An investigation was made into the effect of enrichment of the plasma membrane of Saccharomyces cerevisiae NCYC 366, with either phosphatidylcholine or phosphatidylethanolamine, on the susceptibility to surfactants. The three surfactants used were cetyltrimethyl-ammonium bromide, sodium dodecyl sulphate and Triton X-100. There was no difference in the loss of viability or release of cations between populations of the two types of enriched cells when suspended in buffered cetyltrimethylammonium bromide. However, populations of cells with plasma membranes enriched in phosphatidylethanolamine lost viability and cations at a greater rate when suspended in buffered sodium dodecyl sulphate. Although Triton X-100 possessed little antimicrobial activity, it was able to induce a similar release of cations from populations of cells enriched in either phosphatidylcholine or phosphatidylethanolamine suspended in buffered 1.2 M-sorbitol. No difference was found in the ability of cetyltrimethylammonium bromide or Triton X-100 to induce release of cations, in buffered 1.2M-sorbitol from sphaeroplasts prepared from cells enriched in eitherphospholipid, but sphaeroplasts from cells enriched in phosphatidylcholine released cations faster when suspended in buffered sorbitol containing sodium dodecyl sulphate. Liposomes containing potassium chloride prepared from mixtures of phospholipids extracted from cells enriched in either phosphatidylcholine or phosphatidylethanolamine lost potassium ions at the same rate when challenged with either sodium dodecyl sulphate or Triton X-100 but no release of potassium ions was detected when they were challenged with cetyl-trimethylammonium bromide. Cells and sphaeroplasts enriched in phosphatidylcholine or phosphatidylethanolamine did not differ in appearance in scanning or transmission electron micrographs. There were no differences between the two types of enriched cells, in electrophoretic mobilities over a pH range 2 to 9, in ease with which they were converted into sphaeroplasts with beta-glucanase, or in the permeability to a range of probing molecules. Walls from phosphatidylcholine- and phosphatidylethanolamine- enriched cells had similar contents of beta-glucans, alpha-mannan and protein. A time-course study was made of sphaeroplast formation, using cells that were not enriched in either phosphatidylcholine or phosphatidylethanolamine, employing the electron microscope. The mode of action of the three surfactants is discussed, in particular the possible reasons for the different sensitivities of cells and sphaeroplasts enriched with either phosphatidylcholine or phosphatidylethanolamine to sodium dodecyl sulphate. There is also a discussion on some aspects of the cell wall and sphaeroplasts as revealed by electron microscopy.
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