The SLC9 gene family encode proteins (sodium/proton exchangers, NHE or NHX) which exchange sodium (influx) for protons (efflux) electroneutrally. This mechanism is important because many metabolic processes generate acids which need to be removed to maintain pH. This is the major proton extruding system in cells, driven by the inward sodium ion chemical gradient. To date, there are eleven NHE genes, NHE1-11. NHE1-5 exchange cations at the cell membrane. NHE6-9 exchange cations at endosomal membranes or the trans-golgi network membranes.