TABLE 1

Apparent inhibition constants and PEPT1- as well as PEPT2-mediated currents of various thiazolidide-derivatives with varying N-terminal amino acid residues

The concentration dependence of the different thiazolidide-derivatives for inhibition of uptake of d-Phe-Ala in PEPT1- and PEPT2-expressing P. pastoris yeast cells was measured after 15-min incubation in presence of varying concentrations (0-20 mM) of competitor at pH 6.5. Apparent EC₅₀ values ± S.E. were calculated by nonlinear regression analysis. Values represent the mean of at least two different uptakes. In the last two columns is shown the ability of the Thia-derivatives to serve as substrates for either PEPT1 or PEPT2. This was determined by applying the two-electrode voltage-clamp technique with X. laevis oocytes expressing the respective transporter. Data represent the normalized currents of the selected compounds (5 mM) relative to the glycyl-glutamine (5 mM)-evoked currents at pH 6.5 at a membrane potential of −60 mV. I_{5 mM} values of compounds not significantly higher than background values in water-injected oocytes (P > 0.05, Student's paired t test) are given as 0.