NMR redox studies of flavocytochrome c3 from Shewanella frigidimarina

Flavocytochrome c3 is a periplasmic fumarate reductase with Mr 63.8 kDa, isolated from Shewanella frigidimarina NCIMB400. NMR spectroscopy was tested for its potential to elucidate the oxidation profile of each of the four haem groups in the enzyme, using the strategy developed previously to perform the thermodynamic characterization of small tetrahaem cytochromes (FEBS Lett. 314 (1992) 155). This work shows that, despite the large size of the protein, 2D-NMR NOESY experiments can be used to obtain the network of chemical exchange connectivities, between the signals of specific haem groups in sequential oxidation stages.