Intracellular pH-dependent efflux of the fluorescent probe pyranine in theyeast Yarrowia lipolytica

8-Hydroxypyrene-1,3,6-trisulfonic acid (pyranine) can be used as a vital in tracellular pH (pH(i)) indicator. In the yeast Yarrowia lipolytica, a parti al efflux of the probe was detected by using the pH-independent wavelength of 415 nm. A simplified correction of the fluorescent signals was applied. enabling to show for this species a good near-neutral pH(i) maintenance cap acity in a pH 3.9 medium. Octanoic acid. which is known to have toxic effec ts on yeast, decreased the pH(i) and increased the 260-nm-absorbing compoun ds leakage. However, this acid inhibited the fluorescent probe efflux linea rly with its concentration suggesting a pH(i)-dependent efflux of pyranine from cells. (C) 2001 Federation of European Microbiological Societies. Publ ished by Elsevier Science B.V. All rights reserved.