Fig. 2.
Inhibitor sensitivity of proline uptake in HP-21 cells. Inhibitor potencies were estimated in 50 nm[3H]-PRO in standard transport assays that were conducted with various concentrations (in moles per liter) of transport inhibitors and/or substrate. The data are expressed as a percentage of PRO accumulated in the absence of antagonist. The data were fit to a two-parameter expression: the percentage of PRO transport remaining is equal to 100/(1 + (IC50/[I])n), where IC50 is the concentration of competitor giving 50% of inhibition, [I] is the inhibitor concentration, andn is the Hill coefficient. IC50 values were converted to Ki values by using the Cheng and Prusoff (1973) correction for substrate concentration. Using this analysis, we calculated the following Kivalues (in μm): GGFL, 3.51; YGGFL, 9.44; proline, 16.1; pipecolic acid, 17.44. These data are the average ± SEM of two experiments performed in triplicate.