<P> Band 3 is present in the basolateral face of the α - intercalated cells of the collecting ducts of the nephron, which 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: </P> <Ul> <Li> Electroneutral chloride and bicarbonate exchange across the plasma membrane on a one - for - one basis . This is crucial for CO uptake by the red blood cell and conversion (by hydration catalysed by carbonic anhydrase) into a proton and a bicarbonate ion . The bicarbonate is then excreted (in exchange for a chloride) from the cell by band 3 . </Li> <Li> Physical linkage of the plasma membrane to the underlying membrane skeleton (via binding with ankyrin and protein 4.2). This appears to be to prevent membrane surface loss, rather than having to do with membrane skeleton assembly . </Li> </Ul> <Li> Electroneutral chloride and bicarbonate exchange across the plasma membrane on a one - for - one basis . This is crucial for CO uptake by the red blood cell and conversion (by hydration catalysed by carbonic anhydrase) into a proton and a bicarbonate ion . The bicarbonate is then excreted (in exchange for a chloride) from the cell by band 3 . </Li> <Li> Physical linkage of the plasma membrane to the underlying membrane skeleton (via binding with ankyrin and protein 4.2). This appears to be to prevent membrane surface loss, rather than having to do with membrane skeleton assembly . </Li>

What does band 3 protein do on red blood cells
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