Electron Paramagnetic Resonance Spectroscopy of Metalloproteins

: Electron paramagnetic resonance (EPR) is a spectroscopic technique that is sensitive to the presence of unpaired electrons and, therefore, is a powerful tool for the study of proteins containing complex metallocofactors. When a magnetic field is applied to a transition metal-containing system with unpaired electrons and the sample is irradiated with microwaves, a spin transition can be observed. Through detailed analysis of the resulting EPR spectrum, one can extract parameters that can provide information about the electronic environment of the unpaired electrons found on the metal centers. Here, a basic introduction to the theory of EPR and the instrumentation is presented along with procedures for obtaining EPR spectra of sensitive metalloprotein species.