APC anticoagulant cofactor activity of recombinant mouse PS. (A) Modified APTT assay. Increasing concentrations of recombinant mouse wild-type (WT) PS (●) or PS-K196E (▪) were added to normal mouse pooled plasma, and a modified APTT clotting assay was performed in the presence of recombinant mouse APC. (B) FXa 1-stage clotting assay. Increasing concentrations of recombinant mouse WT PS (●) or PS-K196E (▪) were added to normal mouse pooled plasma, and an FXa 1-stage clotting assay was performed in the presence of recombinant mouse APC. Each assay was performed in triplicate, and data are shown as mean ± SD.