Table 2. Comparison of endogenous Xenopus laevis L-leucine transporter maximum turnover rates estimated using model input data from assays in various combinations of uptake buffers.

	Original	Test
Experimental buffer conditions used as model input	Leu+Na+Leu+Na+free	Leu+Na++Ala+Arg Leu+Na++BCH	Leu+Na++BCHLeu+Na+free+Ala	Leu+Na++Ala+ArgLeu+Na++BCHLeu+Na++BCH+Ala	Leu+Na+Leu+Na++Ala+ArgLeu+Na+freeLeu+Na+free+Ala
Vmax,xB0AT1	30.7 ± 5.1	28.2 ± 8.1	39.2 ± 4.3	27.9 ± 4.8	34.3 ± 2.5
Vmax,xLAT4	383.4 ± 8.7	405.3 ± 16.6	372.1 ± 8.2	406.5 ± 9.4	382.0 ± 3.2

Results are amino acid transporter maximum transport rates (normalized to uptake rate at 1 mM Leu in +Na⁺ buffer) with standard deviations (V_max,i ± SD). The model estimations were calculated using data generated from different combinations of uptake buffers as indicated in the column headings. Data generated from assays in the “Original” buffer combination was used for model estimations of Vmax. The dependence of the model calculations on the data from different buffer combinations used as input was probed using the “Test” buffer combinations. The mean V_max,i ±SEM for the four “Test” buffer combinations is 32.4 ± 2.7 for xB⁰AT1 and 391.5 ± 5.2 for xLAT4.