Figure 7.

Transient concentration decrease during translocation. (A) Schematic of the dynamics of acceptor distribution during the translocation process. At positive potential (inside), the negatively charged acceptors are all in the inner leaflet (left). Once the potential reverses to negative, they exponentially relocate to the outer leaflet. At some time during the translocation process, the concentration on both sides is equal (center). Now the mean distance to the acceptor r(t) is 1.41 times longer than initially (inner leaflet). In the new steady state (right), all acceptors are in the outer leaflet, and the situation is inverted to the initial one. (B) Relation between energy transfer efficiency and distance between donor and acceptor. The distance is a function of the concentration of the acceptors in the membrane. Numbers indicate distances (and ET) at the initial state for the inner (1) and outer (2) leaflet, as well as at equal concentrations for both leaflets (3), assuming the concentration is such that the initial value of r(t) = R₀. The arrows indicate how the distance and ET change during a voltage pulse (dynamic fluorescence response) for the inner (solid) and outer (dashed) leaflet. dET indicates the difference in energy transfer for the donors in the inner leaflet between initial (1) and equal state (3). A positive transient is generated as a result of the change of ET between (1) and (3) being larger than between (2) and (3). (C) Variables used in formulas: d, thickness of the bilayer; r, distance between donor and acceptor; 2x, mean distance between two acceptors in one leaflet; p, fraction of the bilayer at which the fluorophore is located.