Inactivation of FV(a) by APC. Reaction mixtures containing 50 μM PCPS and 500 nM pt-rFV (●), pt-rFVa (□), hFV-810 (⧫), or rFVa (△) were incubated with either 10 nM or 750 nM (inset) APC. At selected time intervals, samples were removed for cofactor activity (A) or SDS-PAGE under nonreducing (B) or reducing conditions (C). Protein bands subjected to N-terminal sequence analysis are marked and annotated according to the scheme below the gels: A2_C-B-A3-C1-C2, 508-1430; A1-A2_N, 1-507; B-A3-C1-C2, 743-1430; A2_C, 508-742. We speculate that *B-A3-C1-C2 and *A2_C are cleaved at their C-terminal ends because their N-terminal sequence was determined to be the same as B-A3-C1-C2 and A2_C, respectively. APC can be visualized and is denoted by a brace. The functional measurements and gels are representative of 2 similar experiments.