title: Tetraphenylphosphonium ion is a true indicator of negative plasma-membrane potential in the yeast Rhodotorula glutinis. Experiments under osmotic stress and at low external pH values.
abstract: In the yeast Rhodotorula glutinis, accumulation of the tetraphenylphosphonium ion (TPP+) was increased under conditions of osmotic stress, indicating a hyperpolarization of the negative membrane potential (delta psi). The following observations were consistent with the occurrence of hyperpolarized delta psi: enhanced accumulation of glucosamine, the uptake of which is also driven by delta psi; increased respiratory rate. The accumulation of TPP+ was gradually decreased by lowering the pH of cell suspensions. At pH values below 4.5, no TPP+ was taken up, but instead thiocyanate (SCN-) was accumulated, indicating a positive delta psi. The pH-dependent influx of glucosamine followed the pattern of TPP+ accumulation both in the wild-type and in the nystatin-resistant mutant, M67, which displayed a negative delta psi down to pH 3. Thus TPP+ accumulation in Rh. glutinis reflected actual electrical potential difference across the plasma membrane.
mesh_terms: D005944:Glucosamine / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007202:Indicators and Reagents; D008564:Membrane Potentials / Q000187:drug effects; D003904:Mitosporic Fungi / Q000502:physiology*; D009761:Nystatin / Q000494:pharmacology; D009861:Onium Compounds; D009943:Organophosphorus Compounds; D009997:Osmotic Pressure; D010101:Oxygen Consumption; D010429:Pentoses / Q000494:pharmacology; D012248:Rhodotorula / Q000187:drug effects / Q000502:physiology*
chemical_list: D007202:Indicators and Reagents; D009861:Onium Compounds; D009943:Organophosphorus Compounds; D010429:Pentoses; D009761:Nystatin; D005944:Glucosamine; C013289:tetraphenylphosphonium