Figure 4. Functional characteristics of CAT8 in yeast and oocytes.

(A) Uptake rates in 22Δ8AA yeast with 1 mM Gln. White bars: pH 5.5, black bars pH 7.5 (n = 4). The uptake by CAT8 was marginally significant at the p<0.05 level at pH 7.5 (*), using the Mann-Whitney test. (B) Uptake rates in oocytes at 1 mM Gln at pH 5.5 and pH 7.5. In the indicated experiments, Arg and Leu, or Glu and Phe, were added at 2 mM as competitors (n = 3).The uptake by CAT8 was significant at the p<0.05 level (Mann-Whitney test). (C) Concentration dependence of Gln uptake by CAT8. Uptake from water-injected oocytes was subtracted from CAT8-injected oocytes at pH 7.5. A linear background uptake was observed in both oocyte batches. (D) Current-voltage relations of CAT8-expressing oocytes in the absence (black circle) and presence (open triangle) of 1 mM Gln at pH 5.5 (n = 4, solid lines). The dashed line corresponds to the current-voltage relation of water-injected control oocytes from the same batch (closed triangles). Similar data were obtained at pH 7.5.