FIGURE 5.

Kinetics of amino acid influx into phosphatidylcholine liposomes. Using scintillation counting of liposomes: (A) representative [³H]Trp experiment at 4°C showing convergence (inset) and slope proportional to rate, k; cpm_t = cpm∞(1-e^-kt); (B) average of seven rate constants with SEM bars for tryptophan; (C) average of five rate constants with SEM bars for histidine; (D) average of three rate constants with SEM bars for isoleucine. Using optical techniques: (E) liposomal entry of tryptophan measured by Trp →NBD-PE FRET at 4°C showing convergence (inset) and slope proportional to rate. (F) Average of three FRET Trp uptake experiments with SEM bars.