Proteolytic cleavage of band 3 protein in relation to anion transport in fish (Oncorhynchus mykiss) red blood cells

1. The effects of trypsin and chymotrypsin on HCO3−/Cl− exchange through red blood cell membranes of humans and trout were studied. 2. To measure the anion exchange we used a right-angle light-scattering technique by applying the Jacobs-Stewart cycle in ammonium solution and the osmotiration method at constant cell volume. 3. The Cl− flux in human red blood cells remained unaltered after treatment with external trypsin and chymotrypsin while in trout red blood cells the flux decreased. 4. This partial inhibition of anion transport in fish, ranging from 30 to 40%,suggest that one or several of the cleavage sites in band 3 protein, essential for anion transport function, are exposed in fish red blood cells. 5. In human red blood cells the fragments of band 3 which are affected by proteolytic digestion, retain their tertiary structure because there is no influence on anion transport