Lipid-protein isolates

The actions of proteins isolated from sea anemones, or other coelenterates, involve mechanisms different from those described for saponins. Thus, hemolysins from sea anemone R macrodactylus are capable of forming ion channels directly in membranes (98). The basic protein from S. helianthus also forms channels in black-lipid membranes. These channels are permeable to cations and show rectification (99). This ability of S. helianthus toxin III to form channels depends upon the nature of the host lipid membrane (100). Cytolysin S. helianthus binds to sphingomyelin and this substance may well serve as the binding site in cell membranes (101-106). 

Because of their very complex chemical structures and heterogeneity, melanins are difficult to extract, separate, and characterize from tissues. Eumelanins are insoluble in water and organic solvents. They can be extracted from tissues with strong chemicals that are capable of removing lipids, proteins, and other tissue components but also lead to the formation of degradation products. Enzymatic procedures were developed for the isolation of eumelanins from mammalian hair and irises. The first step is sequential digestion with protease, proteinase K, and papaine in the presence... 

Sample preparation used to extract proteins from cells prior to analysis is an important step that can have an effect on the accuracy and reproducibility of the results. Proteins isolated from bacterial cells will have co-extracted contaminants such as lipids, polysaccharides, and nucleic acids. In addition various organic salts, buffers, detergents, surfactants, and preservatives may have been added to aid in protein extraction or to retain enzymatic or biological activity of the proteins. The presence of these extraneous materials can significantly impede or affect the reproducibility of analysis if they are not removed prior to analysis. 

Droplets of different density and lipid protein ratios ranging from about 1.5 1 to 40 1 have been isolated from bovine mammary gland. Triglycerides are the major lipid class in droplets of all sizes and represent increasingly greater proportions of total droplet mass in increasingly less dense droplet preparations. Surface coat material of droplets contains cholesterol and the major phospholipid classes found in milk, i.e. sphingomyelin, phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol and phosphatidyl-serine. 

Nguyen, T.T. 1999. The cholesterol-lowering action of plant stanol esters. J. Nutr. 129, 2109-2112. Ni, W., Yoshida, S., Tsuda, Y., Nagao, K., Sato, M., and Imaizumi, K. 1999. Ethanol-extracted soy protein isolate results in elevation of serum cholesterol in exogenously hypercholesterolemic rats. Lipids 34, 713-716. 

Many pyrazines were isolated and identified in cooked foods, especially in cooked meats (27). Pyrazines comprised over 40% of the volatile compounds found in cooked pork liver (28). Two pyrazines, 2-methyl-3(or 6)-pentylpyrazine and 2,5-dimethyl-3-pentylpyrazine were among 52 volatiles identified as lipid-protein-carbohydrate interaction products in a zein regular or waxy corn starch-corn oil model system (7). 

M44. Morton, R. E., and Zilversmit, D. B., Inter-relationship of lipids transferred by the lipid transfer protein isolated from human lipoprotein-deficient plasma. /. Biol. Chem. 258, 11751-11757 (1983). 

These studies demonstrate that treatments that have been reported to modify the heat stability of milk also may change the distribution of tracer milk proteins between the physical phases of milk. Analysis of these interactions may provide useful information about the mechanisms of these effects. In unpublished experiments, we have extended this approach for studying homogenized milk-based systems, also containing a lipid phase, to investigate lipid-protein interactions. Dual-label experiments, for example in milk containing M-/3-L and 3H-methyl-/c-casein, could be applied to the isolation and characterization of protein complexes in milk. Labeled caseins could prove valuable as probes for elucidating micelle structure. 

Even though our understanding of the possible types of lipid-protein interactions in membranes has developed only recently, it was evident to early investigators that neutral solvents per se were the most effective for isolation purposes. Perhaps the most widely used solvent extraction procedure for many years was that employing a mixture of ethanol-diethyl ether (usually 1 3, v/v). This technique involved extraction of a tissue with this solvent combination for several hours at 55-60°C (Bloor, 1928). However, as more refined techniques were developed for the detection and assay of lipids, it became evident that this solvent (and condition) could have a deleterious... 

Blood plasma contains a number of soluble lipoproteins, which are classified, according to their densities, into four major types. These lipid-protein complexes function as a lipid transport system. Isolated lipids are insoluble in blood, but they are rendered soluble, and therefore transportable, by combination with specific proteins, the so-called lipoproteins. There are four basic types in human blood (1) chylomicrons, (2) very low density lipoproteins (VLDL), (3) low-density lipoproteins (LDL). and (4) high-density lipoproteins (HDL). Their properties are summarized in Table 6.2. 

Question Some of the integral proteins isolated from membranes have high molecular weights. How might these fit into the lipid bilayer ... 

Starch in plants is accompanied by water, metal ions, lipids, proteins, sterols (such as saponins), and alkaloids (as in such exotic plants as Diascoracea).649 Several of these components can be washed out by the isolation of starch, some of them are extractable with organic solvents, and some are volatized by steam treatment. With the exception of metal ions (preceding article, p. 263), the foregoing components form physical mixtures with starch and do not chemically bond with either amylose or amylopectin. Therefore, one may assume that amylose and amylopectin form inclusion complexes with organic components that are similar to those mentioned in the preceding article. 

Stuchell, Y.M., and Krochta, J.M. (1995). Edible coating on frozen king salmon effect of whey protein isolate and acetylated monoglycerides on moisture loss and lipid oxidation. J. FoodSci. 60, 28-31. 

Hu, M., McClements, D.J., and Decker, E.A. (2003). Lipid oxidation in com oil-in-water emulsions stabilized by casein, whey protein isolate, and soy protein isolate. J. Agric. Food Chem. 51, 1696-1700. 

The importance of zinc to growth and development in all forms of life was first established through zinc deficiency studies of microorganisms followed by those in plants and animals see Nutritional Aspects of Metals Trace Elements) The involvement of zinc in a wide variety of metabolic processes including carbohydrate, lipid, protein, and nucleic acid synthesis and degradation paralleled the technical advances in analytical methods that could detect the presence of zinc in minute amounts coupled with advances in the methodology for protein isolation and purification. 

This highly selective separation procedure is used mainly for isolation and analysis of bioactive components (e.g. lipids, proteins). 

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