biostudies-otherUnknown247(2)Alleyne TAThe Biochemical journal475-84https://www.ebi.ac.uk/biostudies/studies/S-EPMC1148432Zinc 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.biostudies-otherEurope PMCWilson MTAlleyne TAfalseZinc cytochrome c fluorescence as a probe for conformational changes in cytochrome c oxidase.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.1987-01-01T00:00:00Z1987 Oct2019-08-04T07:19:01Z2019-08-04T07:19:01ZS-EPMC114843210.1042/bj2470475