A, MF-AnxA1 (input) was incubated with resting PMN-derived membrane (MEM) fractions in the absence or presence of phenylmethylsulfonylfluoride (PMSF, 1 mm) or heat-inactivated samples (boil). B, MF-AnxA1 (input) was incubated with 50 milliunits of HNE (left panel) or 10 milliunits of PR3 (right panel), treated with/without 1 mm PMSF or 0.1–1 mm eglin C. C, as in panel A, PMN-derived membrane (MEM) fractions were incubated with 1 mm PMSF or 0.1–1 mm eglin C. In all cases, intact MF-AnxA1 was recovered and immunoblotted with anti-c-Myc antibody (upper panels) and resultant N-terminal-cleaved proteolytic fragments obtained by IP and immunoblotting with anti-FLAG antibody (lower panels). Blots are representative from at least three distinct experiments.