Band 3
Band 3 anion transport protein also known as anion exchanger 1 (AE1) or band 3 or solute carrier family 4 member 1 (SLC4A1) is a protein that in humans is encoded by the SLC4A1 gene.
Band 3 anion transport protein is a phylogenetically preserved transport protein responsible for mediating the exchange of chloride (Cl−) for bicarbonate (HCO3−) across a plasma membrane. Functionally similar members of the AE clade are AE2 and AE3.
Function
This is present in the α-intercalated cells of the collecting ducts of the nephron. these are the main acid secreting cells of the kidney. They generate hydrogen ions and bicarbonate ions from carbon dioxide and water - a reaction catalysed by Carbonic anhydrase. The hydrogen ions are pumped into the collecting duct tubule by vacuolar H+ ATPase, the apical proton pump, which thus excretes acid into the urine. kAE1 exchanges bicarbonate for chloride on the basolateral surface, essentially returning bicarbonate to the blood. Here it performs two functions: