Figure 1.

One subunit of the bovine xanthine oxidoreductase homodimer (PDB ID: 1JRO).⁴⁷ The close-up represents the XOR’s active regions in the redox reaction that are almost linearly positioned in the order of MoCo, $\text{F}{\text{e}}_{\text{2}}–{\text{S}}_{\text{2}}$, and FAD. Hydrogen atoms are not presented for more clarity, and four cysteine residues bound to the $\text{F}{\text{e}}_{\text{2}}–{\text{S}}_{\text{2}}$ cluster’s irons are shown in the sticks.