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. Seems to play an important role in colonic sodium absorption. Interacts with CHP1 and CHP2. Predominantly in small intestine, colon, and stomach, with much lower levels in skeletal muscle, kidney, brain, testis, uterus, heart and lung. Phosphorylated (Possible). Belongs to the monovalent cation:proton antiporter 1 (CPA1) transporter (TC 2.A.36) family. The number, localization and denomination of hydrophobic domains in the Na(+)/H(+) exchangers vary among authors. PubMed:8595899 sequence was originally thought to originate from human.