We propose that hemesbin this cytochrome and in other membranous cytochromesbact as electronic connectors for the catalytic sites with no fine tuning in ΔEm_b required for efficient cross-membrane electron transfer.  We link this concept with a natural flexibility in occurrence of several thermodynamic configurations of the direction of electron flow and the direction of the gradient of potential in relation to the vector of the electric membrane potential.
THERM