title: Nucleoside transport in human and sheep erythrocytes. Evidence that nitrobenzylthioinosine binds specifically to functional nucleoside-transport sites.
abstract: Nitrobenzyl[35S]thioinosine binding and nitro[3H]benzylthioinosine binding to nucleoside-permeable and nucleoside-impermeable sheep erythrocyte membranes was investigated, and compared with that found for human erythrocytes. High-affinity nitrobenzylthioinosine-binding sites (apparent KD congruent to 1 nM) were present on human and nucleoside-permeable but not nucleoside-impermeable sheep erythrocyte membranes (8400 and 18 sites/cell for human and sheep nucleoside-permeable sheep erythrocytes was displaced by nitrobenzylthioguanosine and dipyridamole. Uridine, inosine and adenosine inhibited binding. The smaller number of nitrobenzylthioinosine sites on nucleoside-permeable cells compared with human erythrocytes corresponded to a considerably lower Vmax. for uridine influx in these cells (0.53 X 10(-20) mol/cell per s at 25 degrees C compared with 254 X 10(-20) mol/cell per s). It is suggested that high-affinity nitrobenzylthioinosine binding represents a specific interaction with functional nucleoside-transport sites. The uridine-translocation capacity for each transport site at 25 degrees C is 180 molecules/site per s for both nucleoside-permeable sheep cells and human erythrocytes (assuming a 1:1 interaction between nitrobenzylthioinosine and the nucleoside-transport system).
mesh_terms: D000818:Animals; D001665:Binding Sites; D001692:Biological Transport / Q000187:drug effects; D002463:Cell Membrane Permeability; D004910:Erythrocyte Membrane / Q000187:drug effects / Q000378:metabolism*; D004912:Erythrocytes / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D007288:Inosine / Q000031:analogs & derivatives; D007700:Kinetics; D009578:Nitrobenzenes; D009705:Nucleosides / Q000097:blood* / Q000494:pharmacology; D012756:Sheep; D013868:Thioinosine; D014529:Uridine / Q000097:blood
chemical_list: D009578:Nitrobenzenes; D009705:Nucleosides; D013868:Thioinosine; D007288:Inosine; D014529:Uridine