Phase transitions as a function of osmotic pressure in Saccharomyces cerevisiae whole cells, membrane extracts and phospholipid mixtures

Abstract : Fourier Transform Infrared spectroscopy (FTIR) was used to determine the phase transition temperature of whole Saccharomyces cerevisiae W303-1 A cells as a function of Aw in binary water–glycerol media. A phase transition occurred at 12 °C in water, at 16.5 °C at Aw=0.75, and at 19.5 °C at Aw=0.65. The temperature ranges over which transition occurred increased with decreasing Aw. A total lipid extract of the plasma membranes isolated from S. cerevisiae cells was also studied, with a phase transition temperature determined at 20 °C in pure water and at 27 °C in binary water–glycerol solutions for both Aw levels tested. The pure phospholipids dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE) and three binary mixtures of these phospholipids (percentage molar mixtures of DMPC/DMPE of 90.5/9.5, 74.8/25.2, and 39.7/60.3) were studied. For DMPC, there was no influence of Aw on the phase transition temperature (always 23 °C). On the other hand, the phase transition temperature of DMPE increased with decreasing Aw for the three aqueous solutions tested (glycerol, sorbitol and sucrose), from 48 °C in water, to 64 °C for a solution at Aw=0.67. For the DMPC/DMPE mixtures, transitions were found intermediate between those of the two phospholipids, and a cooperative state was observed between species at the gel and at the fluid phases.
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Céline Laroche, Hélène Simonin, Laurent Beney, Patrick Gervais. Phase transitions as a function of osmotic pressure in Saccharomyces cerevisiae whole cells, membrane extracts and phospholipid mixtures. Biochimica et Biophysica Acta:Biomembranes, Elsevier, 2005, 1669 (1), pp.8-16. ⟨10.1016/j.bbamem.2005.01.007⟩. ⟨hal-02292230⟩

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