title: Comparison of the X-ray absorption properties of the binuclear active site of molluscan and arthropodan hemocyanins.
abstract: The structural characteristics of oxy- and deoxy-hemocyanins have been investigated using X-ray absorption spectroscopy both in the near-edge (XANES) and for the first shell contribution in the EXAFS region. Several arthropodan and molluscan hemocyanins have been studied in order to trace the inter- and intra-phyla differences. The XANES spectra of oxy-hemocyanins of the different species are remarkably similar, consistent with a very strongly conserved co-ordination geometry of the copper active site. In contrast, small but significant differences are observed between the deoxy-forms of arthropodan and molluscan proteins. In particular, the XANES spectra of deoxy-arthropodan hemocyanins (with the exception of L. polyphemus Hc) show a more intense edge feature at approximately 8983 eV. This difference is tentatively assigned to a more planar geometry of the copper-ligands system in the arthropodan rather than in the molluscan proteins. The first shell analysis of the EXAFS modulation is consistent with the presence of n=3Nepsilon(2) imidazole nitrogens at an average distance of 1.92 +/- 0.03 A from copper in all the deoxy-hemocyanins investigated. Binding of dioxygen results for all hemocyanins in the increase of the number of first shell back-scattering atoms to n=5 with average distances of 1.93 A. Alternatively, by separating the contribution of Nepsilon(2) imidazole nitrogens and of peroxide O-atoms, n=3 ligands at 1.98 +/- 0.03 A and n=2 ligands at 1.87 +/- 0.03 A are found.
authors.affiliation: Dipartimento di Biologica, Università degli studi di Padova, via U. Bassi, Padova, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Sabatucci
authors.forename: I
authors.initials: I
authors.lastname: Ascone
authors.forename: L
authors.initials: L
authors.lastname: Bubacco
authors.forename: M
authors.initials: M
authors.lastname: Beltramini
authors.forename: DiP
authors.initials: D
authors.lastname: Muro
authors.forename: B
authors.initials: B
authors.lastname: Salvato
mesh_terms: D000818:Animals; D001181:Arthropods / Q000378:metabolism*; D001665:Binding Sites / Q000502:physiology; D003300:Copper / Q000737:chemistry / Q000378:metabolism*; D006433:Hemocyanins / Q000737:chemistry* / Q000378:metabolism; D008974:Mollusca / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism*; D011485:Protein Binding / Q000502:physiology; D013045:Species Specificity; D013057:Spectrum Analysis / Q000379:methods; D014965:X-Rays
chemical_list: D003300:Copper; D006433:Hemocyanins; D010100:Oxygen