First principle calculations for the non-heme iron centers of lipoxygenases:: Geometrical and spectral properties

Lipoxygenases (LOs), which are non-heme-iron-containing enzymes, play a vital role in plant and mammalian organisms. Their active sites have been probed by various spectroscopic techniques both in resting (Fe2+) and active (Fe3+) forms. Several crystal structures have been reported for ferrous forms of LOS; nevertheless, many unresolved questions have still remained. In particular, subtle differences in the first coordination sphere of the iron center seem to be very important for their catalytic activity thus any information about details of these structures is of great value. In this report, we present results of first principle calculations for reliable models of ferrous and ferric active sites of LOs undertaken to resolve ambiguities in structure of both resting and active forms of the iron sites in lipoxygenases. Geometrical parameters of optimized models are compared with crystallographic and EXAFS data. Time-dependent density functional theory (TDDFT) results for spectroscopic states are confronted with the relevant experimental results to validate the models and to gain an insight into the electronic structure of ferric and ferrous active sites. Overall good agreement between the calculated and experimental positions of the absorption bands is found, and where possible, the sources of discrepancies are discussed.