Western blotting to visualize APC-mediated cleavage of FV in the FVIIIa degradation assay. To investigate whether wtFV and mutant FV were cleaved by APC in the FVIIIa degradation assay, aliquots were drawn from the assay and analyzed by Western blotting using an antibody reacting with the amino acid sequence carboxy-terminal of the Arg-306 cleavage site. The FVIIIa degradation was performed as in Fig 2 using 11 nmol/L FV. Aliquots for analysis were drawn before and after (a) the 2.5 minutes incubation in the factor FVIIIa degradation assay.