1. Membrane Transport Group, Biozentrum, Martin-Luther-University Halle-Wittenberg, D-06120 Halle, Germany
2. Institute of Food Chemistry, Technische Universität Dresden, D-01062 Dresden, Germany
3. Julius-Bernstein-Institute for Physiology, Martin-Luther-University Halle-Wittenberg, D-06097 Halle, Germany