| Abstract
| - 1,2-Dimyristoyl-sn-glycero-3-phospho-rac-glycerol has been suggested to form at intermediate temperatures andat high concentrations in low-salt solutions as a continuous sponge phase (Heimburg, T.; Biltonen, R. L. Biochemistry1994, 33, 9477−9488). In the present study, the changes in signals seen for a range of fluorescent probes during phasetransformations of this phospholipid indicate continuous melting and a change in lipid packing, in accordance withprevious reports. However, in accordance with Lamy-Freund and Riske (Lamy-Freund, M. T.; Riske, K. A. Chem.Phys. Lipids2003, 122, 19−32), no enhancement of lipid mixing within the putative sponge phase region was seen,suggesting a lack of a connected lipid surface. Accordingly, a typical sponge phase cannot account for the propertiesof the intermediate phase. The low scattering intensities of the latter have also been taken as evidence for disaggregation.While dynamic light scattering and data for membranes containing poly(ethylene glycol)-ylated lipids could lendcredence to disaggregation, the most likely explanation for the scattering data would appear to be a shape transitionwithout significant changes in neither vesicle aggregation nor bilayer connectivity. An abrupt change in light scatteringand signals from some of the fluorescent probes used reveals a new transition at Tt ≈ 43 °C, with the formation ofa more ordered interface.
|
