Mononuclear non-heme iron centers are present in a wide range of enzymes that carry out interesting biological processes involving O₂. My research focuses on a sub-class of the mononuclear non-heme iron family called the intra- and extradiol dioxygenases. These enzymes have similar ligands around the iron centers, namely histidine, tyrosinate and water for intradiol dioxygenases, and histidine, glutamate and water for extradiol dioxygenases. Both of them are involved in the biodegradation of lignin and other catecholic rings; however, there is a huge difference in the position of ring cleavage (Figure 1) and reaction mechanism. Intradiol dioxygenases employ a Fe³⁺ center and substrate binding to the ferric site activates substrate for direct attack by O₂. In contrast, extradiol dioxygenases use a Fe²⁺ center and substrate binding to the ferrous site activates this site for O₂ binding and reaction.

The main goal of my project is to identify the factors governing the different chemical behaviors towards O₂ for these two similar classes of enzymes. We have applied various spectroscopic techniques along with DFT calculations to understand the active site geometric and electronic structure. The experimentally-calibrated DFT protocol is then applied to study the O₂ reaction coordinates of these two different catechol dioxygenases.