Lipid acyl chains

Samuni AM, Barenholz Y. Stable nitroxide radicals protect lipid acyl chains from radiation damage. Free Radicals Biol Med 1997 22 1165-1174. 

Natural biological membranes consist of lipid bilayers, which typically comprise a complex mixture of phospholipids and sterol, along with embedded or surface associated proteins. The sterol cholesterol is an important component of animal cell membranes, which may consist of up to 50 mol% cholesterol. As cholesterol can significantly modify the bilayer physical properties, such as acyl-chain orientational order, model membranes containing cholesterol have been studied extensively. Spectroscopic and diffraction experiments reveal that cholesterol in a lipid-crystalline bilayer increases the orientational order of the lipid acyl-chains without substantially restricting the mobility of the lipid molecules. Cholesterol thickens a liquid-crystalline bilayer and increases the packing density of lipid acyl-chains in the plane of the bilayer in a way that has been referred to as a condensing effect. 

There is an abrupt decrease in the lateral diffusion coefficient of DPPC upon the phase transition from the GI phase to the Gi phase. This is because the acyl-chain region is being packed even more efficiently in the Gi phase than in the GI phase, and the hydrocarbon volume in the Gi phase is smaller than in the GI phase. Also, in the Gi phase, the lipid acyl-chains from the opposing bilayer leaflets interdigitate. In order for a phospholipid molecule to diffuse it has to circumvent the nearby interdigitated molecules which hinder diffusion. 

Several studies have dealt with the influence of lipids on conformational equilibria in cytochrome c via hydrophobic and electrostatic interactions. The binding of sodium dodecyl sulfate monomers and micelles was reported to cause a transition of cytochrome c to a state B2 which is of potential physiological relevance. The interplay between heme only state changes and secondary structure changes was analyzed by freeze-quench and stopped-flow experiments.276 The response of the heme spin state to lipid acyl chains in cytochrome c was... 

Along a more biological approach, D. Chapman 116) has described the biosynthetic incorporation of diacetylene acids into the biomembranes of Acholeplasma laidlawii A, an unsaturated fatty acid auxotroph bacterium. As much as 90% of the membrane lipid acyl chains were found to consist of C20-diynoic acid. Upon irradiation with UV-light, the cells and isolated membranes become coloured, due to the crosslinking of lipids by photopolymerization. 

Thickness Hydrocarbon solvent and lipid acyl chain length, reflects extent of low dielectric zone Chemical/Steric... 

Modern methods of vibrational analysis have shown themselves to be unexpectedly powerful tools to study two-dimensional monomolecular films at gas/liquid interfaces. In particular, current work with external reflection-absorbance infrared spectroscopy has been able to derive detailed conformational and orientational information concerning the nature of the monolayer film. The LE-LC first order phase transition as seen by IR involves a conformational gauche-trans isomerization of the hydrocarbon chains a second transition in the acyl chains is seen at low molecular areas that may be related to a solid-solid type hydrocarbon phase change. Orientations and tilt angles of the hydrocarbon chains are able to be calculated from the polarized external reflectance spectra. These calculations find that the lipid acyl chains are relatively unoriented (or possibly randomly oriented) at low-to-intermediate surface pressures, while the orientation at high surface pressures is similar to that of the solid (gel phase) bulk lipid. 

Figure 3.32 shows the 1H-NMR spectrum of DPPC vesicles in the presence of 5 mM Pr. It shows the separation of resonance signals of the inner (1) and outer (O) choline head groups and the proton resonance of the lipid acyl chains (H) and of the terminal methyl group (M) [121]. Lysed vesicles were obtained by cycling the DPPC... 

Small-angle X-ray diffraction was used to identify the time-averaged location of amiodarone in a synthetic lipid bilayer. The drug was located about 6 A from the center of the lipid bilayer (Figure 4.13) [125, 126]. A dielectric constant of k = 2, which is similar to that of the bilayer hydrocarbon region, was used to calculate the minimum energy conformation of amiodarone bound to the membrane. The studies were performed below the thermal phase transition and at relatively low hydration of lipid. The calculated conformation differed from that of the crystal structure of amiodarone. Even though the specific steric effects of the lipid acyl chains on the confor-... 

