Degradation of Band‐3 Glycoprotein in vitro by a Protease Isolated from Human Erythrocyte Membranes

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Abstract
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 adsorbent is active on band-3 glycoprotein in a non-ionic detergent solulion 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 omittcd from the membrane extract, an inactive form of this enzyme can be purified. By DEAE-cellulose chromatography this inactive form can be convcrted into the active form, presumably by dissociation of an enzymeinhibitor complex.