Human MATE1 (Multidrug And Toxic Compounds Extrusion 1, hMATE1) is an electroneutral H⁺/organic cation (OC) exchanger responsible for the final excretion step of structurally unrelated toxic organic cations in kidney and liver. To elucidate the molecular basis of the substrate recognition by hMATE1, we substituted the glutamate residues Glu273, Glu278, Glu300 and Glu389, which are conserved in the transmembrane regions, for alanine or aspartate and examined the transport activities of the resulting mutant proteins using tetraethylammonium (TEA) and cimetidine as substrates after expression in HEK293 cells. All of these mutants except Glu273Ala were fully expressed and present in the plasma membrane of the HEK293 cells. TEA transport activity in the mutant Glu278Ala was completely absent. Both Glu300Ala and Glu389Ala and all aspartate mutants exhibited significantly decreased activity. Glu273Asp showed higher affinity for cimetidine while it has reduced affinity to TEA. Glu278Asp showed decreased affinity to cimetidine. Both Glu300Asp and Glu389Asp had lowered affinity to TEA, while the affinity of Glu389Asp to cimetidine was four-fold higher than that of the wild type transporter with about a four-fold decrease in V_max value. Both Glu273Asp and Glu300Asp had altered pH dependence for TEA uptake. These results suggest that all of these glutamate residues are involved in binding and/or transport of TEA and cimetidine, but that their individual roles are different to each other.