Rapid Electron Transfer within the III-IV Supercomplex in Corynebacterium glutamicum. And the bo3 quinol oxidase of vitreoscilla.

The gram positive soil bacterium Corynebacterium glutamicum does not harbor any water-soluble cytochrome (cyt.) c. However, complex III of the respiratory chain has a di-heme cyt. c (called here cyt. bcc). In addition, the cyt. bcc-complex co-purifies with cytochrome c oxidase (CytcO), which suggests that the two respiratory enzymes form a supercomplex. Here, we investigated the kinetics of electron transfer within the putative cyt. bcc-CytcO supercomplex and in the CytcO alone. In the reaction of the reduced detergent-purified CytcO with O2 we observed the same sequence of events and kinetics as those observed previously with other A-type CytcOs. However, even though the reaction is associated with proton uptake from solution, we did not observe any pH dependence of the kinetics. The isolated cyt. bcc-CytcO complex displayed a quinol oxidation-O2 reduction activity of ~210 s 1, which is slightly faster than the CytcO activity (~180 s 1), indicating that electron transfer via the two C-hemes of cyt. bcc is not rate limiting for the overall quinol-oxidation activity. The data also indicate that one of the C-hemes of the cyt. bcc complex occupies a position near CuA. Furthermore, we show that during O2 reduction, electrons from the C-hemes of cyt. bcc were transferred to CuA over a time scale of at least 104 s 1. After oxidation, the C-hemes were re-reduced by the B-hemes over a time scale of ~6 ms. Taken together, the data indicate rapid intracomplex electron transfer between cyt. bcc and CytcO, via the diheme cyt. c, but without any water-soluble cyt. c.