Human factor VIII procoagulant activity and phospholipid interaction

The interaction between purified human factor VIII and phospholipid vesicles was investigated. The binding of factor VIII to an equimolecular mixture of phosphatidylserine (PS) and phosphatidylcholine (PC) was studied by sucrose gradient ultracentrifugation (10–40% w/v saccharose in 0.01 M Tris-HCl/0.15 M NaCl buffer (pH 7). In the absence of phospholipids all factor VIII activities (VIII : C, VIII R : WF and VIII R : AG) were found in the zone of highest sucrose density including the factor VIII related protein subunit (200 000 molecular weight). In the presence of an equimolecular mixture of PS/PC VIII R : WF activity, VIII R : AG and a factor VIII related protein still migrated to the bottom of the tube, while VIII : C activity remained at the top where phospholipids were found. Thus a dissociation phenomenon between VIII : C and the other factor VIII relateda activities was apparent in the presence of phospholipids. These results also demonstrate the binding of factor VIII : C to certain active phospholipids.