Long-term stability of LeuT solubilized in DDM or a novel detergent (PSA-C10, PSA-C11, PSE-C9, PSE-C11, or PSE-C13) at concentrations of CMC + 0.04 wt% (a) and CMC + 0.2 wt% (b). DDM-purified transporter was mixed with individual detergent-containing solutions and then incubated for 12 days at room temperature. LeuT activity was measured at regular intervals during the incubation, by radiolabeled ligand ([3H]-Leu) binding via scintillation proximity assay (SPA).