Inactivation of FVIIIa by different concentrations of APC, effects of FV:R506 and FV:Q506. The APC-cofactor effects of protein S and wtFV or FV:Q506, were determined at different concentrations of APC (0, 0.020, 0.078, 0.3, 0.125, and 5 nmol/L) in the FVIIIa degradation assay. A, (▵), wtFV (11 nmol/L) and protein S (100 nmol/L); (▴), wtFV (11 nmol/L) and protein S (4.4 nmol/L); (□), 100 nmol/L protein S without FV; (▪) 4.4 nmol/L protein S without FV. B, (○), FV:Q506 (11 nmol/L) and protein S (100 nmol/L); (•), FV:Q506 (11 nmol/L) and protein S (4.4 nmol/L); (□), 100 nmol/L protein S without FV:Q506; (▪), 4.4 nmol/L protein S without FV:Q506. The results were expressed as percentage of respective control with APC. Each data point represents one of two experiments with similar results.