Hyperfine structure resolved by 2 to 4 GHz EPR of cytochrome c oxidase

Using low frequency 2 to 4 GHz EPR at 10 K, we have resolved previously unseen hyperfine structure associated with the EPR-detectable copper signal of cytochrome c oxidase. The observed hyperfine structure appears consistent with hyperfine coupling to copper; although to account for all of the observed structure, an additional magnetic interaction is required as well. This work points out the utility of the 2 to 4 GHz EPR technique for resolving electronic hyperfine structural information from copper and possibly other paramagnetic sites in biomolecules when random variation in electronic g values is a cause of EPR line-broadening.