A. Giovannelli

XANES study of iron displacement in the haem of myoglobin

The XANES (X‐ray absorption near edge structure) spectra of deoxy human adult haemoglobin (HbA) and myoglobin (Mb) have been measured at the wiggler beam line of the Frascati synchrotron radiation facility. The XANES are interpreted by the multiple scattering cluster theory. The variations in the XANES between HbA and Mb are assigned to changes in the Fe‐porphyrin geometry.

Increase of the Fe effective charge in hemoproteins during oxygenation process

The x-ray absorption near edge structure (XANES) spectra of hemoglobin and myoglobin have been measured at the wiggler beam line of the Frascati Synchrotron Radiation Facility. The energy shifts of the iron absorption jump edge and the chemical shifts of the bound excited state at threshold of 1s core excitations, going from deoxygenated to oxygenated form, are interpreted as evidence of some increase of the positive effective charge on the iron atom upon oxygenation.

Xanes (X-ray absorption near edge structure) of V in vanadium-iron phosphate glasses

The X-ray Absorption Near-Edge Structure (XANES) of V in vanadium-iron glasses (50P2O5 + (50−x)FeO + xV2O5) have been measured. The effective charge of V ions in glasses has been determined. At low V2O5 concentration (x ∼ 5) only V4+ with 6-fold coordination is present on the contrary a static mixed valence state (V4+, V5+) has been found at high concentrations 20⩽x⩽50. The results explain the electron hopping conductivity effects at high V2O5 concentration (x ∼ 50) involving V4+ − V5+ pairs and at low V2O5 concentration (x≅10) involving V4+ − Fe3+ pairs.

X-ray absorption near edge structure (XANES) determination of calcium sites of troponin C and parvalbumin

Using synchrotron radiation at the Frascati storage ring ADONE, the X-ray Absorption Near Edge Structure (XANES) has been applied to determine homologies and modifications of the local structure of the calcium binding sites of troponin C. In all four calcium binding sites, Ca2+ appears to be co-ordinated to carboxyl and carbonyl groups in a characteristic configuration. No structural difference has been found between high and low-affinity sites. A distortion of the Ca2+ site geometry by binding of Mg2+ has been observed. The XANES of parvalbumin has been measured and found to be different from troponin C. A tentative identification of the characteristic XANES spectra of the two different Ca2+ sites in this protein is reported.

Determination of CO and CN bond angles by X-ray absorption near edge structure in chelated protoheme in solution

Abstract X-ray absorption near edge structure (XANES) spectra of a model compound chelated protoheme methyl ester in solution reveal a linear Fe-C-N configuration and a bent Fe-C-O configuration, although there are no distal steric effects.

Aluminum site structure in serum transferrin and lactoferrin revealed by synchrotron radiation X-ray spectroscopy

The Al site structure of serum transferrin and lactoferrin is investigated using X-ray absorption near edge structure (XANES) spectroscopy. Al K-edge spectra in the mono- and dialuminum forms of the proteins have been recorded for the first time. Our results show that the aluminium ion is hexa-coordinated in an octahedral-like symmetry and that the monoaluminum form, where only the C-terminal binding site is saturated, has an increased structural distortion around the metal site.

Apparatus for time‐resolved x‐ray absorption spectroscopy using flash photolysis

A system for time‐resolved data acquisition is described. It is based on a Nd‐YAG power laser, five NaI scintillators coupled with five photomultiplier tubes, a fast multichannel analyzer, a cryostat, and a Macintosh II computer (system controller and data acquisition). By means of this apparatus, time‐resolved x‐ray spectra of CO‐myoglobin will be acquired using the synchrotron radiation emitted by a wiggler magnet.

Oxygen bonding in human hemoglobin and its isolated subunits: a XANES study.

The X-ray absorption near edge structure (XANES) spectra of the human adult and foetal hemoglobin, of the isolated alpha and beta chains, in the oxygenated forms, and of the oxymyoglobin and carp oxyhemoglobin have been measured at the wiggler beam line of the Frascati Synchrotron radiation facility. The bonding angle of oxygen molecule at the iron site in these hemoproteins in solution, has been measured using the multiple scattering theory for data analysis.

Constraints of T conformation of carp azide hemoglobin on Fe site structure

The iron site structure modifications induced by the transition from the quaternary R to T structure in ferric carp azide hemoglobin have been detected from analysis of multiple scattering resonances in the XANES (X‐ray absorption near edge structure) spectra. High signal‐to‐noise XANES spectra measured at the Frascati ‘wiggler’ synchrotron radiation facility reveal that the forces on the Fe active site, due to the transition from the R to T quaternary conformation, only induce the tilting of the porphyrin plane and probably also of the proximal histidine. The variation of the Fe‐N mean distance is not detected by XANES spectroscopy and therefore it is less than 0.01 Å.

Heterogeneity of the isolated subunits of the fetal and adult human hemoglobin in solution, detected by XANES spectroscopy

Differences in the local structure of the heme in the isolated alpha-, beta- and gamma-chains of the adult and fetal human hemoglobin are detected by XANES (X-ray absorption near-edge structure) spectroscopy. The ligand bonding angle to the iron ion in the ligated forms and the displacement of the Fe respect to the porphyrin plane in the deoxy forms are found to be different for each chain.