Involved in pH regulation to eliminate acids generated by active metabolism or to counter adverse environmental conditions. Major proton extruding system driven by the inward sodium ion chemical gradient. Plays an important role in signal transduction. Oligomer (By similarity). Interacts with CALM1 in a calcium-dependent manner (By similarity). Interacts with TESC (By similarity). Interacts (via the juxtamembrane region of the cytoplasmic C-terminal domain) with CHP1; the interaction occurs at the plasma membrane in a calcium-dependent manner (By similarity). Interacts with CHP2; the interaction occurs in a calcium-dependent manner (By similarity). Colocalizes with CHP1 and CHP2 at the reticulum endoplasmic and plasma membrane. O-glycosylated. Ubiquitinated, leading to its degradation by the proteasome. Ubiquitination is reduced by CHP1 (By similarity). Belongs to the monovalent cation:proton antiporter 1 (CPA1) transporter (TC 2.A.36) family. The region between transmembrane regions M4 and M5 and between M6 and M7 (also termed intracellular loops IL2 and IL4, respectively) seem to be localized at least in part in the membrane. The hydrophobic region H10 is proposed to be located within the membrane. The interacting region with TESC is conflicting: In human, it has been reported that SLC9A1 interacts with TESC via the juxtamembrane region of the cytoplasmic C-terminal domain, including residues 507-549. However, another publication has reported interaction with TESC via residues 637-820, the region of the cytoplasmic C-terminus more distal to the membrane.