The Monovalent Cation:Proton Antiporter-1 (CPA1) Family (TC 2.A.36) The CPA1 family is a large family of proteins derived from Gram-positive and Gram-negative bacteria, blue green bacteria, yeast, plants and animals. Transporters from eukaryotes have been functionally characterized, and all of these catalyze Na+:H+ exchange. Their primary physiological functions may be in (1) cytoplasmic pH regulation, extruding the H+ generated during metabolism, and (2) salt tolerance (in plants), due to Na+ uptake into vacuoles. This model is specific for the fungal members of this family. [Transport and binding proteins, Cations and iron carrying compounds]