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Conformational and redox equilibria and dynamics of cytochrome c immobilized on electrodes via hydrophobic interactions
Citation key ISI:000175488500034
Author Rivas, L and Murgida, D H and Hildebrandt, P
Pages 4823-4830
Year 2002
ISSN 1520-6106
DOI 10.1021/jp014175m
Address 1155 16TH ST, NW, WASHINGTON, DC 20036 USA
Journal J. Phys. Chem. B
Volume 106
Number 18
Month MAY 9
Publisher AMER CHEMICAL SOC
Abstract Surface enhanced resonance Raman (SERR) spectroscopy was employed to study structure and dynamics of cytochrome c (Cyt-c) immobilized on Ag electrodes that were coated with self-assembled monolayers (SAM) of n-alkanethiols HS-(CH2)(n)-CH3. Cyt-c is bound to these electrodes by hydrophobic interactions most likely via the peptide segment 81-85 that may partially penetrate into the monolayers. The immobilized proteins are partially converted to the conformational state B2 that exhibits a different heme pocket structure and coordination configuration than the native state B1. The B2/B1 conformational equilibrium. which can also be induced by binding to electrodes coated with omega-carboxyl alkanethiols (Murgida, D. H.; Hildebrandt, P. J. Phys. Chem. B 2001, 105, 1578), is potential-dependent with the B1 state prevailing at potentials < -0.3 V. On hydrophobic coatings, the equilibrium constant is largely independent of the thickness of the SAM except for HS-CH2CH3 coatings, which do not allow integration of the apolar peptide segment. Using time-resolved SERR spectroscopy, the dynamics of the conversion from the ferric B2 state to the ferrous B I state were analyzed. The underlying conformational transitions are potential-dependent and involve a fast step (ca. 10(4)-10(5) s(-1)) that may either be the formation of the ferric B2 state or the back-conversion to the ferrous B I state. The conformational transitions are substantially faster than those observed for electrostatically bound Cyt-c where rearrangements of the hydrogen-bonding network in the protein are associated with high electric field induced activation barriers. For the hydrophobically bound Cyt-c, the fast conformational transitions proceed on the same time scale as the intermolecular electron transfer between Cyt-c and its natural partner cytochrome c oxidase and may play a role in the biological process.
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