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Lipoprotein, lipid component

Hurst (19) discusses the similarity in action of the pyrethrins and of DDT as indicated by a dispersant action on the lipids of insect cuticle and internal tissue. He has developed an elaborate theory of contact insecticidal action but provides no experimental data. Hurst believes that the susceptibility to insecticides depends partially on the cuticular permeability, but more fundamentally on the effects on internal tissue receptors which control oxidative metabolism or oxidative enzyme systems. The access of pyrethrins to insects, for example, is facilitated by adsorption and storage in the lipophilic layers of the epicuticle. The epicuticle is to be regarded as a lipoprotein mosaic consisting of alternating patches of lipid and protein receptors which are sites of oxidase activity. Such a condition exists in both the hydrophilic type of cuticle found in larvae of Calliphora and Phormia and in the waxy cuticle of Tenebrio larvae. Hurst explains pyrethrinization as a preliminary narcosis or knockdown phase in which oxidase action is blocked by adsorption of the insecticide on the lipoprotein tissue components, followed by death when further dispersant action of the insecticide results in an irreversible increase in the phenoloxidase activity as a result of the displacement of protective lipids. This increase in phenoloxidase activity is accompanied by the accumulation of toxic quinoid metabolites in the blood and tissues—for example, O-quinones which would block substrate access to normal enzyme systems. The varying degrees of susceptibility shown by different insect species to an insecticide may be explainable not only in terms of differences in cuticle make-up but also as internal factors associated with the stability of oxidase systems. [Pg.49]

Lipoprotein Source Diameter (nm) Density (g/mL) Composition Main Lipid Components ApolipoprotGins... [Pg.206]

Biological membranes consist of lipids, proteins and also sugars, sometimes mutually bonded in the form of lipoproteins, glycolipids and glycoproteins. They are highly hydrated—water forms up to 25 per cent of the dry weight of the membrane. The content of the various protein and lipid components varies with the type of biological membrane. Thus, in... [Pg.445]

This method is also used to measure ex vivo low-density lipoprotein (LDL) oxidation. LDL is isolated fresh from blood samples, oxidation is initiated by Cu(II) or AAPH, and peroxidation of the lipid components is followed at 234 nm for conjugated dienes (Prior and others 2005). In this specific case the procedure can be used to assess the interaction of certain antioxidant compounds, such as vitamin E, carotenoids, and retinyl stearate, exerting a protective effect on LDL (Esterbauer and others 1989). Hence, Viana and others (1996) studied the in vitro antioxidative effects of an extract rich in flavonoids. Similarly, Pearson and others (1999) assessed the ability of compounds in apple juices and extracts from fresh apple to protect LDL. Wang and Goodman (1999) examined the antioxidant properties of 26 common dietary phenolic agents in an ex vivo LDL oxidation model. Salleh and others (2002) screened 12 edible plant extracts rich in polyphenols for their potential to inhibit oxidation of LDL in vitro. Gongalves and others (2004) observed that phenolic extracts from cherry inhibited LDL oxidation in vitro in a dose-dependent manner. Yildirin and others (2007) demonstrated that grapes inhibited oxidation of human LDL at a level comparable to wine. Coinu and others (2007) studied the antioxidant properties of extracts obtained from artichoke leaves and outer bracts measured on human oxidized LDL. Milde and others (2007) showed that many phenolics, as well as carotenoids, enhance resistance to LDL oxidation. [Pg.273]

Lipoprotein class Lipid components Main apoprotein components Enzymes present Role... [Pg.163]

Very low density lipoprotein is not the only lipoprotein to be secreted by the liver. HDL is released into the blood as a nascent (immature) discoid particle. As the HDL circulates within the circulation, it matures by exchanging apoproteins and lipid components with other lipoproteins and cells. Mature spherical HDL is... [Pg.186]

Proteins may consist exclusively of a polymeric chain of amino acids these are the simple proteins. Quite often some other chemical component is covalendy bonded to the amino acid chain. Glycoproteins and lipoproteins contain sugar and lipid components, respectively. Porphyrins are frequently associated with proteins, eg, in hemoglobin. Proteins bound to other chemical components are called conjugated proteins. Most enzymes are conjugated proteins. [Pg.94]

Of the various lipid components of the lipoproteins, only the biosynthesis of cholesteryl esters has not yet been mentioned. Cholesteryl ester is the storage form of cholesterol in cells. It is synthesized from cholesterol and acyl-CoA by acyl-CoA cholesterol acyltransferase (ACAT) (fig. 20.13), which is located on the cytosolic surface of hepatic endoplasmic reticulum. Acylation of the 3 hydroxyl group of cholesterol eliminates the polarity of cholesterol and facilitates the packing of cholesterol as its ester in the core of the lipoprotein or for storage in lipid droplets within cells. [Pg.469]

