English: The AOX octamer with domain colors shown. Colors are as in Fig 5a: FAD-binding domain (red); FAD covering lid (pink); extended FAD-binding domain (yellow); flavin attachment loop (green) and intermediate region (light green); substrate-binding domain (cyan). Helix H12, which forms crystal contacts, is shown in orange. The longest AOX-specific insert 481–548 is shown in dark blue, other AOX-specific sequences are colored purple. The tetramer interface is exclusively made by AOX-specific elements (dark blue and purple).