Probing protein electrostatic interactions through temperature/reduction potential profiles |
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Authors: | Roberto P Christen Spyros I Nomikos E T Smith |
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Institution: | (1) Department of Chemistry, Florida Institute of Technology, 150 West University Boulevard, Melbourne, FL 32901-6988, USA, US |
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Abstract: | The change in the equilibrium reduction potentials of the iron-sulfur proteins, Pyrococcus furiosus rubredoxin and P. furiosus ferredoxin, and heme protein, horse cytochrome c, has been calculated as a function of temperature using a numerical solution to the Poisson-Boltzman equation. Working curves
for different internal dielectric constants were generated to best reproduce experimental observation. Based on a comparison
of the experimental and simulated change in reduction potential with temperature, it is concluded that the dielectric constant
of proteins is temperature-dependent and varies from protein to protein. For example, the temperature-dependent reduction
potential of cytochrome c can only be simulated using a different temperature-dependent dielectric constant for each oxidation state, but this was
not the case for rubredoxin or ferredoxin. The role of changes in ionization states of cytochrome c at alkaline pHs, where the reduction potential is known to be pH-dependent at room temperature, is also discussed in terms
of electrostatic interaction energies as a function of temperature. It appears that temperature/reduction potential profiles
may provide a direct method for measuring relative changes in internal protein dielectric constants.
Received: 29 April 1996 / Accepted: 1 August 1996 |
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Keywords: | Iron sulfur Cytochrome c Reduction potential Dielectric constant Temperature dependence |
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