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Electron paramagnetic resonance (EPR) spectroscopy is a technique that provides detailed molecular level information on paramagnetic centres. In our research we utilize EPR spectroscopy to investigate the role and structure of bioorganic radicals that play key role in some of the fundamental biological processes.

Bioorganic radicals, such as metallocofactors and amino acid-based radicals, are essential in life because they are involved in photosynthesis, respiration, synthesis of DNA building blocks, biological nitrogen fixation and many more. They serve as redox-active intermediates in electron transfer reactions or reactive cofactors at the active site of enzymes. Therefore, the study of bioorganic radicals is crucial to understand enzymatic reaction mechanisms and to design analogous synthetic systems.

Proton-coupled electron transfer in proteins

Enzyme-mediated proton-coupled electron transfer (PCET) processes are fundamental and ubiquitous in biology. They are central to our understanding of reactions in primary metabolism including photosynthesis, respiration and synthesis of DNA building blocks. These reactions share a common catalytic feature, a tyrosyl or modified tyrosyl radical (Y•) that is involved in either concerted or stepwise PCET steps. E. coli class Ia ribonucleotide reductase (RNR) serves as a paradigm for diverse PCET mechanisms in enzymes. It catalyzes the reduction of ribonucleotides to deoxyribonucleotides via an unprecedented radical transfer process over 35 Å using at least four Y•s (Y122 and [W48] and Y356 in β2 to Y731 and Y730 and C439 in α2).

We used multi-frequency (9, 34, 94 and 263 GHz) EPR, ENDOR, PELDOR and rapid-freeze-quench (RFQ)-EPR spectroscopies in combination with incorporation of unnatural amino acids to investigate the PCET mechanism at the subunit interface of this protein during catalysis.





A recent example of our research on metalloproteins is the recently discovered small lipoxygenase (LOX) from cyanobacteria. Lipoxygenases are metal-containing (Fe or Mn) enzymes that catalyse the regio- and stereospecific insertion of dioxygen into polyunsaturated fatty acids. We have characterized the metal site of LOX from cyanobacteria as Fe via Fe/Mn substitution and EPR spectroscopy.