Fig. 4. Long-term activity of wild type leucine transporter (LeuT), ligand binding affinity and KI accessibility of the LeuT E192C^TMR. Long-term stability was measured by using the transporter solubilized in novel amphiphiles (TDT-C11, TDT-C12, NDT-C11 and NDT-C12) and a conventional detergent (DDM). The detergents were used at CMC + 0.04 wt% (a) and CMC + 0.2 wt% (b). Protein activity for LeuT was measured by scintillation proximity assay (SPA). Results are expressed as % activity relative to activity at day 0 (mean ± s.e.m., n = 2). (c) Saturation binding of [³H]leucine assessed by SPA for mutant protein, LeuT E192C^TMR, in either CMC + 0.04 wt% DDM or NDT-C11. Data are fitted to a single site model. Data points are means ± s.e.m. with n = 3–4. (d) K_SV values were plotted as a function of leucine concentration at CMC + 0.04 wt% detergent concentration. A conventional detergent (DDM), newly prepared NDT-11, and previously reported MNG-3 were used for comparison. Data points are means ± s.e.m. with n = 3–4.