Kinetics of electron transfer in strain BH6

The kinetics for a control strain, BC17C, with the bc1-complex genes fbc expressed from a plasmid, and for strain BH6, in which a similar plasmid is used to express a cytochrome b with a His6 extension at the C-terminus.

Note that the kinetics in the two strains are similar either when the quinone pool is oxidized (at 200 mV) or partly reduced (~30% reduced at 100 mV). The difference between the two strains is in the relative stoichiometries of the components of the chain. This can be seen from the amplitudes of the traces after four flashes in the presence of antimycin. The extintion coefficients for cyt bH (measured at 561-569 nm) and cyt ct (measured at 551-542 nm) are similar (~20, and that for the reaction center (measured at 542 nm) is about half this value (~10 The traces show stoichiometric ratios for RC:c2:bc1-complex close to the "normal" 2:1:1 for BC17C, but about 2:1:3 for BH6, showing the substantial overexpression of the bc1-complex. 

Redox tritration and spectra of the b-type cytochromes of strain BH6. Note that the potentials and spectra are essentially the same as in wild-type.

Tony Crofts