“…2,3 Before the human genome project, our understanding of cells and how they take up nucleosides was based on kinetic experiments in the 1980's. 4 The literature still sometimes reflects the nomenclature adopted for the nucleoside transporters at that time. Long before we knew the gene sequences, scientists showed two classes of membrane proteins, one which acted in an equilibrative manner and another which transported purine and pyrimidine nucleosides against the concentration gradient.…”