Electrochemical Evidence of the Redox-controlled Ligand Exchange of the Heme in the CO-sensing Transcriptional Activator CooA

The CO-sensing transcriptional activator CooA contains the six-coordinate, low-spin protoheme as a CO sensor. In this work, the reduction and oxidation midpoint potentials of CooA were determined by electrochemical redox titrations, which were -320 mV and -260 mV (vs. NHE), respectively. The different midpoint potentials provide evidence for exchange of the heme axial ligand during the change in the redox state of the heme.