Biomedical subjects
Publications and source records attributed to A Bianconi.
We report the stopping power of molecular hydrogen for antiprotons of kinetic energy above the maximum (approximately 100 keV) with the purpose of comparing with the proton one. Our result is consistent with a positive difference in antiproton-proton stopping powers above approximately 250 keV and with a maximum difference between the stopping powers of 21%+/-3% at around 600 keV.
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We present the results of a comparative study of the binding of carbon monoxide to myoglobin in glycerol/buffer solution with different concentrations of guanidine hydrochloride, under extended illumination over the temperature range 30-80 K. The changes in the Soret band indicate that the folding state of the protein is a key parameter in determining the photodissociation process and the relaxation rate of the protein.
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.
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We have measured the x-ray absorption near edge structure (XANES) spectra of the enzyme tyrosinase from the mushroom Agaricus bisporus in solution in the oxy and deoxy forms. The spectra, obtained under the same conditions as the analogous forms of mollusc hemocyanin (Hc), show that the oxidation state of copper changes from Cu(II) (oxy form) to Cu(I) (deoxy form), and the copper active site(s) of A. bisporus tyrosinase in solution undergoes the same main conformational changes as Hc. We have applied the multiple scattering theory to simulate the XANES spectra of various alternative geometries of the copper site, accounting for the residual differences between Hc and tyrosinase. While oxy-Hc is reasonably fitted only by the pseudo-square-pyramidal geometry reported by its crystallographic data, oxytyrosinase can be fitted, starting from the Hc coordinates, either by distortions toward a pseudo-tetrahedral geometry, with inequivalent copper sites, or by an apically distorted square-pyramidal geometry (with an elongation of the apical distance of no more than 0.2 A).
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The Fe K-edge X-ray absorption near-edge structure (XANES) spectra of two irreversible human hemichromes, spontaneously formed from HbA and HbMetSO (a hemoglobin derivative, where MetD6(55)beta has been previously oxidized to sulfoxide by chloramine T) were determined. The results show that the hemichrome from HbMetSO is characterized by the distal histidyl imidazole moved within the bonding distance of the heme iron. Such structure is different from that of the hemichrome spontaneously produced from native human hemoglobin, which probably has a hydroxide group as sixth heme ligand.
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We report experimental evidence that the pH value of the micro-environment of the protein is the key for the conformational changes of transferrin, rather than the ligated for unligated state of the binding sites. The "open" and "closed" conformation of protein, suggested by X-ray crystallography in static condition, is triggered by the pH value and the effect is independent of the metal ion being transported. We propose a simple description of the structure-function relationship that allows this protein to deliver, in particular, iron or aluminum ions in the biological cycle.