Lipoproteins components

FIGURE 25.38 Lipoprotein components are synthesized predominantly in the ER of liver cells. Following assembly of lipoprotein particles red dots) in the ER and processing in the Golgi, lipoproteins are packaged in secretory vesicles for export from the cell (via exocy-tosis) and released into the circulatory system. 

The pathogenic mechanisms responsible for the association of musculoskeletal abnormalities with hypercholesterolaemia remain obscure. However, it has been hypothesized that the deposition and modification of lipoprotein components within and around the joint of patients with hyperlipidaemia-associated arthropathy results in a pro-inflammatory response, giving rise to articular disorders (Prete et al., 1993). 

ApoA-1 is the major structural lipoprotein component of HDL particles. Transgenic over-expression of apoA-1 has been well documented to correlate very strongly with antiatherogenic effects seen in a number of animal models [89-91]. The genetic deficiency of apoA-1 in humans has also been linked to low levels of HDL and premature atherosclerosis [90-92]. It is believed that infusion of apoA-1 enhances the ABCAl-mediated cholesterol efflux from macrophages [93]. During the last decade, significant efforts have been spent to find small... 

Sundheim, G., Zimmer, T.-L., Astrup, H.N. 1983. Induction of milk lipolysis by lipoprotein components of bovine blood serum. J. Dairy Sci. 66, 400-406. 

Cohn EJ, Strong LE, Hughes WI, et al. Preparation and properties of serum and plasma proteins. IV. A system for the separation into fractions of the protein and lipoprotein components of biological tissue and fluids. J Am Chem Soc 1946 68 459-75. 

For molecular modeling of the lipoproteins, values for the partial specific volumes of the lipoprotein components are required. The partial specific volume of an aqueous egg yolk lecithin suspension is 0.984 ml/g (Hauser and Irons, 1972), and this provides a reasonable approximation for the partial specific volume of the phospholipid occupying the surface monolayer of a lipoprotein. The reciprocal of the density of liquid triolein (Small, 1986) yields its partial specific volume, 1.102 ml/g, and provides a reasonable approximation for triglyceride dissolved in the cholesteryl ester-filled core of the LDL. For cholesterol, the partial specific volume of 1.021 ml/g measured in benzene (Haberland and Reynolds, 1973) has been employed. The value of 0.740 ml/g employed for the partial specific volume of apoBlOO was determined from its amino acid composition (Lee et al., 1987). A value of 0.60 ml/g was used for the partial specific volume of the carbohydrate moiety. One important parameter, the partial specific volume of cholesteryl ester, remains to be determined. As will be shown below, its value is estimated to be 1.058 ml/g. 

When methylene chloride is absorbed through the lungs, it is thought that it will dissolve in the lipoprotein components of the blood and be distributed from the systemic circulation to the body organs. 

The theory that volatile anesthetics may act by specific binding to lipoprotein components of nerve tissue membranes or of the membrane itself has some experimental evidence. The use of 19F nuclear magnetic resonance spectroscopy with halothane indicated that saturable anesthetic sites for halothane exist in living rats at 2.5% inspired gas. The authors consider this to support the idea that volatile anesthetics do act specifically even stereospecifically (Moody etal., 1994). 

The lipoprotein components of blood plasma play indispensable roles in transporting lipids. 

For separation and quantitation of human serum lipoproteins, several technics are currently used. These technics include preparative ultracentrifugation (1-3), gel filtration (1,4), selective precipitation with polyanion/divalent cation reagents (1,5), electrophoresis (1,6), affinity choromatography (7), and ultrafiltration (8). For effective separation of all major lipoprotein classes, a combination procedure consisting of several technics above mentioned is frequently used. Therefore, this leads to difficulties, that is, the loss and alteration or decomposition of lipoprotein components due to time consuming experimental procedures. ... 

Cooper [5] reviewed early work on the binding of penicillin to a lipoprotein component in the membrane of S. aureus, and further work [Rogers, 3,62] confirms the link between penicillin binding, inhibition of mucopeptide synthesis, and the antibiotic action of penicillin. The relation of penicillin binding to penicillinase induction is less clear. 

It can be expected that all plasma lipoprotein classes, defined in one way or another, consist of a variety of subfractions, simply because plasma lipoproteins form a dynamic system. Plasma lipoprotein metabolism starts as soon as the nascent particles are secreted. Subsequent intravascular metabolism includes the actions of lipoprotein lipase, hepatic lipase, lecithin cholesterol acyltransferase (LCAT), and lipid transfer proteins (LTP). In addition, most lipoproteins can bind to lipoprotein receptors. This can be foUowed by uptake and irreversible intracellular degradation of the holo-particle, or by reappearance in plasma of a modified form of the lipoprotein. The modifications may be due to the transfer of cellular lipids to plasma lipoproteins or to the specific transfer of lipoprotein components to the cells. Both mechanisms may include retroendocytosis. 

Stender S, Zilversmit DB (1981) Transfer of plasma lipoprotein components and of plasma proteins into aortas of cholesterol-fed rabbits. Molecular size as a determinant of plasma lipoprotein influx. Arteriosclerosis 1 38-49... 

Fig. 1. Lipoprotein metabolism. The flow of the fatty acyl moieties of the triglyceride-rich lipoproteins originates in the intestine and in the liver with the synthesis of carrier components and the assembly of these components into lipoproteins. After secretion, exchange of lipoprotein components produce mature lipoproteins which are then metabolized by lipoprotein lipase at the capillary endothelium. Lipoprotein turnover eventually produces smaller remnant lipoproteins that are removed from the circulation for intracellular processing of the molecular components.

Dynamics of lipoprotein structure. The individual rate constants for absorption and desorption of the lipoprotein components from the lipoprotein surface are designated d, ... 

Troup, J. M. Method for analyzing blood for lipoprotein components. U.S. Pat. Appl. Publ. US... 

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