Redox Thermodynamics of Cytochromes c Subjected to Urea Induced Unfolding

S. Monari, A. Ranieri, G. Di Rocco, G. van der Zwan, S. Peressini, C. Tavagnacco, D. Millo, M. Borsari

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Abstract

The thermodynamics of the electron transfer (ET) process for beef heart and yeast cytochromes c and the Lys72Ala/Lys73Ala/Lys79Ala mutant of the latter species subjected to progressive urea-induced unfolding was determined electrochemically. The results indicate the presence of at least three protein forms which were assigned to a low-temperature and a high-temperature His-Met intermediate species and a bis-histidinate form (although the presence of a His-Lys form cannot be excluded). The much lower E°' value of the bis-histidinate conformer as compared to His-Met ligated species is largely determined by the enthalpic contribution induced by axial ligand substitution. The biphasic E°' versus T profile for the His-Met species is due to a difference in reduction entropy between the conformers at low and high temperatures. Enthalpy-entropy compensation phenomena for the reduction reaction at varying urea concentration for all the forms of the investigated cytochromes c were addressed and discussed. © 2009 Springer Science+Business Media B.V.
Original languageEnglish
Pages (from-to)2181-2190
JournalJournal of Applied Electrochemistry
Volume39
DOIs
Publication statusPublished - 2009

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