Electrostatic Analysis of the Midpoints of the Cofactors in the Reaction Center Protein of Rp.viridis
The relative midpoints of the cofactors in the reaction center protein (RC) from Rp. viridis were calculated by solving the Poisson-Boltzmann equation with a finite difference algorithm. This yields the electrostatic potential throughout the RC which can provide the energetic cost of oxidizing or reducing each site. For the 4 hemes of the bound cytochrome subunit the calculations are in quite good agreement with the experimentally determined relative heme midpoints. The success of the method allows the factors that generate the differences in their in situ electrochemistry to be identified. In order of importance these appear to be: (1) the distribution of charged residues throughout the protein; (2) the perturbation of the midpoint of the high potential hemes by the oxidized lower potential sites; (3) the nature of the axial ligands; (4) differences in the stabilization of the charged heme by solvent. Preliminary calculations were also carried out on the cofactors within the RC.
KeywordsSolvation Energy Partial Charge Axial Ligand Electron Transfer Rate Reaction Center Protein
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