Zinc cytochrome c forms tight 1:1 complexes with a variety of derivatives of cytochrome c oxidase. On complex-formation the fluorescence of zinc cytochrome c is diminished. Titrations of zinc cytochrome c with cytochrome c oxidase, followed through the fluorescence emission of the former, have yielded both binding constants (K approximately 7 x 10(6) M-1 for the fully oxidized and 2 x 10(7) M-1 for the fully reduced enzyme) and distance information. Comparison of steady-state measurements obtained by absorbance and fluorescence spectroscopy in the presence and in the absence of cyanide show that it is the reduction of cytochrome a and/or CuA that triggers a conformational change: this increases the zinc cytochrome c to acceptor (most probably cytochrome a itself) distance by some 0.5 nm. Ligand binding to the fully oxidized or fully reduced enzyme leaves the extent of fluorescence quenching unchanged, whereas binding of cyanide to the half-reduced enzyme (a2+CuA+CuB2+-CN(-)-a3(3+)) enhances fluorescence emission relative to that for the fully reduced enzyme, implying further relative movement of donor and acceptor.
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Research Article| October 15 1987
Zinc cytochrome c fluorescence as a probe for conformational changes in cytochrome c oxidase
T A Alleyne ;
Biochem J (1987) 247 (2): 475–484.
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T A Alleyne, M T Wilson; Zinc cytochrome c fluorescence as a probe for conformational changes in cytochrome c oxidase. Biochem J 15 October 1987; 247 (2): 475–484. doi: https://doi.org/10.1042/bj2470475
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