Involvement of face 1 and face 2 PS residues for APC cofactor activity in plasma clotting assays. The ability of wild-type rPS (▪), F1_FII-Gla_PS-PS (▴), F2_FII-Gla_PS-PS (▾), and F12_PS-Gla_FII-PS (○) to function as APC cofactors was investigated in an FXa 1-stage plasma clotting assay (A) and in an APTT assay (B), as described in Figure 3. F1_FII-Gla_PS-PS and F2_FII-Gla_PS-PS were essentially devoid of cofactor activity, whereas F12_PS-Gla_FII-PS recovered significant APC cofactor activity.