SDS-PAGE and Western blotting of the A1/A3-C1-C2 dimeric subunit and isolated A1 subunit cleavage reactions. (A) A1/A3-C1-C2 subunit (250 nM) was incubated with APC derivatives (40 nM) on 100 μM PC/PS vesicles in 5 mM Ca²⁺ for 5 minutes at 37°C. Following electrophoresis, proteins were transferred to nitrocellulose membranes and Western blotted by the 58.12 anti-A1 subunit monoclonal antibody. (B) Procedures were the same as those described in panel A except that the Western blot is derived from the incubation of A1 subunit (2500 nM) with APC derivatives (250 nM) on 100 μM PC/PS vesicles in 5 mM Ca²⁺ for 4 hours at 37°C.