On the energetics of conformational changes and pH dependent redox behaviour of electron transfer proteins

Calculations of the electrostatic interaction energies for four metalloproteins that carry out electron transfer are reported. Each protein has a pH dependent redox potential from which the measured electrostatic interaction energy is obtained. The calculations were made using the X-ray structure coordinates and a semimacroscopic model of the interactions. For cytochrome c-551 and HIPIP the calculated and observed interaction energies were found to be approximately the same, in agreement with the fact that significant conformational changes do not accompany the ionisations. For cytochrome c2 and azurin, however, major differences were found between the calculated and observed values. These are accounted for primarily by the occurrence of significant conformational changes accompanying the ionisations. The reorganisation energies for these conformational changes are approximately 7.0 and approximately 11.1 kJ.mol-1, respectively.