Acyl chain order

For comparison, 2-parinaroyl-phosphatidylcholine (PPC) was also incorporated into the membrane preparations. For the Torpedo membranes, the acyl chain order measured by PPI was found to be lower than that by PPC, whereas the opposite was true for the vesicles. This inversion strongly suggests that PI has different interactions with certain membrane components compared to PC. In contrast, the correlation times of PPI and PPC were only slightly different in Torpedo membranes, and the values showed little difference with those measured in vesicles. 

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... 

Another subtlety in double bond chemistry that is important in determining the effects of double bonds on membrane structure is the position within the acyl chain at which double bonds are found. The introduction of a double bond near the center of the acyl chain, for instance at position 9 in the formation of oleic acid from stearic acid, has the largest effect on acyl chain order. Long-chain polyunsaturates with multiple double bonds have disordering influences that are highest near the membrane interior (Hazel et al., 1992). Cold acclimation is frequently characterized by the incorporation into phospholipids of long-chain polyunsaturates such as docosahexanoic (DHA) acid, a 22-carbon acid with six double bonds. 

Sinensky, M., F. Pinkerton, E. Sutherland, and F.R. Simon (1979). Rate limitation of (Na+-K+) ATPase by membrane acyl chain ordering. Proc. Natl. Acad. Sci. USA 76 4893 4897. 

The interaction of soluble cations with the phospholipid phosphate groups has been investigated on a mixture of DPPC and 1,2-dipalmitoyl-sn-glycero-3-phosphoserine DPPS as a function of surface pressure and Ca2+ ion presence [51], The presence of Ca2+ in the subphase induce an acyl chain ordering at all surface pressures in both components of the binary mixture that was not observed in the case of pure DPPC alone. Unlike the bulk phase mixture of... 

Figure 6 Results for lipid raft systems with varying amounts of POPC (palmitoyl-oleoyl-phosphatidylcholine), SM, and cholesterol (42), which shows plots for one leaflet from above. The top row for the system is a 1 1 1 mixture of POPC, SM, and cholesterol. The middle row shows data for Sg (2 1 1 for POPC SM cholesterol), and the bottom row shows data for Sq (62 1 1 for POPC SM cholesterol). The first column on the left shows data for the acyl chain order parameter (Sqq) averaged over selected carbons in POPC and SM chains. The second and third columns depict the in-plane electron densities of cholesterol and the selected chain carbons, respectively.

Schuler, I. A. Milon Y. Nakatani G. Ourisson A.M. Albrecht P. Benveniste M.A. Hartmann. Differential effects of plant sterols on water permeability and on acyl chain ordering of soybean phosphatidylcholine bilayers. Proc. Natl Acad. Sci. USA, 1991, 88, 6926-6930. 

Researchers have studied whether acyl-chain order could be responsible for the preferred sterol interaction with SMs. Acyl-chain order was deduced from diphenylhexatriene anisotropy and from the deuterium order parameter obtained by H-NMR on bilayers made from either 14 0/14 0(d27)-PC, or 14 0(d27)-SM7 Some researcher analyzed the ground and excited states of phospholamban (PLN), a membrane protein that regulates sarcoplasmic reticulum (SR) calcium ATPase (SERCA), in dilferent membrane mimetic environments. Gustavsson et al. have previously proposed that the conformational equilibrium of PLN are central to SERCA regulation. They have now shown that these equilibrium detected in micelles and bicelles are also present in native sarcoplasmic reticulum lipid membranes as probed by MAS solid-state NMR. ... 

Likewise, the acyl chain order parameters of phos-phatidylethanolamines collectively decrease when going from the L to the Hu phase, due to the greater motional freedom of the chains in the inverted hexagonal structure [27,28,20]. Geometrical models have been recently proposed that relate chain order parameters with the cylinder curvature in a Hi.rphase [20,29]. It has been noted that similar considerations may not be valid for the Hi phase due to the possibility of chain backbending [20]. 

A. Fatty Acyl Chain Order in Saturated Lipid Membranes... 

---