X-ray diffraction demonstrates that phosphatidyldiacylglycerol and phosphatidylcholesterol are not lamellar above the...

X-ray diffraction was used to investigate the lattice structure of aqueous dispersions of two phosphatidyldiacylglycerols and of a phosphatidylcholesterol above and below the chain melting transition temperature. Previously, Noggle et al. (Biochim. Biophys. Acta (1982) 691, 240-248) had investigated these lipids and had concluded on the basis of electron microscopy that the lipids were in a lamellar state above the transition temperature. However, they found the 31P-NMR signals were not characteristic of lamellar phases. It was, therefore, concluded that these lipids were yielding unexpected 31P-NMR spectra. The present X-ray results demonstrate that, in fact, the lipids are not in a lamellar state above the transition temperature and that the 31P-NMR and X-ray data are not necessarily in disagreement. Characteristics of the phases both above and below the chain melt temperature are discussed.