Figure 3.

FAD- and Fe/S II-binding sites of XDH. The view is into the cleft toward the si-site of the flavin ring. Several amino acids are drawn in ball-and-stick mode: Thr 262, Glu 45, and Gly 48, whose main chain carbonyl atoms are close to the 7α- and 8α-methyl groups of the flavin ring; Phe 337 in stacking interaction with the re-side of the pyrimidine part of the flavin ring; Asp 429, whose side chain lies in plane with the flavin and only 3.6 Å from its C6 atom; Arg 426, whose side chain becomes the one closest to the flavin ring in XO.