Direct Voltammetric Observation of Redox Driven Changes in Axial Coordination and Intramolecular Rearrangement of the Phenylalanine-82-Histidine Variant of Yeast Iso-1-cytochrome c

Authors

Benjamin A. Feinberg, University of Wisconsin-Milwaukee
Xiangjun Liu, University of Illinois at Chicago
Michael D. Ryan, Marquette UniversityFollow
Abel Schejter, Tel-Aviv University
Chongyao Zhang, University of Wisconsin - Milwaukee
Emanuel Margoliash, Northwestern University

Document Type

Article

Language

eng

Publication Date

9-1-1998

Publisher

American Chemical Society

Source Publication

Biochemistry

Source ISSN

0006-2960

Abstract

Direct square-wave and cyclic voltammetric electrochemical examination of the yeast iso-1-cytochrome c Phe82His/Cys102Ser variant revealed the intricacies of redox driven changes in axial coordination, concomitant with intramolecular rearrangement. Electrochemical methods are ideally suited for such a redox study, since they provide a direct and quantitative visualization of specific dynamic events. For the iso-1-cytochrome c Phe82His/Cys102Ser variant, square-wave voltammetry showed that the primary species in the reduced state is the Met₈₀-Fe²⁺-His₁₈ coordination form, while in the oxidized state the His₈₂-Fe³⁺-His₁₈ form predominates. The addition or removal of an electron to the appropriate form of this variant serves as a switch to a new molecular form of the cytochrome. Using the 2 × 2 electrochemical mechanism, simulations were done for the cyclic voltammetry experiments at different scan rates. These, in turn, provided relative rate constants for the intramolecular rearrangement/ligand exchange and the equilibrium redox potentials of the participating coordination forms:  k_b,AC = 17 s^-1 for Met₈₀-Fe³⁺-His₁₈ → His₈₂-Fe³⁺-His₁₈ and k_f,BD > 10 s^-1 for His₈₂-Fe²⁺-His₁₈ → Met₈₀-Fe²⁺-His₁₈; E⁰‘ = 247 mV for Met₈₀-Fe^3+/2+-His₁₈ couple, E⁰‘ = 47 mV for His₈₂-Fe^3+/2+-His₁₈ couple, and E⁰‘ = 176 mV for the cross-reaction couple, His₈₂-Fe³⁺-His₁₈ + e^- → Met₈₀-Fe²⁺-His₁₈. Thermodynamic parameters, including the entropy of reaction, ΔS⁰‘_Rxn, were determined for the net reduction/rearrangement reaction, His₈₂-Fe³⁺-His₁₈ + e^- → Met₈₀-Fe²⁺-His₁₈, and compared to those for wild-type cytochrome, Met₈₀-Fe³⁺-His₁₈ + e^- → Met₈₀-Fe²⁺-His₁₈. For the Phe82His variant mixed redox couple, ΔS⁰‘_Rxn = −80 J/mol·K compared to ΔS⁰‘_Rxn = −52 J/mol·K for the wild-type cyt c couple without rearrangement. Comparison of these entropies indicates that the oxidized His₈₂-Fe³⁺-His₁₈ form is highly disordered. It is proposed that this high level of disorder facilitates rapid rearrangement to Met₈₀-Fe²⁺-His₁₈ upon reduction.

Comments

Biochemistry, Vol. 37, No. 38 (September 1998): 13091-13101. DOI.

Recommended Citation

Feinberg, Benjamin A.; Liu, Xiangjun; Ryan, Michael D.; Schejter, Abel; Zhang, Chongyao; and Margoliash, Emanuel, "Direct Voltammetric Observation of Redox Driven Changes in Axial Coordination and Intramolecular Rearrangement of the Phenylalanine-82-Histidine Variant of Yeast Iso-1-cytochrome c" (1998). Chemistry Faculty Research and Publications. 480.
https://epublications.marquette.edu/chem_fac/480