We have here investigated the dissociation kinetics of the His side chains axially ligated to the heme-iron in the ferric (1-56 residues) N-fragment of horse cyt c. The ligand deligation induced by acidic pH-jump occurs as a biexponential process with different pre-exponential factors, consistent with a structural heterogeneity in solution and the presence of two differently coordinated species. In analogy with GuHCl-denatured cyt c, our data indicate the presence in solution of two ferric forms of the N-fragment characterized by bis-His coordination, as summarized in the following scheme: His18-Fe(III)-His26 (-->)(<--) His18-Fe(III)-His33. We have found that the pre-exponential factors depend on the extent of the pH-jump. This may be correlated with the different pK(a) values shown by His26 and His33; due to steric factors, His26 binds to the heme-Fe(III) less strongly than His33, as recently shown by studies on denatured cyt c. Interestingly, the two lifetimes are affected by temperature but not by the extent of the pH-jump. The lower pK(a) for the deligation reaction required the use of an improved laser pH-jump setup, capable of inducing changes in H+ concentration as large as 1 mM after the end of the laser pulse. For the ferric N-fragment, close activation entropy values have been determined for the two histidines coordinated to the iron; this result significantly differs from that for GuHCl-denatured cyt c, where largely different values of activation entropy were calculated. This underlines the role played by the missing segment (residues 57-104) peptide chain in discriminating deligation of the "nonnative'' His from the sixth coordination position of the metal.
Abbruzzetti S., V.C. (2004). Kinetics of histidine dissociation from the heme Fe(III) in N-fragment (residues 1-56) of cytochrome c. PROTEIN JOURNAL, 23(8), 519-527.
|Tipologia:||Articolo su rivista|
|Citazione:||Abbruzzetti S., V.C. (2004). Kinetics of histidine dissociation from the heme Fe(III) in N-fragment (residues 1-56) of cytochrome c. PROTEIN JOURNAL, 23(8), 519-527.|
|IF:||Con Impact Factor ISI|
|Settore Scientifico Disciplinare:||Settore BIO/10|
|Revisione (peer review):||Sì, ma tipo non specificato|
|Digital Object Identifier (DOI):||http://dx.doi.org/10.1007/s10930-004-7879-x|
|Stato di pubblicazione:||Pubblicato|
|Data di pubblicazione:||2004|
|Titolo:||Kinetics of histidine dissociation from the heme Fe(III) in N-fragment (residues 1-56) of cytochrome c|
|Autori:||Abbruzzetti S., Viappiani C., Sinibaldi F., Santucci R.|
|Appare nelle tipologie:||01 - Articolo su rivista|