کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
1942267 | 1052600 | 2013 | 9 صفحه PDF | دانلود رایگان |
![عکس صفحه اول مقاله: The fifth electron in the fully reduced caa3 from Thermus thermophilus is competent in proton pumping The fifth electron in the fully reduced caa3 from Thermus thermophilus is competent in proton pumping](/preview/png/1942267.png)
The time-resolved kinetics of membrane potential generation coupled to oxidation of the fully reduced (five-electron) caa3 cytochrome oxidase from Thermus thermophilus by oxygen was studied in a single-turnover regime. In order to calibrate the number of charges that move across the vesicle membrane in the different reaction steps, the reverse electron transfer from heme a3 to heme a and further to the cytochrome c/CuA has been resolved upon photodissociation of CO from the mixed valence enzyme in the absence of oxygen. The reverse electron transfer from heme a3 to heme a and further to the cytochrome c/CuA pair is resolved as a single transition with τ ~ 40 μs. In the reaction of the fully reduced cytochrome caa3 with oxygen, the first electrogenic phase (τ ~ 30 μs) is linked to OO bond cleavage and generation of the PR state. The next electrogenic component (τ ~ 50 μs) is associated with the PR → F transition and together with the previous reaction step it is coupled to translocation of about two charges across the membrane. The three subsequent electrogenic phases, with time constants of ~ 0.25 ms, ~ 1.4 ms and ~ 4 ms, are linked to the conversion of the binuclear center through the F → OH → EH transitions, and result in additional transfer of four charges through the membrane dielectric. This indicates that the delivery of the fifth electron from heme c to the binuclear center is coupled to pumping of an additional proton across the membrane.
► We have resolved kinetics of membrane potential generation by caa3 cytochrome oxidase.
► Single-turnover oxidation of the fully reduced enzyme by oxygen was studied.
► The number of charges translocated coupled to the different reaction steps were identified.
► Delivery of the fifth electron to the catalytic center is coupled to proton pumping.
Journal: Biochimica et Biophysica Acta (BBA) - Bioenergetics - Volume 1827, Issue 1, January 2013, Pages 1–9