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- W1992502546 abstract "Abstract A prevailing view of cytochrome c -oxidase's mode of action is that the cytochrome a moiety of the oxidase is first reduced by electrons from ferrocytochrome c , and then electron transfer occurs from cytochrome a to cytochrome a 3 and finally to oxygen [1]. We address the question of how this functional interaction is related to structural perturbation of the a 3 center by the a center or to simple proximity of the two centers. We have investigated this problem with NO complexed to heme a 3 in fully reduced oxidase ( a 2+ · Cu 1+ a · a 2+ 3 · Cu 1+ a3 ) and with NO and CO complexed to heme a 3 in a mixed valence (MV) state oxidase ( a 3+ · Cu 2+ a · a 2+ 3 · Cu 1+ a3 ). Bovine cardiac cytochrome c oxidase was prepared by methods of Refs. 2 and 3. Fully reduced and mixed valence complexes were prepared in a modified Thunberg cell under strictly anaerobic conditions. EPR (electron paramagnetic resonance) spectra were recorded under non-saturating microwave powers with a Bruker ER 420 (9.0 - 9.8 GHz) spectrometer over a 12–77 temperature range. The EPR of nitrosylferrocytochrome a 3 ( i.e. , a 3 NO in both fully reduced and MV forms showed detailed hyperfine structure from nitrogen nuclei of NO and proximal histidine. The EPR features encompassed a g-value range of g x , g z , g y = 2.09, 2.006, 1.98. The MV- a 3 -NO form, but not the fully reduced, showed additional temperature-dependent spectral changes setting in below 40 K. The most striking change occurred near g = 2.09 and smaller line-broadening changes occurred near g = 2.00. In MV- a 3 -NO there thus appears to be an internal magnetic interaction that shows rapid, temperature-dependent fluctuations down to 40 K but below 40 K slows sufficiently to allow resolution by EPR. This internal interaction has a magnitude of 12, 1.5, and 5 Gauss at g x , g z and g y respectively. At present we have two separate explanations for the phenomenon which both indicate a - a 3 interaction. Either, as a result of redox changes at cytochrome a , a changed ligand-binding environment, which has conformations that rapidly convert down to 40 K, occurs at NO-liganded cytochrome a 3 . Or, a dipolar spin-spin interaction occurs between the No-liganded and a paramagnetic metal center in cytochrome a ; this spin-spin interaction is modulated by temperature-dependent spin-lattice relaxation (which we have independently measured) of the center in cytochrome a . If the latter explanation is correct, the distance between a 3 -NO and the interacting center in cytochrome a can be estimated at 15 A, and the more likely interacting center in cytochrome a predicted to be heme a ." @default.
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- W1992502546 date "1983-01-01" @default.
- W1992502546 modified "2023-09-27" @default.
- W1992502546 title "EPR-detected interaction between cytochrome a3 and cytochrome a in cytochrome c oxidase" @default.
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- W1992502546 doi "https://doi.org/10.1016/s0020-1693(00)95151-x" @default.
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