Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis of archaebacterial lipids in lyophilized membranes dry mixed with 9-aminoacridine

A method of direct lipid analysis by MALDI mass spectrometry in intact membranes, without prior extraction/separation steps, is described. The purple membrane isolated from the extremely halophilic archaeon Halobacterium salinarum was selected as model membrane. Lyophilized purple membranes were grinded with 9-aminoacridine as dry matrix and the powder mixture crushed in a mechanical die press to form a thin pellet; small pieces of the pellet were then attached to the MALDI target and directly analyzed. In parallel, individual archaebacterial phospholipids and glycolipids together with the total lipid extract of the purple membranes were also analyzed by MALDI-TOF/MS, by using 9-aminoacridine as matrix in solution. Results show that 9-aminoacridine represents a suitable matrix for the conventional MALDI-TOF/MS analyses of lipid extracts from archaeal microorganisms as well as for fast and reliable direct dry lipid analyses of lyophilized archaebacterial membranes. This method might be of general application offering the advantage to quickly gain information on lipid components without disrupting or altering the membrane matrix. Supplementary key words: archaebacterial lipids, glycerolipids (diphytanylglycerol ether analogues), glycerophospholipids (diphytanylglycerolphosphate ether analogues), Halobacterium salinarum, purple membrane, MALDI-TOF/MS, 9-aminoacridine.