title: pH-dependent redox and CO binding properties of chelated protoheme-L-histidine and protoheme-glycyl-L-histidine complexes.
abstract: The pH dependence of redox properties, spectroscopic features and CO binding kinetics for the chelated protohemin-6(7)-L-histidine methyl ester (heme-H) and the chelated protohemin-6(7)-glycyl-L-histidine methyl ester (heme-GH) systems has been investigated between pH 2.0 and 12.0. The two heme systems appear to be modulated by four protonating groups, tentatively identified as coordinated H(2)O, one of heme's propionates, N(epsilon) of the coordinating imidazole, and the carboxylate of the histidine residue upon hydrolysis of the methyl ester group (in acid medium). The pK (a) values are different for the two hemes, thus reflecting structural differences. In particular, the different strain at the Fe-N(epsilon) bond, related to the different length of the coordinating arm, results in a dramatic alteration of the bond strength, which is much smaller in heme-H than in heme-GH. It leads to a variation in the variation of the pKa for the protonation of the N(epsilon) of the axial imidazole as well as in the proton-linked behavior of the other protonating groups, envisaging a cross-talk communication mechanism among different groups of the heme, which can be operative and relevant also in the presence of the protein matrix.
authors.affiliation: Department of Molecular, Cellular and Animal Biology, University of Camerino, Via F. Camerini 2, 62032 Camerino, Italy.
authors.forename: Giampiero
authors.initials: G
authors.lastname: De Sanctis
authors.forename: Giovanni Francesco
authors.initials: GF
authors.lastname: Fasciglione
authors.forename: Stefano
authors.initials: S
authors.lastname: Marini
authors.forename: Federica
authors.initials: F
authors.lastname: Sinibaldi
authors.forename: Roberto
authors.initials: R
authors.lastname: Santucci
authors.forename: Enrico
authors.initials: E
authors.lastname: Monzani
authors.forename: Corrado
authors.initials: C
authors.lastname: Dallacosta
authors.forename: Luigi
authors.initials: L
authors.lastname: Casella
authors.forename: Massimo
authors.initials: M
authors.lastname: Coletta
mesh_terms: D002248:Carbon Monoxide / Q000737:chemistry*; D002614:Chelating Agents / Q000737:chemistry; D004151:Dipeptides / Q000737:chemistry*; D006418:Heme / Q000737:chemistry*; D006639:Histidine / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D015394:Molecular Structure; D019906:Nuclear Magnetic Resonance, Biomolecular; D010084:Oxidation-Reduction; D013816:Thermodynamics
chemical_list: D002614:Chelating Agents; D004151:Dipeptides; C027787:glycylhistidine; D006418:Heme; D006639:Histidine; D002248:Carbon Monoxide