Redox and redox-Bohr cooperativity studies in a new tetrahaem cytochrome isolated from Shewanella frigidimarina

During anaerobic growth the facultatively anaerobic bacterium, Shewanella frigidimarina NCIMB400, Sf produces a small tetrahaem cytochrome (86 residues) that is involved in electron transfer to Fe(III), a terminal respiratory oxidant of this microorganism ~. A 3D structure model of the reduced form of this cytochrome was determined by NMR ~. The haem core architecture of Sftetrahaem cytochrome differs from that found in all small tetrahaem cytochromes c3 so far isolated from strict anaerobes, but has some similarity with to the N-terminal cytochrome domain of the flavocytochrome c~ isolated from Sf 3 Based on the 3D structure model and in NMR redox titrations it was possible to assign the order of oxidation of the haems 2. NMR and visible redox titrations were also performed at different pH values to determine both the haem potentials, as well as the redox and redox-Bohr cooperativities in the Sftetrahaem cytochrome