Different membrane lipid distribution between parental FEMX-I cells and prom1-exo. An automated ESI-tandem mass spectrometry approach was used. The lipid extracts from cells and microvesicles were dissolved in 1 ml chloroform. An aliquot of 50 μl of each extract in chloroform was used for each analysis. To correct for chemical or instrumental noise in the samples, the molar amount of each lipid metabolite detected in the “internal standards only” spectra was subtracted from the molar amount of each metabolite calculated in each set of sample spectra. The data from each “internal standards only” set of spectra was used to correct the data from the following 10 samples. Finally, the data were corrected for the fraction of the sample analyzed and normalized to the mg protein to produce data in the units nmol/mg. Data are presented as percent of total lipids analyzed. *, p < 0.05; **, p < 0.01 (unpaired Student’s t test). SM-DSM, sphingomyelin-dihydro sphingomyelin; PS, phosphatidylserine; PG, phosphatidylglycerol; e-PE, ether-linked phosphatidylethanolamine; e-PC, ether-linked phosphatidylcholine; PI, phosphatidylinositol; PA, phosphatidic acid.