Molybdenum EXAFS of the Desulfovibrio gigas Mo(2Fe-2S) protein--structural similarity to "desulfo" xanthine dehydrogenase.

The molybdenum EXAFS of the Mo(2Fe-2S) protein from Desulfovibrio gigas has been examined using fluorescence detection and synchrotron radiation. In the oxidized form the molybdenum environment is found to contain two terminal oxo groups and two long (2.47 A) Mo-S bonds. Evidence was also found for an oxygen or nitrogen donor ligand at 1.90 A. Addition of dithionite to the oxidized enzyme results in loss of a terminal oxo group, perhaps due to protonation. In addition, a 0.1 A contraction in the Mo-S bond lengths is observed. The behavior of both oxidized and dithionite-treated forms is similar to that observed previously with "desulfo" xanthine oxidase.