FIG. 4.

Hoechst 33342 transport in inside-out membrane vesicles of HorA-expressing cells and nonexpressing cells of L. lactis. Membrane vesicles prepared from HorA-expressing cells (H) and control cells (C) were diluted to a concentration of 0.5 mg of membrane protein/ml in buffer containing the ATP regenerating system (see Materials and Methods) and 0.4 μM of each of the ionophores valinomycin and nigericin to dissipate the membrane potential and transmembrane pH gradient, respectively. After incubation for 1 min at 20°C, 2.3 μM Hoechst 33342 was added to the assay mixture. At the arrow, 2 mM Mg-ATP or 2 mM Mg-ATPγS was added. Hoechst 33342 transport was measured at 20°C by fluorimetry.