The metabolism of cholesterol in mammals is extremely complex. A summary sketch (fig. 20.24) helps to draw the major metabolic interrelationships together. Cholesterol is biosynthesized from acetate largely in the liver (fig. 20.24a) or taken in through the diet (fig. 20.24b). From the intestine, dietary cholesterol is secreted into the plasma mainly as a component of chylomicrons. The triacylglycerol components of chylomicrons are quickly degraded by lipoprotein lipase, and the remnant particles are removed by the liver. Apoproteins and lipid components of the chylomicrons and remnants appear to exchange with HDL. Cholesterol made in the liver (fig. 20.24a) has several alternative fates. It can be (1) secreted into plasma as a component of VLDL,... [Pg.477]

J, 2, 4 ). The lipid component of lipoprotein was found to be made up of a diglyceride, bound by a thioether linkage to the mercapto... [Pg.195]

Pattison DI, Hawkins CL, Davies MJ (2003) Hypochlorous Acid-Mediated Oxidation of Lipid Components and Antioxidants Present in Low-Density Lipoproteins Absolute Rate Constants, Product Analysis, and Computational Modeling. Chem Res Toxicol 16 439... [Pg.491]

High-density lipoproteins (HDLs) contain a different apolipoprotein form, Apolipoprotein A. These proteins are about half lipid and half protein by weight. Phospholipids and cholesterol esters are the most important lipid components. HDL is sometimes referred to as good cholesterol because a higher ratio of HDL to LDL corresponds to a lower rate of coronary artery disease. [Pg.8]

A variety of studies have suggested that in the presence of lipid, the apoprotein components of lipoproteins assume regions of high helical content which exhibit two faces of opposite polarity. When these proteins are on the surface of a lipoprotein particle, the nonpolar face can interact with the nonpolar lipid components of the particle, whereas the polar face interacts with the polar head groups of cholesterol and phospholipid, and the aqueous environment of the bloodstream (Fig. 2). [Pg.52]

Vitamin E is the major hydrophobic chain-breaking antioxidant that prevents the propagation of free radical reactions in the lipid components of membranes, vacuoles and plasma lipoproteins. [Pg.113]

The major lipid components of chylomicrons and VLDL are triacylglycerol, whereas the predominant lipids in LDL and HDL are cholesterol and phospholipids respectively. The protein part of lipoprotein is known as apoprotein. Lipoproteins occur in milk, egg-yolk and also as components of cell membranes. [Pg.86]

The only common major lipid component of vertebrate and insect lipoproteins is phospholipid (PL). Lipophorin PLs have been characterized in only a few insect species (Table II). The major PLs are phosphati-... [Pg.373]

The elucidation of the structure of any lipoprotein, i.e., the organization of the protein and lipid components, is a challenging problem, because it relies on several techniques that give only partial and approximate information. Structural models should be consistent with experimental data that characterize the physiological role and the physicochemical properties of the lipoprotein and its components. Considerable effort has been expended to fit experimental data to structural models of mammalian lipoproteins (Zilversmit, 1965 Sata et al., 1972 Schneider et al., 1973 Havel, 1975 Verdery and Nichols, 1975 Shen et al., 1977 ... [Pg.388]

A totally different rationale has to be applied to the transport of hydrocarbons. These extremely hydrophobic compounds seem to reside in the interior of the lipophorin particles. A mechanism involving uptake and degradation of the lipoprotein might be possible for the transport of hydrocarbons to the epidermal cells. This type of mechanism might be important in certain stages of insect development, when the lipoprotein could deliver amino acids and other lipid components necessary for the construction of the cuticle. A similar process may also exist for the delivery of carotenoids and sterols. [Pg.408]

Separate lipid components such as chylomicrons from other components of plasma or serum, and lipoproteins from one another (see Chapter 26). [Pg.19]

Neurons rely upon a ready supply of cholesterol for maintaining a broad array of physiological functions such as membrane synthesis, myeUn maintenance, electrical signal transduction, synaptic transmission, and plasticity. Cholesterol metabolism in the CNS is unique compared with the rest of the body. Because of the existence of the blood-brain barrier (BBB), almost all the sterol required for new membranes comes from de novo synthesis within the CNS [33]. In addition, the brain has evolved highly efficient mechanisms to maximize the utihzation of cholesterol. UnUke other membrane lipid components, cholesterol cannot be synthesized at neuronal terminals. Therefore, synaptic function depends largely on cholesterol supplied from either axonal transport from the cell body and or uptake of Upidated ApoE produced by astroglia via neuronal lipoprotein receptors. [Pg.90]


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See also in sourсe #XX -- [ Pg.861 ]

See also in sourсe #XX -- [ Pg.488 , Pg.489 , Pg.556 ]




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Lipoproteins components

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