Lipids bound

The pseudoisocyanine J-aggregate formation in the lipid bilayer was suggested to occur as follows. First the dye molecules bind to the bilayer because of electrostatic attraction and because of cation—n interaction (i.e., interaction between the dye 7i-electron cloud and the lipid head cation) then reorientation of the lipids bound to the dyes occurs so that the dye J-aggregate structures are formed. This is supposed to be due to the energy gain upon dyes stacking, while the reorientation of lipid molecules does not require energy [29],... 

The sensors discussed so far are based on ligands covalently bound to the polymer backbone. Other methods of detection - often referred to as mix and detect methods - work by simple noncovalent incorporation of the polymer with the ligand of interest. Reichert et al. generated liposomes of polydiacetylene with sialic acid for the same purpose of detection as Charych s surface-bound polymers, but realized that covalent functionalization of the polymer was not necessary [17]. Through simple mixing of the lipid-bound sialic acid with the polymer before sonication and liposome formation, they were able to form a functional colorimetric recognition system (Fig. 8). 

If a collisional quencher of the fluorophore is also incorporated into the membrane, the lifetime will be shortened. The time resolution of the fluorescence anisotropy decay is then increased,(63) providing the collisional quenching itself does not alter the anisotropy decay. If the latter condition does not hold, this will be indicated by an inability to simultaneously fit the data measured at several different quencher concentrations to a single anisotropy decay process. This method has so far been applied to the case of tryptophans in proteins(63) but could potentially be extended to lipid-bound fluorophores in membranes. If the quencher distribution in the membrane differed from that of the fluorophore, it would also be possible to extract information on selected populations of fluorophores possibly locating in different membrane environments. 

The subcellular distribution of lipid-dependent, glycosylation reactions has also been investigated in a number of plant systems. In plant cells, the situation is, however, more complicated, as their membranes often have the capability to transfer activated sugars, not only to lipid-bound saccharides201-203 and to proteins,4B-204-2,)li but also to cell-wall... 

Further studies will be needed in order to resolve the intriguing question as to how the glycosyl groups of the activated sugars that are usually found in the cytoplasm are transferred to the growing chain of the lipid-bound oligosaccharide inside the lumen of the endoplasmic reticulum. 

Both protein- and lipid-bound carbohydrates are present in milk lipid globule membrane (Table 10.2). Lipid-bound carbohydrates, present predominantly in glucosyl and lactosyl ceramides and in gangliosides,... 

Colvin155 was the first to postulate a lipid-bound D-glucose as an intermediate in the biosynthesis of bacterial cellulose. Lipid-sugar derivatives, tentatively identified as lipid-diphosphate-D-glucose, lipid-diphosphate-cellobiose, and, perhaps, higher polymers, were detected in this system.128 These lipid-sugar compounds, which were acid- and alkali-labile, seemed to be formed prior to cellulose, and their formation was inhibited by adding... 

The extraction procedure used to isolate lipids from biological tissue depends on the class of lipid desired and the nature of the biological source (animal tissue, plant leaf, plant seed, bacteria, cell membranes, etc.). Because lipids are generally less polar than other cell constituents, they may be selectively extracted with the use of organic solvents. Early studies of lipids used ether, acetone, hexane, and other organic solvents for extraction however, these solvents extract only lipids bound in a nonpolar or hydrophobic manner. In the 1950s, Folch s group reported the use of chloroform and methanol (2 1) in... 

The /3-spectrin PH domain structure was solved in a lipid-free (Zhang et al., 1995b) and lipid-bound form (Hyvonen et al., 1995). The role of the spectrin PH domain has been proposed to be part of the mechanism whereby spectrin associates directly with the membrane through binding phospholipids. The submembranous framework formed by spectrin is... 

Elemental analysis Quantitation by HPLC Analyses of the Sulfate Moiety Detection of [35s] sulfate Benzidine method Sodium rhodizinate method Estimation of lipid-bound sulfate... 

