Composition and phase behaviour of polar lipids isolated from Spirulina maxima cells grown in a perdeuterated medium

The lipid composition of Spirulina maxima cells grown in a perdeuterated medium was determined by using nuclear magnetic resonance spectroscopy, fast atom-bombardment-mass spectrometry, gas chromatography-mass spectrometry as well as conventional chemical methods. The extent of deuteration was determined by mass spectrometry and was superior to 97.5%. The major lipids identified in the strain were: non-polar lipids (9%), monogalactosyldiacylglycerol (5%), digalactosyldiacylglycerol (22%), phosphatidylglycerol (31%), sulfoquinovosyldiacylglycerol (32%), phosphatidylinositol (traces). The major fatty acids were 16:0 (80%) and 18:1 (15%). These results demonstrate that the adaptation of the cells to D2O did not imply a profound modification of the lipid composition. The perdeuterated polar lipid mixture dispersed into an excess of water organises spontaneously in a lamellar phase as seen by 31P and deuterium solid state NMR and can therefore be used to prepare perdeuterated model membranes with a well defined composition. Liposomes made using these lipids have a gel to liquid-crystalline phase transition in the range 15-27 degrees C and are in a fluid L alpha phase above this temperature.