

TAG-CH3 and TAG-CH2-, acyl chain terminal-CH3 and bulk (-CH2-)n groups, respectively, of fatty acids (predominantly triacylglycerols) associated with chylomicron- and very low-density lipoprotein (VLDL) Thr, threonine-CHs Val, valine-CHs. The asterisk In spectrum (b) denotes a radiolytically-generated 2.74 p.p.m. 

Antibodies to very low density lipoprotein (VLDL) and LDL have been detected in the serum of patients with RA, but not control groups (Lazarevic et al., 1993). In these studies, 38% of patients with active RA tested positive for anti-VLDL/LDL antibodies whilst these autoantibodies were not detected in patients with psoriatic arthritis, osteoarthritis or healthy subjects. Lipoproteins were found in the dissociated components of circulating immune complexes in the serum of 30% of the RA patients. It was concluded that dyslipoproteinaemia in some RA patients may be due to an autoimmune component of the disease. 

FIGURE 9-1. Lipoprotein structure. Lipoproteins are a diverse group of particles with varying size and density. They contain variable amounts of core cholesterol esters and triglycerides, and have varying numbers and types of surface apolipoproteins. The apolipoproteins function to direct the processing and removal of individual lipoprotein particles. (Reprinted from LipoScience, Inc. with permission.)... 

Hofer F. Members of the low density lipoprotein receptor family mediate cell entry of a minor group common cold virus. Proc Natl Acad Sci USA 1994 91 1839-1842. 

Hyperlipemia may manifest itself by an increased concentration of lipids, or certain groups thereof. For example, hypercholesterolemia and hypertriglyceri-demia may be mentioned in this connection. Since practically all the blood plasma lipids make part of lipoproteins, hyperlipemias may be reduced to one of the hyper-lipoproteinemia forms which differ in the varied ratios of plasma lipoproteins of different groups. 

Biotin-hydrazide has been used to biotinylate antibodies at their oxidized carbohydrate residues (O Shanessy et al., 1984, 1987 O Shanessy and Quarles, 1985 Hoffman and O Shannessy, 1988), to modify the low-density lipoprotein (LDL) receptor (Wade et al., 1985), to biotinylate nerve growth factor (NGF) (Rosenberg et al., 1986), and to modify cytosine groups in oligonucleotides to produce probes suitable for hybridization assays (Reisfeld et al., 1987) (Chapter 27, Section 2.3). 

A protective lipid profile, with reduction of total cholesterol and LDL and a modest increase in high-density lipoprotein (HDL), has been associated with oral estrogen therapy (Writing Group for the PEPI Trial 1995). This effect, however, has been considered negligible when compared with the benefits traditionally ascribed to estrogens (Marsh et al. 1999). 

Lipidated peptides embodying the characteristic linkage region found in the parent lipoproteins and bearing additional functional groups, which could be traced in biological systems or which allowed for their use in biophysical experiments, were used successfully in model studies. However, such model studies only provide a limited amount of information. In order to approximate the situation in a biological system more precisely, experiments with differently lipidated proteins are required. 

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