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: To test the effect of the presence of the βXM motif alone, we introduced A181T to the protein in which the cysteines at positions 144 and 167 were not changed. With this mutation, cytochrome bc1 is functional in vivo (PS+ phenotype) (Table 1) and the optical difference spectra of purified complexes have the ascorbate-reducible component at 552 nm reminiscent of the presence of high potential cytochrome c (Fig. 2, dashed line). The shape of the spectra of cytochrome bc1 fully reduced with dithionite (Fig. 2, solid line) immediately suggests some similarities between A181T and A181T/disulfide-free cytochrome c1: in both spectra the 552 nm component of cytochrome c1 is less separated, in comparison to the wild type, from the component at 560 nm corresponding to cytochromes b. Even more significantly, the redox midpoint potential of A181T cytochrome c1 has a very close value to that of A181T/disulfide-free cytochrome c1 (235 vs. 228 mV) which, again, is about 100 mV lower than in the wild-type (Table 1, Fig. 3).
Affiliation: Department of Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, ul. Gronostajowa 7, 30-307 Kraków, Poland.