The rate of uptake of ThDP at submicromolar concentrations by mitochondria from normal lymphoblasts. Mitochondria were isolated from normal lymphoblasts and were incubated for 15 minutes with various concentrations of radioactive ThDP in the absence (open squares) or presence (open circles) of 30 μM nonradioactive ThDP. Mitochondrial-associated counts were determined, and the velocity (V) (pmol ThDP per mg mitochondrial protein 15 min.) is plotted versus the concentration in micromolar of radioactive ThDP ([S]). The calculated V versus [S] for the low affinity component only, using the kinetic parameters for that component, also is plotted (open triangles). Error bars represent ± SEM for four independent experiments in the absence and three experiments in the presence of non-radioactive ThDP.