FIGURE 9.

Cation competition. On a time trace at λ_Ex 290 nm and λ_Em 500 nm with SLM-8100/DMX fluorescence spectrophotometer, RSO containing MelB-ST was incubated with 5.6 mm Li⁺ (5-fold K_0.5) after the addition of 10 μm D²G and followed by a saturated concentration of either Li⁺ (40 mm, green curve) or Na⁺ (44 mm, red curve) as the arrows indicate. As a control, Na⁺ (44 mm) was directly added without Li⁺ (blue curve). The FRET signals are displaced with 130 mm melibiose. A.U., absorbance units.