Degradation of band-3 glycoprotein in vitro by a protease isolated from human erythrocyte membrane.

The use of soybean-trypsin-inhibitor-Sepharose-4B to purify a protease present in human erythrocyte membranes is described. The fraction bound in the presence of calcium to the affinity absorbent is active on band-3 glycoprotein in a non-ionic detergent solution at neutral pH. Band-3 glycoprotein is degraded into components having the mobilities of the proteins of bands 4.5, 7 and of lower molecular weights. When calcium is omitted from the membrane extract, an inactive form of this enzyme can be purified. By DEAE-cellulose chromatography this inactive form can be converted into the active form, presumably by dissociation of an enzyme-inhibitor complex.