SLC28 family membersappear to have 13 TM segments with cytoplasmic N-termini and extracellular C-termini, and function as concentrative nucleoside transporters.

A further two Na⁺-dependent (stoichiometry 1 Na⁺ : 1 nucleoside (in)) nucleoside transporters have been defined on the basis of substrate and inhibitor selectivity: CNT4 (N4/cit, which transports uridine, thymidine and guanosine) and CNT5 (N5/csg, which transports guanosine and adenosine, and may be inhibited by nitrobenzylmercaptopurine ribonucleoside).

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3. Gupte A, Buolamwini JK. (2009) Synthesis and biological evaluation of phloridzin analogs as human concentrative nucleoside transporter 3 (hCNT3) inhibitors. Bioorg. Med. Chem. Lett., 19 (3): 917-21. [PMID:19097778]

4. Larráyoz IM, Fernández-Nistal A, Garcés A, Gorraitz E, Lostao MP. (2006) Characterization of the rat Na+/nucleoside cotransporter 2 and transport of nucleoside-derived drugs using electrophysiological methods. Am. J. Physiol., Cell Physiol., 291 (6): C1395-404. [PMID:16837649]

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