Nucleoside Transport. II. Inhibition by p-Nitrobenzylthioguanosine and Related Compounds

p-Nitrobenzylthioguanosine (NBTGR) was found to be a potent inhibitor of nucleoside transport by human erythrocytes; initial rates of uridine uptake were reduced to zero upon exposure of cells to 10−6 M NBTGR. The inhibitor was firmly bound because repeated washing did not restore uridine transport capability to NBTGR-treated cells. NBTGR inhibited the influx of uridine, inosine, and cytidine, without inhibiting the uptake of the corresponding bases, or that of D-glucose or L-leucine. Uridine antagonized the NBTGR inhibition of uridine transport in a concentration-dependent manner. NBTGR and related compounds appear to interact with the mechanism for the facilitated transport of nucleosides.