Concentrative Nucleoside Transporters

CNTs are responsible for the intracellular uptake of nucleosides, an energy consuming process which is coupled to the Na+ gradient across the plasma membrane. All three transporters display a relatively high affinity for their substrates but a more selective than ENTs. Pyrimidines are the substrate of choice for CNT1 although it can bind but not transport adenosine. CNT2 prefers purines, although it can transport uridine, and CNT3 is selective for both types of nucleosides. Both CNT1 and CNT2 display a 1:1 stoichiometry (nucleoside:sodium). CNT3 on the other hand transports two Na+ ions per nucleoside, and can also co-transport protons in a pH dependent manner in a 1:1 ratio.
All three CNTs have thirteen transmembrane domains and an extracellular C-terminus responsible for substrate recognition.