With our optimized transport conditions, we tested whether we could transport most transporter molecules from the sender to the receiver phase. We used 10 mM Cbz-D in the sender phase, with a 113 mm 2 interface area, stirred at 1000 rpm. We fueled the sender phase with 100, 200, 300, or 400 mM EDC. In contrast to the experiments with the large sender lengths, we found that the transport efficiency plateaued and even decreased with increasing fuel (Fig. ). We explain the loss in efficiency as follows: the additional fuel does not proportionally activate more transporter molecules. For example, with 100 mM EDC, the maximum concentration activated Cbz-D peaks at roughly 2.5 mM within the first minutes, whereas with 400 mM, it peaks at 6 mM (Fig. ).