J. Biol. Chem., Vol. 263, Issue 8, 3588-3591, 03, 1988
An electron nuclear double resonance investigation of redox-induced electronic structural change at CuA2+ in cytochrome c oxidase
C Fan, JF Bank, RG Dorr and CP Scholes
Department of Physics, State University of New York at Albany 12222.
We measured an electronic change at cysteine ligand(s) of the CuA2+ center
brought on by reduction of other metal centers within cytochrome c oxidase,
notably cytochrome a. This change specifically manifested itself as a
modification in magnetic hyperfine coupling to the beta- protons of the
beta-carbons adjacent to the cysteine sulfur in the CuA2+ coordination
sphere. The electron nuclear double resonance ENDOR signals of these
beta-protons had previously been assigned through study of selectively
deuterated yeast oxidase. In the present study the ENDOR signals of the
CuA2+ center were compared from the following forms of oxidase: resting
(a3+.CuA2+.a3+3.CuB2+); mixed valence, 2- electron-reduced CO-ligated
oxidase (a3+.CuA2+.a2+3CO.CuB+), and a more completely reduced
mixed-valence CO-ligated oxidase. In agreement with previous studies on
3-electron-reduced oxidase, the latter more completely reduced oxidase
showed cytochrome a preferentially reduced with respect to CuA, implying
that the majority of paramagnetic CuA2+ centers had reduced cytochrome a
partners. The ENDOR-resolved splitting of the beta-proton hyperfine
features substantially decreased in going from the first two more oxidized
forms to the more fully reduced latter form. