Metalloenzymes from a High-Frequency EPR/ENDOR Perspective

The biological functioning of metalloenzymes depends upon a subtle interplay between the redox and substrate-binding properties of the catalytically active metal site. We propose to use novel high-frequency, pulsed EPR techniques to study the reaction mechanism of nitrite reduction in the denitrification cycle and of the oxygenation of flavonols, e.g. quercetin, by copper enzymes. We focus on the electronic structure of the metal site and its ligand sphere and the changes occurring upon substrate binding and electron transfer. This will yield insight into the parameters making biological enzymatic reactions as selective and efficient as they are. As part of the project we will develop 275 GHz ENDOR spectroscopy. Introducing ENDOR at such high frequencies and magnetic fields results in unparalleled resolution, sensitivity, and selectivity.