Lipids alkylation

The most likely way for pardaxin molecules to insert across the membrane in an antiparallel manner is for them to form antiparallel aggregates on the membrane surface that then insert across the membrane. We developed a "raft"model (data not shown) that is similar to the channel model except that adjacent dimers are related to each other by a linear translation instead of a 60 rotation about a channel axis. All of the large hydrophobic side chains of the C-helices are on one side of the "raft" and all hydrophilic side chains are on the other side. We postulate that these "rafts" displace the lipid molecules on one side of the bilayer. When two or more "rafts" meet they can insert across the membrane to form a channel in a way that never exposes the hydrophilic side chains to the lipid alkyl chains. The conformational change from the "raft" to the channel structure primarily involves a pivoting motion about the "ridge" of side chains formed by Thr-17, Ala-21, Ala-25, and Ser-29. These small side chains present few steric barriers for the postulated conformational change. 

Figure 17.2 Lipid peroxidation scheme. LH, a polyunsaturated fatty acid LOOM, lipid hydroperoxide LOH, lipid alcohol L, lipid radical LOO, lipid hydroperoxyl radical LO, lipid alkoxyl radical. Initiation the LH hydrogen is abstracted by reactive oxygen (e.g. lipid alkyl radical, lipid alkoxy radical, lipid hydroperoxyl radical, hydroxy radical, etc.) to produce a new lipid alkyl radical, L. Propagation the lipid alkyl, alkoxyl or hydroperoxyl radical abstracts hydrogen from the neighbouring LH to generate a new L radical.

In the membrane lipid alkyl chains of n-SASL and n-PC spin labels undergo rapid rotational motion about the long axis of the spin label and wobble within the confines of a cone imposed by the... 

Abbreviations BSO, D.L-buthionine-. i -sulfoxime L , lipid alkyl radicals LH, lipid LO, Upid alkoxyl radicals LOO, Upid peroxyl radicals L-NAME, yV -nitro-L-arginine-methyl ester MBl, methylene bridge index (mean number of h -aUytic methylene positions per fatty add) NO, nitric oxide NOS, nitric oxide synthase NO, nitrite N02, nitrogen dioxide NO2CI, nitryl chloride O2 , superoxide OH, hydroxyl radical OL, epoxyaUyhc radical OLOO, epoxyperoxyl radical 0=NOO , peroxynitrite SNAP, S-nitroso-iV-acetyl-D.L-penicillamine SOD, superoxide dismutase contd. onp. 98, Subcellular Biochemistry, Volume 36 Phospholipid Metabolism in Apoptosis. 

L, LO, and LOO represent lipid alkyl, alkoxyl, and peroxyl radicals, respectively derived from lipid, LH, and lipid hydroperoxides, LOOH). 

Origin of DOM Number VM CHYDR PHLM LDIM LIPID ALKYL NCOMP STEROL PEPTI SUBER FATTY... 

Thus, the partial or total removal of the interdigitation of the lipid alkyl chains by cholesterol seems to be an important factor in determining the ability of the ketone molecule to place the C = O group close to the polar interface, at low temperatures. As the interdigitation is removed, the contact between the C = O group of the 9HP molecule and the solvent increases. 

The order parameters are mostly used to judge the correspondence of the obtained results to the experiment. Three different kinds of order parameters are used in the literature to characterize the conformational state of the lipid alkyl chains. The first is SCD, which can be obtained directly from the quadrupolar splitting of selectively deuterated phospholipids by NMR. SCD is related to the observed quadrupolar splitting by Eq. 6.5 ... 

Robinson et al. [69] studied the influence of cholesterol on molecular ordering of phospholipids by MD simulation. They used a more detailed description of the phospholipids including the head groups and charges. The simulated system contained two cholesterol molecules and 18 DMPC molecules in each leaflet of the bilayer (10 mol% cholesterol) and was simulated after equilibrium for 400 ps employing NVT conditions. They observed an increase in the fraction of trans conformations of the lipid alkyl chains with a decrease in kinks. Also, the dynamic and conformation of the flexible cholesterol side chains was characterized and it was found that they had a smaller tilt angle than the lipid chains with respect to the bilayer normal. 

Figure 5 Murine stratum comeum normal full thickness. Powder diffraction patterns obtained from mouse SC at 25°C. The upper figure shows the small-angle lamellar pattern produced by the intercellular lipid domains, with a repeat period of 131 2 A. The lower figure shows the wide-angle pattern produced by the lipid alkyl chains and the comeocyte envelope. See text. (Data from White et al., 1988.)...

The number density of DPPC molecules in OA/DPPC monolayers reflects the packing of lipid alkyl chains. It would be expected that if DPPC chains were packed similarly in the DPPC and DPPC/OA monolayers, then the number densities of the chains, after being corrected for the mole fraction of DPPC present, would be the same. However, it is apparent that at all surface coverages the number density of DPPC chains in the mixed monolayer is less than 50% of its value in the absence of OA. This indicates that there is increased free volume induced in the DPPC alkyl chains by OA. 

Wiesenthal T, Baekmark TR, Merkel R (1999) Direct evidence for a lipid alkyl chain orderng transition in poly(ethylene oxide) lipopolymer monolayers at the air-water interface obtained from infrared reflection absorption spectroscopy. Langmuir 15 6837-6844... 

Side chains in membrane proteins are inherently facing different types of environments the neighboring side chains of the protein, the bulk water, or the lipid alkyl chains. The protein topography with respect to the water and membrane interfaces is an important aspect in membrane protein studies and is not directly... 

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