This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. We propose to use sulfur x-ray absorption edges to track physiologically significant oxidation of sulfur in two systems 1) the oxidation of methionine residues in the small heat shock protein from chloroplasts and 2) the persulfide intermediate generated during Fe-S cluster assembly in the enzyme cysteine desulfurase. For the first system, we have initial XAS measurements indicating that methionine oxidation occurs in vivo in response to heat stress and overproduction of the chloroplast small heatshock protein (cHsp). We would like to improve these measurements with better signal to noise and to extend these studies to include the process of recovery from oxidative stress. For the second system, we have already verified the validity of using rapid acid quenched samples for sulfur XAS. We will now focus on making measurements of the frozen persulfide intermediate. The long term goal of the second project is to kinetically monitor the insertion of sulfur into the product Fe-S cluster using sulfur XANES.
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