Effect of 1-palmitoyl lysophosphatidylcholine on phase properties of 1,2-dipalmitoyl phosphatidylethanolamine: A thermodynamic and NMR study
Biophysics; Biochemistry & Molecular Biology; cholesterol; fusion; lysolecithin; lipid; membranes; bilayer; H-2-NMR; transition; nuclear-magnetic-resonance; phosphatidylcholine vesicles; lecithin; bilayers; DSC; mixtures; P-31-NMR; phosphatidylethanolamine
The effect of 1-palmitoyl lysophosphatidylcholine (PLPC) on the phase behaviour of 1,2-dipalmitoyl phosphatidylethanolamine (DPPE) in excess water (34 wt%) has been examined by differential scanning calorimetry, scanning dilatometry and isothermal compressibility measurements. Mole percentages of PLPC in DPPE between 14 and 62% have been studied over the temperature range 30-75 degrees C. The temperature dependence of orientational ordering at selected sites in H-2-labelled PLPC and 2H(2)O has been determined from measurement of time-averaged chemical shift anisotropies and quadrupole splittings in the P-31- and H-2-NMR spectra. These data have been used to further characterize phase behaviour. At less than equimolar contents of PLPC, when a single phase transition with a reduced transition temperature is observed, spectral and calorimetric data indicate complete miscibility of the two lipid components. An equimolar mixture of PLPC and DPPE shows a sharp first order transition at 47.3 degrees C and a second order transition at 62.5 degrees C. NMR data are consistent with the existence of a defective bilayer at intermediary temperatures. In this range it is proposed that PLPC molecules prefer regions with high curvature in the vicinity of the defects, while DPPE molecules are mostly confined to flatter regions of the bilayer. A possible molecular model is described, At temperatures above 62.5 degrees C, PLPC and DPPE are completely miscible and exist as lamellae. At higher PLPC content (> 50 mol%), thermodynamic and spectral data are indicative of phase separation of the two components over the temperature range examined.
Checchetti A; Golemme A; Chidichimo G; LaRosa C; Grasso D; Westerman P W
Chemistry and Physics of Lipids
1996
1996-08
Journal Article or Conference Abstract Publication
<a href="http://doi.org/10.1016/0009-3084(96)02574-1" target="_blank" rel="noreferrer noopener">10.1016/0009-3084(96)02574-1</a>
Fluorescence Study Of A Temperature-induced Conversion From The Loose To The Tight-binding Form Of Membrane-bound Cytochrome-b5
bilayers; Biochemistry & Molecular Biology; cross-linking; decay; domain; embedded segment; orientation; photoactivatable phospholipids; topography; vesicles
Cytochrome b5 is a liver integral membrane protein that has now been expressed in, and isolated from, Escherichia coli. The structure-function relationships of the 43 amino acid membrane-binding domain (nonpolar peptide) have been examined in both native and mutant forms of the protein; in the latter, tryptophan residues at positions 108 and 112 were replaced by leucine. The temperature dependence of the fluorescence quantum yield of the Trp residues in the isolated membrane-binding domain was examined while the domain was bound to lipid vesicles. Both the lipid-bound mutant domain and lipid-bound native domain showed an irreversible increase in fluorescence above 50-degrees-C. When the whole cytochrome b5 molecule, bound to lipid vesicles, was heated to this temperature, there was a conversion of the metastable, intermembrane-exchangeable (''loosely'' bound), conformation to a final, virtually unexchangeable (''tightly'' bound), conformation. It has been suggested previously that the protein exists in a ''looped back'' conformation and a ''bilayer penetrating'' conformation. Although the present studies are not designed to determine the absolute conformations of the loose and tight forms, the changes observed in steady-state and frequency-modulated fluorescence and the lack of change in depth of Trp 109 in the bilayer are consistent with a movement of the C-terminal segment from a looped back to a bilayer penetrating conformation as the tight form is generated.
Ladokhin A S; Wang L; Steggles A W; Malak H; Holloway P W
Biochemistry
1993
1993-07
Journal Article or Conference Abstract Publication
<a href="http://doi.org/10.1021/bi00078a020" target="_blank" rel="noreferrer noopener">10.1021/bi00078a020</a>