XANES spectroscopy of carp hemoglobin-iron in correlation with the affinity changes of the protein for ligand

How Nanoparticles Modify Adsorbed Proteins: Impact of Silica Nanoparticles on the Hemoglobin Active Site

The adsorption of proteins on surfaces has been studied for a long time, but the relationship between the structural and functional properties of the adsorbed protein and the adsorption mechanism remains unclear. Using hemoglobin adsorbed on silica nanoparticles, we have previously shown that hemoglobin's affinity towards oxygen increases with adsorption. Nevertheless, it was also shown that there were no significant changes in the quaternary and secondary structures. In order to understand the change in activity, we decided in this work to focus on the active sites of hemoglobin, the heme and its iron. After measuring adsorption isotherms of porcine hemoglobin on Ludox silica nanoparticles, we analyzed the structural modifications of adsorbed hemoglobin by X-ray absorption spectroscopy and circular dichroism spectra in the Soret region. It was found that upon adsorption, there were modifications in the heme pocket environment due to changes in the angles of the heme vinyl functions. These alterations can explain the greater affinity observed.

XANES spectroscopy sensitivity to small electronic changes. Case of carp azidomethemoglobin

Spin states equilibrium of hemoglobin-iron varies with external conditions: pH, allosteric effectors, temperature. The small electronic reorganization of the iron caused by the spin state changes has been detected by X-ray absorption near edge structure (XANES) spectroscopy at room temperature. The iron K-edge region which is sensitive to spin state is located in 7110-7130 eV. Here are presented the 100% high spin and 100% low spin XANES spectra of carp azido ferric hemoglobin.