Homology model of the triplicated A domains of human FVIII. (Left) FVIII α-carbon ribbon viewed from 'top' of the molecule down the pseudo threefold axis. A1 (red), A2 (blue), and A3 (green); this color coding is consistent throughout this and subsequent figures. Cysteine residues predicted to participate in disulphide links are highlighted in yellow. (Right) View perpendicular to the axis, with A1 to the front and the 'top' of the molecule bearing the loops anchoring the first and second β-strands of subdomains corresponding to the d subdomains of hCp; the A3 C terminus is marked to the left. Also marked are the location of insertion points of acidic peptides in FVIII; peptide a1 may be inserted on the surface between A1 and A2, whereas peptide a2, B domain and third acidic peptide a3 may be inserted on surface between A2 and A3.