Lipid distribution

Proteins that can flip phospholipids from one side of a bilayer to the other have also been identified in several tissues (Figure 9.11). Called flippases, these proteins reduce the half-time for phospholipid movement across a membrane from 10 days or more to a few minutes or less. Some of these systems may operate passively, with no required input of energy, but passive transport alone cannot establish or maintain asymmetric transverse lipid distributions. However, rapid phospholipid movement from one monolayer to the other occurs in an ATP-dependent manner in erythrocytes. Energy-dependent lipid flippase activity may be responsible for the creation and maintenance of transverse lipid asymmetries. 

Allan, D., Mapping the lipid distribution in the membranes of BHK cells, Molec. Membr. Biol. 13, 81-84 (1996). 

Proulx [30] summarized the published lipid compositions of BBM isolated from epithelial cells from pig, rabbit, mouse and rat small intestines. Table 3.1 shows the lipid make-up for the rat, averaged from five reported studies [30], On a molar basis, cholesterol accounts for about 50% of the total lipid content (37% on a weight basis). Thus, the cholesterol content in BBM is higher than that found in kidney epithelial (MDCK) and brain endothelial cells (Table 3.1). Slightly different BBM lipid distribution was reported by Alcorn et al. [31] here, the outer (luminal) leaflet of the BBM was seen to be rich in sphingomyelin content, while the inner leaflet (cytosol) was rich in PE and PC. Apical (brush border) and basolateral lipids are different in epithelia. The basolateral membrane content (not reported by... 

Figure 21.11 Characteristic lipid distribution in a rodent brain. Reprinted with permission from Shimma et al.13...

Regarding the interference of lipids and fatty acids in preparation of LPC, Nagy et al. (15) made an extensive study of this problem and determined, as indicated in Table VII, that the lipid content and total lipid distribution in some green protein fractions is indeed significant and can present a problem with protein extractability and purification. They indicated however, most of the lipid appeared to come from extraction of cell walls and ruptured cellular contents during the maceration process. 

Table VII. Lipid Distributions of Green Protein Fractions3 ...

Tropical Leaves Total Extracted Lipids 8 Lipid/ Crude Protein Total Lipid Distribution, % Nonsapon- Fatty ifiables Acids Residue ... 

Membranes and models membrane organization (e.g. membrane domains, lipid distribution, peptide association, lipid order in vesicles, membrane fusion assays, etc.)... 

K. Gaus, M. Rodriguez, K. R. Ruberu, I. Gelissen, T. M. Sloane, L. Kritharides, and W. Jessup. Domain-specific lipid distribution in macrophage plasma membranes../. Lipid Res. 46 1526-1538 (2005). 

Lockheart MJ, van Bergen PF, Evershed RP, Chemotaxonomic classification of fossil leaves from the Miocene Clarkia lake deposit, Idaho, USA based on n-alkyl lipid distributions and principal component analyses, Org Geochem 31 1223— 1246, 2000. 

Human Serum Lipoproteins Percentage Protein Lipid Distribution"... 

Ultrastructural changes on chloroplasts of mesophyll cells no effect on chlorophyll and lipid distribution (Beaumont et al. 1980 Grenier etal. 1987)... 

Thus far, it could be shown that stable liposomes can be prepared by polymerization of lipids. These vesicle systems, however, are still far away from being a real biomembrane model. As of now, they do not show any typical biological behavior such as surface recognition, enzymatic activities, variable lipid distribution, and the ability to undergo fusion. 

An infrared image study of corn and oat-flour-based extrudates was reported by Cremer and Kaletunc.71 Spatial distributions of starch, protein and lipid were determined. Starch was ubiquitous over the entire cross-section. The protein distribution possessed the smallest degree of uniformity and was inversely correlated with the starch distribution. The lipid distribution was correlated with neither the starch nor the protein distribution. 

Krasnoshchekov, G. P., Kashin, V. A. Kontrimavichus, V. L. (1978). [Dynamics of lipid distribution in the developing larvae of Aploparaxis polystictae (Cestoda Hymenolepididae).] In Russian. Doklady Akademii Nauk SSSR, 241 1481 1. [HA/51/1371]... 

Lipids in foods vary from traces as in cereals to 30-50% as in nuts. The physical state and distribution of lipids vary considerably among food items. In each item lipid distributions affect its flavor as it undergoes chemical reactions and act as a flavor components vehicle or partitioning medium. Furthermore, lipids have a pronounced effect upon the structure of food items. Fatty acids of neutral (triglycerides) and polar lipids of beef and pork are tabulated in Table III. 

Nonuniform lipid distribution in membranes lipid rafts... 

Asymmetry in the lipid distribution over the bilayer could also be controlled in a similar way by the lateral packing pressure, which is likely to differ between constituent monolayers, due to the distinct chemical environments inside and outside the membrane. The enzymes involved may also be distributed asymmetrically. A configuration with constant, but nonzero, mean curvature, shown in Fig. 5.7, reflects such a situation. A membrane-spatming protein can then be viewed as a sensor of the lateral packing pressure in both monolayers. This speculation has some experimental justification. In a recent study of chromaffin granules, trans-membrane lipid asymmetry was shown to be induced by an ATP-dependent "flippase" [35]. 

Xie, S., Yi, Y., Huang, J., Hu, C., Cai, Y., Collins, M. Baker, A. (2003) Lipid distribution in a subtropical southern China stalagmite as a record of soil ecosystem response to paleoclimate change. Quaternary Research 60, 340-347. 

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