It is only comparatively recently that D-arabinose has been found to be a constituent of natural products in contrast to the frequent occurrence of its enantiomorph. Units of D-arabofuranose have been shown to form part of the molecules of the polysaccharides isolated from Mycobacterium tuberculosis (human strain),28 being identified as methyl 3,5-dimethyl-D-arabofuranoside in the products of hydrolysis, after methylation, of the somatic polysaccharide, and as the above glycoside and the methyl trimethyl-D-arabofuranoside in the lipid-bound fraction. 2-Methyl-D-arabinose has been synthesized. 

Equilibrium dialysis is used in a number of examples to analyse the ratio of lipid-bound to free analyte. Kramer et al. (1998) described the use of equilibrium dialysis by separating the liposome suspension and the water phase by a semi-permeable membrane. The analyte is dissolved in the water compartment of the system and diffuses into the liposome compartment. If equilibrium is reached, the remaining concentration of the analyte in the water compartment is determined by means of a quantification method (mainly HPLC or LCMS, fluorescence techniques) and the partition coefficient is calculated. Kramer et al. (1997) used a radio tracer substance as analyte to quantify the compound in both compartments using liquid scintillation counting. 

Membranes exhibit a common stmcture, with lipid molecules arranged in the form of one or more bilayers, or lamellae. Since lipids are generally nonfluo-rescent, lipid-bound fluorophores are an excellent tool to study this environment. These membrane probes are poorly soluble in water, and hence they partition readily into the hydrophobic regions of the membranes. The derivatives of anthroyloxy fatty acids (AF), with the fluorophore 9-anthroic acid esterfied to the 2, 6,9, 12, or 16 position along a fatty acid acyl chain (stearic acid or palmitic acid), are frequently used. The stmcture of an AF probe is shown schematically in Fig. 1... 

Extraction parameters such as solvent type, mixture ratios, metal ion concentration, pH of the aqueous phase, extraction time, and temperature influence the recovery of extracted lipids and must be validated to ensure reliable results. For example, the recovery of the acidic lipids PA and phosphatidylglycerol (PG) can be less than 30% in classic Folch and Bligh Dyer extraction, where these lipids can become bound to proteins tightly (17). Lipids bound to proteins covalently are only released under appropriate conditions, which depend on the type of lipid-protein linkage. For example, ceramides bound to protein of the comi-fled envelop in the human skin (18) can be extracted after mild alkaline hydrolysis of the ester linkage between hpid and protein. Special conditions are required for extraction of more polar lipids such as gangliosides, lysophospholipids and lysosphin-golipids, or phosphatidylinositol-phosphates. 

D.W. Borhani, D.P. Rogers, J.A. Engler, and C.G. Brouillette. 1997. Crystal structure of truncated human apolipoprotein A-I suggests a lipid-bound conformation Proc. Natl. Acad. Sci. USA. 94 12291-12296. (PubMed) (Full Text in PMC)... 

This has two consequences (1) most importantly, direct initiation of radicals in lipids bound to the heme, and (2) assurance of lipid release as LOO rather than LOOH. Chain propagation may proceed through LOO directly or through epoxyallylic peroxyl radicals from LOO cyclization. 

The crystal structure of L. migratoria apoLp-III was obtained for the protein in its lipid-free state. The lipid-bound structure of apoLp-III, however, is more interesting since it represents the active form of the protein. To date, no detailed structural reports for exchangeable apolipoproteins in complex with lipid have been reported. The crystal structure of lipid-free apoLp-III demonstrated that the five amphipathic helices orient in such a way that their hydrophobic faces are directed toward each other to form a hydrophobic core while the hydrophilic faces of the helices are exposed to solvent. It has been hypothesized that, upon binding to a... 

Haworth, Kent, and Stacey examined the structure of a lipid-bound polysaccharide of M. tvberculosis ([ajo - -25°) and found that it contains D-arabinofuraiiose, D-galactopyranose, D-mannopyranosc, and D-glucos-amine. From methylation and degradation studies, structure (21) has been proposed. 

The amphipathic helix map (Fig. 7) suggests a second and perhaps related possibility for the lipid association of the amino-terminal domain of apoE. The class A amphipathic helix located between residues 181-192 is disordered in the crystal structure (Wilson et al., 1991) but might associate with lipid when lipid is present this region has been shown to be less protease sensitive when the amino-terminal domain is lipid bound (RaW etal., 1986). 

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