APC cleavage of recombinant wild-type and mutant murine FV. Western blot analysis was performed using a rabbit anti-murine FV antibody which recognizes an epitope(s) on the N-terminal half of the FV heavy chain (residues 1-305). Lanes A through E are untreated conditioned media, lanes F through J are following activation with thrombin, and lanes K through O are following thrombin activation and subsequent treatment with APC. Lanes A, F, and O are conditioned media from mock-transfected cells; lanes B, G, and K, from cells transfected with wild-type FV; lanes C, H, and L, from cells transfected with R305Q mutant FV; lanes D, I, and M, from cells transfected with R504Q mutant FV; lanes E, J, and N, from cells transfected with R305Q/R504Q mutant FV.