Figure 4.

Uptake kinetics studies of PNA_TAR–penetratin, PNA_TAR–tat-peptide, PNA_TAR–transportan-21 and PNA_TAR–transportan-22 in CEM cells. The ¹²⁵I-labeled conjugate was incubated with CEM cells and the amount of conjugate taken up by the cells was determined from specific radioactivity of the conjugate as described in the Materials and Methods. The uptake of the conjugate was plotted against the log of conjugate concentration and the cooperativity index ([S]_0.9/[S] _0.1) was determined (left panels). Hill coefficient (nH) was determined from the slope of the Hill plot of the uptake data shown in the right panels. Cooperativity index represents the ratio of the substrate at 0.9 V_max and 0.1 V_max while nH represents the concentration of the conjugate at which the velocity of the uptake is equal to 0.5 V_max. PNA_TAR–transportan data (24) were provided for comparison.