Plasma membranes isolated from HeLa cells cultivated in suspension cultures supplemented with 3.5% fetal bovine serum or 2% of the commercially available serum substitute Ultroser G contained the same amounts of protein, cholesterol, and phosphate on a cellular basis. Minor differences in the plasma membrane fatty acid composition were seen, with the most pronounced alteration observed for palmitic acid, which amounted to 27 and 20% in fetal bovine serum- and Ultroser G- supplemented cells, respectively. Plasma membranes from cells grown with Ultroser G contained almost twice as much phosphatidylethanolamine and displayed two thirds of the phosphatidylcholine content, compared to plasma membranes obtained from fetal bovine serum supplemented cells. The former membranes also showed a 3 times higher specific [3H]acetate labeling of cholesterol, indicating a higher de novo synthesis of cholesterol. Both quantitative and qualitative alterations were revealed among the plasma membrane polypeptides when these were subjected to immuno- and lectin blottings. Fluorescence anisotropy measurements at different temperatures produced similar results irrespective of the growth medium supplement when the plasma membrane specific probe 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene was used on intact cells. However, the average cellular rigidity was higher for Ultroser G supplemented cells, determined with 1,6-diphenyl-1,3,5-hexatriene as a probe.
Class separation of common glycerolipids on a diol‐phase liquid chromatography column with a gradient of the mixed solvents hexane/isopropanol/acetic acid/triethylamine is compatible with on‐line plasmaspray ionization mass spectrometry. The positive ion mass spectra exhibit prominent diacylglycerol and monoacylglycerol derived fragments, which can be utilized for quantification. In the selected‐ion monitoring mode, the detection limit for phospholipids is in the low nanogram range. The abundance of the diacylglycerol and monoacylglycerol fragments reflects the relative fatty acid composition of the phospholipid classes. Collision‐induced decomposition of diacylglycerol fragments with argon as collision gas unambiguously reveals the chain length and degree of unsaturation of the esterified fatty acids in the native lipid.
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