pH-dependent redox and CO binding properties of chelated protoheme-L-histidine and protoheme-glycyl-L-histidine complexes.
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.
De Sanctis
Giampiero
G
Department of Molecular, Cellular and Animal Biology, University of Camerino, Via F. Camerini 2, 62032 Camerino, Italy.
Fasciglione
Giovanni Francesco
GF
Marini
Stefano
S
Sinibaldi
Federica
F
Santucci
Roberto
R
Monzani
Enrico
E
Dallacosta
Corrado
C
Casella
Luigi
L
Coletta
Massimo
M
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
D002614:Chelating Agents; D004151:Dipeptides; C027787:glycylhistidine; D006418:Heme; D006639:Histidine; D002248:Carbon Monoxide