Model of Xase complex reveals multiple intermolecular contacts between fVIIIa and fIXa. (A) Contacts between fVIIIa A2 domain (dark blue) and fIXa exosite II (light green). (B) Docking between fVIIIa A3 domain (cyan) and fIXa 99-loop (light green). (C) Contacts between fVIIIa C2 domain (cyan) and fIXa Gla domain (dark green). (D-E) Electrostatic surface potential (D) and cartoon representation (E) of fVIIIa (dark gray) and fIXa (light gray). Inset depicts contacts between fVIIIa acidic residues and fIXa residue K80.