We used hybrid fusion bc 1 complex to test inter-monomer electron transfer in vivo.
Cross-inactivated complexes were able to sustain photoheterotrophic growth.
Inter-monomer electron transfer supports catalytic cycle in vivo.
bc 1 dimer is functional even when cytochrome b subunits come from different species.
Electronic connection between Q o and Q i quinone catalytic sites of dimeric cytochrome bc 1 is a central feature of the energy-conserving Q cycle. While both the intra- and inter-monomer electron transfers were shown to connect the sites in the enzyme, mechanistic and physiological significance of the latter remains unclear. Here, using a series of mutated hybrid cytochrome bc 1-like complexes, we show that inter-monomer electron transfer robustly sustains the function of the enzyme in vivo, even when the two subunits in a dimer come from different species. This indicates that minimal requirement for bioenergetic efficiency is to provide a chain of cofactors for uncompromised electron flux between the catalytic sites, while the details of protein scaffold are secondary.