Several studies have been performed to analyze the effect of membrane composition on accumulation and transport of antineoplastic drugs. In particular, the role of anionic lipids in transport and passive diffusion, as well as on the binding of doxorubicin and its effect on the degree of order of lipid acyl chains was investigated. Using 2H-NMR spectroscopy the effect of doxorubicin on mixed bilayers of DOPS, DOPA, dioleoylphosphatidylcholine (DOPC), and DOPE was studied. It was found that doxorubicin does not affect acyl chain order of pure zwitterionic phospholipids but dramatically influences that of anionic lipids [112]. At 25 °C, in bilayers consisting of 67... 

Zucchi MR, Nascimento OR, Faljoni-Alario A et al (2003) Modulation of cytochrome c spin states by lipid acyl chains a continuous-wave electron paramagnetic resonance (CW-EPR) study of haem iron. Biochem J 370 671-678... 

Tiburu et al." investigated the influence of hCBi and hCB2/ G-protein-coupled receptors, on the dynamics of lipid headgroups and lipid acyl chains of the POPC bilayer. The authors described the reduction of the CSA width of 31P spectra in the lipid headgroups, which shows the local motions of this part. These disruptions result from the impact of hCBi and hCB2 peptides which can be either localised on the membrane surface or incorporated in hydrophobic core and leaves this lipid bilayer. 

The last group of amphiphiles contains sterols that are present in the membranes of cells. The most popular among them is cholesterol (Choi), which can be easily incorporated in lipid bilayers, increasing their rigidity and making them less permeable, due to the interactions taking place with phospholipids in lipid membranes which result in modification of the lipid acyl-chain conformation. 

If there is some molecular motion with characteristic times on the order of ICT sec, the NMR spectrum will no longer have the Pake doublet lineshape discussed earlier. For example, in gel-phase bilayers a perdeuterated lipid acyl chain will have a broad, relatively featureless spectmm, as shown in Fig. 3. These spectra do not lend themselves to easy analysis The molecular motion in the membrane is not rapid enough to be axially symmetric (see the description of the fluid bilayer below) on the NMR time scale but is fast enough to influence the average value of the quadrupolar interaction and thus the splittings of the individual labels. 

Protein-lipid interactions and particularly peptide-lipid interactions have been studied in supported bilayers by attenuated total reflection (ATR) FTIR spectroscopy. A slightly dated, but still valid comprehensive review on this method applied to supported bilayers has been published (20). Because IR light probes the vibrational properties of different classes of covalent bonds, this method is useful to examine lipids, peptides, and interactions between the two in the same sample. The most common parameter for assessing lipid structure and order is to study the stretching vibrations of the lipid acyl chains, for example as a function of peptide concentration or temperature. Such studies have lead to the conclusion that fusion peptides from viruses increase the lipid chain order of fluid phase bilayers and that... 

Peroxyl Radicals Secondary peroxyl radicals, as are found in most lipid acyl chains, recombine rapidly (2k = 10 -10 M s ) (192, 362) to form a variety of products, including alcohols and ketones (Reaction 67) (361, 362, 366), ketones and alkanes (Reaction 68) (60, 292), or acyl peroxides and peroxyl radicals (Reaction 69) (264, 367, 369). The alcohols thus produced are indistinguishable from H abstraction products of an original LO, but the ketones and dialkyl peroxides are unique to recombination reactions. As any R3OO and RO released from Reaction 68 or Reaction 69a react further, peroxyl radical recombinations also have the potential for propagating lipid oxidation (Section 3.1.4). 

Gortzi O, Papadimitriou E, Antimisiaris SG, loannou PV (2003) Cytotoxicity of arsono-lipid containing liposomes towards cancer and normal cells in culture effect of arsono-lipid acyl chain length. Eur J Pharm Sci 18 175-183... 

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