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Protein matrix and dielectric effect in cytochrome c
1Department of Biochemistry and Molecular Biology, Dalhousie University, Nova Scotia, Canada B3H 4H7. cblouin@is2.dal.ca
The Journal of Biological Chemistry
|May 29, 2001
Summary
The protein matrix influences cytochrome c redox potential by affecting heme charge solvation. Conformational polarizability, not atomic properties, drives variability in dielectric susceptibility.
Area of Science:
- Biochemistry
- Protein Science
- Electrochemistry
Background:
- Cytochrome c's standard potential is modulated by its protein environment.
- Understanding protein dielectric properties is crucial for redox-active proteins.
Purpose of the Study:
- To investigate how the protein matrix affects the standard potential of a buried redox center in Saccharomyces cerevisiae cytochrome c.
- To determine the contribution of polypeptide solvation and dielectric properties to redox potential shifts.
Main Methods:
- Utilized mutants and chemical derivatives of Saccharomyces cerevisiae cytochrome c.
- Analyzed changes in redox potential (Delta E(m)(0)') based on solvation and dielectric properties.
- Investigated entropic factors by substituting specific amino acids (Asn52 and Tyr67).
Main Results:
- Apparent dielectric constants showed variability, especially when using free energy changes (Delta G(0)redox).
- Consistent results were obtained using enthalpy changes (Delta H(0)redox), with a measured epsilon(Delta Delta)(H)(redox) of 19 +/- 6.
- Eliminating the heme crevice hydrogen bond network in double mutants did not significantly alter the redox entropy (Delta S(redox)) compared to wild type.
Conclusions:
- Variability in dielectric susceptibility is attributed to conformational polarizability, not solely atomic properties.
- A consistent hydrogen bond network exhibits similar polarizability to an apolar matrix.
- Protein dielectric properties are complex and influenced by factors beyond simple atomic composition.