Fig. (1).

Crystal Structure of Bovine XOR. Left; Homodimer structure of bovine XOR. The N-terminal (in red), the C-terminal (in blue) and the intermediate (in yellow) domains contain the iron-sulfur centers, the molybdopterin and the FAD centers. Right: Cofactor arrangements of the enzyme. Figures were generated from PDB ID 1F4Q. Arrows show the directions of electron flow during catalysis. The reduced FAD reacts with either NAD⁺ or oxygen to produce NADH or hydrogen peroxide (H₂O₂) or superoxide (O₂^-). FADH₂ reacts with O₂ to produce H₂O₂ , while FADH produces O₂^- [61, 63]. (The color version of the figure is available in the electronic copy of the article).