Protease activity in the human erythrocyte: localization to the cell membrane

Proteolytic activity in the mature human erythrocyte was localized to the cell membrane. This activity, which could not be ascribed to contaminating leukocytes in the suspension, was totally absent from the soluble portion of the cell and was more active against hemoglobin subunits than against tetrameric hemoglobin molecules. Pulse-chase experiments confirmed that the membrane proteolytic activity was more active in degrading beta chains that alpha chains. The activity could be extracted from erythrocyte cell membranes, but not from membrane- free hemolysate, by exposure to 0.75-M KSCN. The activity of the protease was dependent on time and temperature and did not require ATP or an energy-generating system for activity.