Fitted parameters of L-Asp uptake by WT Glt _Ph in the presence of various anions. (a) Aspartate transport of Glt_Ph (C321A/N378C) was measured using the single-transporter FRET-based assay in NaNO₃ (blue) or Na-gluconate (red). Data are means and SE from three independent experiments performed as in Fig. 2 f. (b) Data in a and Fig. 2 f were fitted to triexponential functions (a three-phase association model; GraphPad Prism). Initial and final fractions of total possible uptake were set to 0 and 1, respectively. The three turnover rates (fast, intermediate, and slow), corresponding to the heterogeneous transporter populations, were constrained to be the same for all datasets (see Materials and methods for a detailed description of data processing). Three independent experiments per condition were analyzed, and values shown are means and SEM of the fitted parameters.