3D-model of Kluyveromyces lactis thioredoxin reductase performed with PyMOL Molecular Viewer http://pymol.sourceforge.net/ (A) Domains are marked in colours. Green: FAD binding domain (residues 32-156 and 281-349). Blue: NADPH binding domain. The two Cys that make up the active site are marked in red. (B) Residues different from S. cerevisiae cytosolic thioredoxin reductase are marked in blue, these differences do not affect significantly the overall structure of the protein.