The selective 15N isotope labeling was used for the identification of the nitrogen involved in a hydrogen bond formation with the semiquinone in the high-affinity QH site in the cytochrome bo3 ubiquinol oxidase. This nitrogen produces dominating contribution to X-Band 14N ESEEM spectra. The 2D ESEEM (HYSCORE) experiments with the QH site SQ in the series of selectively 15N labeled bo3 oxidase proteins have directly identified the Nε of R71 as an H-bond donor. In addition, selective 15N labeling has allowed us for the first time to determine weak hyperfine couplings with the side-chain nitrogens from all residues around the SQ. Those are reflecting a distribution of the unpaired spin density over the protein in the SQ state of the quinone processing site.
ASJC Scopus subject areas
- Colloid and Surface Chemistry