On the inter-monomer electron transfer in cytochrome bc1

Cytochrome bc₁ is a structural and functional homodimer. The catalytically-relevant inter-monomer electron transfer has been implicated by a number of experiments, including those based on analyses of the cross-dimer mutated derivatives. As some of the original data on these derivatives have recently been questioned, we extend kinetic analysis of these mutants to confirm the enzymatic origin of the observed activities and their relevance in exploration of conditions that expose electron transfer between the monomers. While obtained data consistently implicate rapid inter-monomer electron equilibration in cytochrome bc₁, the mechanistic and physiological meaning of this equilibration is yet to be established.