Flow microcalorimetric study of the effects of pH, metal ions and sterols on the interaction of polyene antibiotics with Saccharomyces cerevisiae NCYC239.

The effects of pH, metal ions (calcium and magnesium) and sterols (cholesterol and ergosterol), on the interaction of polyene antibiotics with respiring Saccharomyces cerevisiae (NCYC 239) cells have been studied by flow microcalorimetry. The bioactivity of nystatin decreases as the pH of the medium increases toward neutral. Calcium and magnesium ions attenuate the biological effects of nystatin, amphotericin B and candicidin. The activities of filipin and pimaracin (natamycin) are unaffected by the presence of these ions. Ergosterol and cholesterol show similar effects. Some possible explanations for these observations are suggested.