Redox-Bohr effect in the nine haem cytochrome from Desulfovibrio desulfuricans 27774

Redox titrations followed by visible spectroscopy were performed at various pH values with the nine-haem cytochrome c from Desulfovibrio desulfuricans ATCC 27774 (Dd27774). Macroscopic midpoint reduction potentials of the haems and pKa ox and pKa red values of acid–base centres that interact with the redox centres were estimated by using a thermodynamic model, in which the haems are grouped in three sets, and two acid–base centres are considered. The results show that this cytochrome displays redox-Bohr effects in the physiological pH range and that electrostatic effects dominate the macroscopic interactions between the acid–base and redox centres.