Cofactor activity of mutants lacking Lys 2092 and/or Phe 2093 as a function of Ptd-L-Ser content in phospholipid vesicles. (A) Activity of fVIII_YFP (■) was compared with fVIII_{YFP 2092} (▲) for vesicles with Ptd-L-Ser content ranging from 0% to 20%. (B) fVIII_{YFP 2093} (▲) was compared with fVIII_YFP (■). (C) fVIII_{YFP 2092/2093} (▲) was compared with fVIII_YFP (■). Results indicate that fVIII_{YFP 2093} has intermediate impairment when Ptd-L-Ser content is less than 12%, whereas fVIII_{YFP 2092} has activity approaching fVIII_YFP. The concentration of factor VIII was 1 U/mL, and vesicle composition was 0% to 20% Ptd-L-Ser, 20% PE, with the balance as PC. Assays were performed as for Figure 2. Each point represents the mean ± SEM for 3 experiments, each performed in duplicate. Data and curve for fVIII_YFP are displayed in panels A to C.