This subproject is one of many research subprojects utilizing theresources provided by a Center grant funded by NIH/NCRR. The subproject andinvestigator (PI) may have received primary funding from another NIH source,and thus could be represented in other CRISP entries. The institution listed isfor the Center, which is not necessarily the institution for the investigator.The basic reactivity of sulfur-centered radicals is being studied in a variety of different protein environments using Sulfur K-edge X-ray Absorption Spectroscopy as a novel probe of the electronic structure of these biologically-important peptidic radicals. Cysteinyl radicals ([Cys ]) and disulfide anion radicals ([CysS SCys]1-) have been observed or postulated as intermediates in several biological functions including enzymatic catalysis, long-range electron transfer, peptide post-translational modification, cellular redox buffering, and even cellular redox signaling. Electron paramagnetic resonance has been the primary tool used to characterize these radical species but direct observation is compromised by spin-orbit broadening of the signals, which has diminished the effectiveness of the approach. The S 1s->3p pre-edge transition that results from radical character on a sulfur atom is being used to directly probe the electronic structure of these radical species and to investigate the effect of factors such as hydrogen bonding and electron delocalization on the reactivity of these radicals in various protein environments. An important goal of this effort is to develop S K-edge XAS as a powerful and general probe of sulfur radical species to investigate a wide range of biological systems.
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