XAS characterization of the active sites of novel intradiol ring-cleaving dioxygenases: hydroxyquinol and chlorocatechol dioxygenases.

The intradiol cleaving dioxygenases hydroxyquinol 1,2-dioxygenase (HQI,20) from Nocardiodes simplex 3E, chlorocatechol 1,2-dioxygenase (CIC1,20) from Rhodococcus erythropolis ICP, and their anaerobic substrate adducts (hydroxyquinol-HQ1,20 and 4-chlorocatechol-CIC1,20) have been characterized through X-ray absorption spectroscopy. In both enzymes the iron(III) is pentacoordinated and the distance distribution inside the Fe(III) first coordination shell is close to that already found in the extensively characterized protocatechuate 3,4-dioxygenase. The coordination number and the bond lengths are not significantly affected by the substrate binding. Therefore it is confirmed that the displacement of a protein donor upon substrate binding has to be considered a general step valid for all intradiol dioxygenases.