Calcium protects _EC domain from digestion by plasmin. Recombinant _EC was digested with plasmin (0.5 U/mL) for the times indicated in the presence of either EDTA (5 mmol/L) or CaCl₂ (5 mmol/L) as described in Materials and Methods. Samples were run on 4% to 20% gradient SDS-PAGE under reducing conditions.