Gn. George et al., THE MOLYBDENUM SITE OF SULFITE OXIDASE - A COMPARISON OF WILD-TYPE AND THE CYSTEINE-207 TO SERINE MUTANT USING X-RAY-ABSORPTION SPECTROSCOPY, Journal of the American Chemical Society, 118(36), 1996, pp. 8588-8592
X-ray absorption spectroscopy at the molybdenum and sulfur K-edges has
been used to probe the active site of wild-type and cysteine 207 -->
serine mutant human sulfite oxidases. We compare the active site struc
tures in the Mo(VI) oxidation states: the wild-type enzyme possesses t
wo Mo=O ligands at 1.71 Angstrom and three Mo-S ligands at 2.41 Angstr
om. The mutant molybdenum site is a novel trioxo site with Mo=O bond l
engths of 1.74 Angstrom, with two Mo-S ligands at 2.47 Angstrom. We co
nclude that cysteine 207 is a ligand of molybdenum in wild-type human
sulfite oxidase, and that, in the mutant, the Mo is ligated to an extr
a oxo group rather than the hydroxyl of the substituent serine 207.