Efflux System for Pyridoxine in Schizosaccharomyces pombe

Abstract

  Pyridoxine-charged Schizosaccharomyces pombe released pyridoxine rapidly at 30°C: very low amounts of three other B₆ vitamers were also released. The rate of efflux was temperature-dependent. The initial rate of efflux was dependent on the concentration of pyridoxine in the cells: the rate was almost zero at lower than 0.02 mM and became saturated at higher than 0.2 mM. Na⁺, sodium azide, and dinitrophenol increased the rate in both the presence and absence of D-glucose. Mg⁺⁺, thiamine, and menadione inhibited the efflux. The intracellular concentration of ATP did not significantly affect the efflux rate. The system may be dependent on a membrane potential of the yeast cells. It was found that the fission yeast cells have a gate or carrier system for efflux of pyridoxine, which was distinct from that in Saccharomyces cerevisiae.