InterPro domain: IPR034764

Nucleosides are hydrophilic molecules and require specialised transport proteins for permeation of cell membranes. There are two types of nucleoside transport processes: equilibrative bidirectional processes driven by chemical gradients and inwardly directed concentrative processes driven by an electrochemical gradient [ 1 ]. The two types of nucleoside transporters are classified into two families: the solute carrier (SLC) 29 and SLC28 families, corresponding to equilibrative and concentrative nucleoside transporters, respectively [ 2 ].

Equilibrative nucleoside transporters (ENTs) are integral membrane proteins which enable the movement of hydrophilic nucleosides and nucleoside analogues down their concentration gradients across cell membranes. ENT family members have been identified in humans, mice, fish, tunicates, slime molds, and bacteria [ 3 ].

This entry represents equilibrative nucleoside transporters (ENT) 1 and 2. Both ENT 1 and 2 import and export nucleosides across the membrane (equilibrative transportation). ENT1 (also known as Slc29a1) is inhibited by low concentrations of nitrobenzylmercaptopurine riboside (NBMPR), whereas ENT2 (also known as Slc29a2) is much less sensitive [ 4 ].

1. Recent advances in the molecular biology of nucleoside transporters of mammalian cells. Biochem. Cell Biol. 76, 761-70
2. The human concentrative and equilibrative nucleoside transporter families, SLC28 and SLC29. Mol. Aspects Med. 34, 529-47
3. Molecular evolution of the equilibrative nucleoside transporter family: identification of novel family members in prokaryotes and eukaryotes. Mol. Biol. Evol. 19, 2199-210
4. Molecular cloning and characterization of a nitrobenzylthioinosine-insensitive (ei) equilibrative nucleoside transporter from human placenta. Biochem. J. 328 ( Pt 3), 739-43