Session: Inorganic Spectroscopy:

Dioxygenases are microbial non-heme iron enzymes playing a key role in reactions that are important for the cellular metabolism and the global carbon cycle. Cysteine dioxygenase (CDO) is a member of the thiol dioxygenase family and the first enzyme in the detoxification of cysteine in humans. The active site of CDO contains an iron ion coordinated by a three histidine residues, to which cysteine and oxygen coordinate during the catalytic cycle. However, the mechanism by which dioxygen is activated and the reactive intermediates of the incorporation of the two oxygen atoms in the final product remain to be elucidated.
The aim of this study is to use Mössbauer spectroscopy to gain insight in the electronic structures of the intermediates formed in the reaction of a complex mimicking the CDO active site with O₂. The complexes studied feature N4 coordination with pyridyl/imidazolyl N-donors in place of the 3His triad a thiol coordinated adjacently, leaving an open position for O₂. In this poster, we present the initial Mössbauer characterization of the ferrous Fe^II complexes modeling the resting state of the enzyme, as well as the spectra of the intermediates obtained by reacting the Fe(II) complexes with dioxygen in tetrahydrofuran solution at low temperatures. The starting complexes have isomer shifts around 1 mm/s and large quadrupole splittings, typical for pentacoordinated Fe(II) ions with N/O coordination. Following the color change a first intermediate incorporating oxygen is accumulated, which presents an isomer shift of ~ 0.5 mm/s, and it has a diamagnetic electronic ground state. The poster will present the variable field-variable temperature spectra of these molecules and propose structures based on the Mössbauer data and other spectroscopic methods.

Adam Fiedler

Marquette University

Appearances