Figure 1.

(A) Sodium-dependent d-[³H]aspartate uptake in HeLa cells expressing wild-type and mutant transporters. Values are the average ± SEM of triplicate determinations. (B) Sodium-dependent uptake of d-[³H]aspartate in proteoliposomes prepared from HeLa cells expressing wild-type (⧫) and mutant transporters. The following mutant GLT-1 transporters were tested: T400S, •; A401C, ○; L402M, ▴; Y403F or E404D, ▵ (the same symbol is used for both because the values are superimposable); A405C, ▿; V406C, ▪; A407C, □. The medium contained 0.12 M potassium phosphate (pH 7.4). The protein concentration was in all cases around 1 mg/ml; data are expressed as pmol/mg of protein to normalize for the small variations in protein content resulting from individual reconstitutions. Reactions were stopped at the indicated times.