Difference in substrate specificity divides the yeast alkali-metal-cation/H+ antiporters into two subfamilies

Yeast plasma membrane Na+/H+ antiporters (TC 2.A.36) share a high degree of similarity at the protein level. Expression of four antiporters (Saccharomyces cerevisiae Nha1p, Candida albicans Cnh1p, Zygosaccharomyces rouxii ZrSod2-22p and Schizosaccharomyces pombe sod2p) in a Sacch. cerevisiae mutant strain lacking both Na+-ATPase and Na+/H+ antiporter genes made it possible to study the transport properties and contribution to cell salt tolerance of all antiporters under the same conditions. The ZrSod2-22p of the osmotolerant yeast Z. rouxii has the highest transport capacity for lithium and sodium but, like the Schiz. pombe sod2p, it does not recognize K+ and Rb+ as substrates. The Sacch. cerevisiae Nha1p and C. albicans Cnh1p have a broad substrate specificity for at least four alkali metal cations (Na+, Li+, K+, Rb+), but their contribution to overall cell tolerance to high external concentration of toxic Na+ and Li+ cations seems to be lower compared to the antiporters of Schiz. pombe and especially Z. rouxii.