title: The effect of chemical modification of Saccharomyces cerevisiae on electrophoretic mobility, cell-wall structure and amphotericin B uptake.
abstract: Saccharomyces cerevisiae NCYC 239 suspended in solutions of NaCl showed two distinct plateaus in plots of electrophoretic mobility vs. pH, corresponding to pKa values of approx. 2 and 5. This is in contrast to cells suspended in buffer where only a single pKa (4) can be determined. Modification of cells with KI/I2 or nitrous acid led to altered electrophoretic mobility, indicating the presence of sulphydryl and amino groups, respectively, in the yeast cell surface, whereas uranyl nitrate modification had little effect, suggesting phosphate groups to be absent. Electron micrographs showed visible effects of KI/I2 and nitrous acid modification on cell membrane structure, and in these modified cells amphotericin B uptake was rapid. It is suggested that diffusion through the cell wall is the rate-limiting step for amphotericin B uptake. An activation energy of 20 kJ X mol-1 was determined for uptake of amphotericin B by unmodified cells.
mesh_terms: D000666:Amphotericin B / Q000378:metabolism*; D002473:Cell Wall / Q000648:ultrastructure; D055598:Chemical Phenomena; D002621:Chemistry; D004586:Electrophoresis; D005614:Freeze Fracturing; D006863:Hydrogen-Ion Concentration; D007455:Iodine / Q000494:pharmacology*; D008854:Microscopy, Electron; D009573:Nitrites / Q000494:pharmacology*; D009608:Nitrous Acid / Q000494:pharmacology*; D011193:Potassium Iodide / Q000494:pharmacology*; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D013816:Thermodynamics; D014502:Uranyl Nitrate / Q000494:pharmacology
chemical_list: D009573:Nitrites; D014502:Uranyl Nitrate; D011193:Potassium Iodide; D000666:Amphotericin B; D007455:Iodine; D009608:Nitrous Acid