engleski

Unusual lipid composition of the cell membranes of recycled brewer's yeast

The main lipids of the yeast membranes are phospholipids, ergosterol, and sphingolipids. Their composition is rigidly maintained during exponential growth under favourable conditions ; however, it alters markedly in response to extracellular changes. For that reason interest in yeasts has been renewed for their potential application in the production of highly specific fats. In that aim, lipid fraction of the plasma membrane and mitochondria of brewer^, s yeast obtained as by-product of malt fermentation during the anaerobic process of beer production was analysed. Major phospholipids in both organelles were phosphatidylcholine (PC), phosphatidylinositol (PI) and phosphatidylethanolamine (PE). In the plasma membrane PI was present in the highest concentration, while in the mitochondria it was PC, followed by PI. The main feature of the fatty acid composition of both organelles was high preponderance of saturated fatty acids, among which palmitic acid was the principal one. Both, the phospholipid and fatty acid compositions of the plasma membrane and mitochondria had some interesting features, but more or less easy to explain regarding the growth phase and conditions. High concentration of PI was found to be the characteristics of stationary growth phase, while high concentration of saturated fatty acids was the consequence of anaerobic conditions etc. On the other hand results of the analysis of neutral lipid composition were rather surprising. Squalene accounted for more than 30% of total cell lipids, which was three times more than ergosterol and may also be explained as the consequence of anaerobic growth conditions. Ergosterol was present in very low concentrations in both organelles, as well (12 and 7 microg/mg proteins, respectively), but squalene, which is, if at all, present only in trace amounts in the membranous systems, accounted for 25 and 22 microg/mg proteins, respectively. Such finding led us to the conclusion that recycled brewer^, s yeast grown in the anaerobic conditions, in the lack of ergosterol incorporates squalene in its membranes.

lipids; cell membrane; brewer's yeast

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