Passive and carrier-mediated permeation of different nucleosides through the reconstituted nucleoside transporter.
When reconstituted into proteoliposomes, the human erythrocyte nucleoside transporter catalysed nitrobenzylthioguanosine (NBTGR)-sensitive zero-trans influx of three different nucleosides at broadly similar rates (inosine, uridine greater than adenosine). However, proteoliposomes also exhibited high rates of NBTGR-insensitive uptake of adenosine, making this nucleoside unsuitable for reconstitution studies. Equivalent high rates of adenosine influx were observed in protein-free liposomes, establishing that this permeability pathway represents simple diffusion of nucleoside across the lipid bilayer. In contrast to adenosine, inosine and uridine exhibited acceptable rates of NBTGR-insensitive uptake. Of the two, inosine is the more attractive permeant for reconstitution experiments, having a 2.5-fold lower basal membrane permeability. Studies of nucleoside transport specificity in reconstituted membrane vesicles should take account of the widely different passive permeabilities of different nucleosides.
Tse
C M
CM
Department of Biochemistry, Faculty of Medicine, Chinese University of Hong Kong, Shatin, N.T.
Young
J D
JD
D000241:Adenosine / Q000378:metabolism; D001798:Blood Proteins / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D002463:Cell Membrane Permeability; D004910:Erythrocyte Membrane / Q000378:metabolism; D006801:Humans; D007288:Inosine / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism*; D033703:Nucleoside Transport Proteins; D009705:Nucleosides / Q000378:metabolism*; D014529:Uridine / Q000378:metabolism
D001798:Blood Proteins; D002352:Carrier Proteins; D008565:Membrane Proteins; D033703:Nucleoside Transport Proteins; D009705:Nucleosides; D007288:Inosine; D000241:Adenosine; D014529:Uridine