Figure 3.

Expression of bovine LAT in Xenopus laevis oocytes. Oocytes were injected with 50 nl water or cRNA solution containing 80 ng of bovine LAT and/or 10 ng of rat 4F2hc and incubated for 4 days at 18°C. (A) The volume of distribution (V_D) of [³H]tryptophan in oocytes is increased after the coinjection of 4F2hc mRNA and bovine LAT mRNA. (B) Inhibition of bovine LAT-mediated [³H]tryptophan uptake by amino acids added in 500 μM concentrations. BCH, 2-aminobicyclo[2.2.1]heptane-2-carboxylic acid; MeAIB, N-methylaminoisobutyric acid. (C) Kinetic analysis of the LAT-mediated uptake of [³H]tryptophan. Oocytes were injected with 4F2hc cRNA alone (♦, ▴ in Inset) or in combination with bovine LAT (■). Competition studies were performed by varying the concentration of [³H]tryptophan (14–140 nM) or by increasing the levels of unlabeled tryptophan (0.3–500 μM). The Inset represents the beginning of the curve shown in the main figure, and it is used to demonstrate that there are no changes in K_m. Each bar or point represents mean ± SE, n = 5.