Band 3 (BND3)

Anion Exchanger 1  is a phylogenetically preserved transport protein responsible for mediating the electroneutral exchange of chloride (Cl-) for bicarbonate (HCO3-) across a plasma membrane.It is ubiquitous throughout the vertebrates. In humans it is present in two specific sites: the erythrocyte (red blood cell) cell membrane and the basolateral surface of the alpha-intercalated cell (the acid secreting cell type) in the collecting duct of the kidney. The erythrocyte and kidney forms are different isoforms of the same protein.AE1 was discovered following SDS-PAGE gel electrophoresis of erythrocyte cell membrane. The large 'third' band on the electrophoresis gel represented AE1, which was thus initially termed 'Band 3'. The chloride-bicarbonate exchanger in the red cell membrane is not a pump, which would use metabolic energy.