Overlay of the rkbPAP-sulfate complex (with the bridging oxygen in red), the bridging hydroxide (pink) as observed in pig PAP  and the phosphate as observed in sweet potato PAP . The image demonstrates a plausible trajectory for the substrate with the bridging hydroxide as the nucleophile in catalysis. Inversion of configuration around the phosphorous atom is observed. General legend: Fe(III) is in tan, Zn(II) in grey, carbon in green, oxygen in red, nitrogen in blue, sulphur in orange, hydrogen in white and phosphorous in magenta.
Schenk et al. BMC Structural Biology 2008 8:6 doi:10.1186/1472-6807-8-6