Visualizing changes in electron distribution in coupled chains of cytochrome bc(1) by modifying barrier for electron transfer between the FeS cluster and heme c(1).
Bottom Line: This establishes effective means to modify a barrier for electron transfer between the FeS cluster and heme c(1) without breaking disulfide.In the non-inhibited system no such differences were observed.We explain the results using a kinetic model in which a shift in the equilibrium of one reaction influences the equilibrium of all remaining reactions in the cofactor chains.
Affiliation: Department of Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, ul. Gronostajowa 7, 30-307 Kraków, Poland.Show MeSH
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Mentions: The full cytochrome c re-reduction in the absence of any inhibitor consumes electrons from the pre-reduced FeS cluster and then from quinols that are oxidized at the Qo site in a coupled reaction that delivers the second quinol-born electron to the b-chain. A completeness of this reaction is a consequence of the unperturbed outflow of electrons from hemes b to the Qi site and further down to the Q pool. In another words, a completion of two reactions of QH2 oxidation at the Qo site secured by an immediate removal of electrons from hemes b leaves all cofactors in the c-chain (including the FeS cluster) fully saturated with electrons. The reaction is driven to completion even when heme c1 has potential 100 mV lower than Em of FeS in the mutant (Fig. 6, no inhibitor panel). This is consistent with the observations that the Em of heme c1 can be lowered within this range without affecting the overall electron flow through the c-chain [27,44]. In fact, the difference in Ems between heme c1 and the FeS cluster can be as much as 180 mV and the enzyme still muster enough electron transfer through cytochrome bc1 to support its functionality .
Affiliation: Department of Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, ul. Gronostajowa 7, 30-307 Kraków, Poland.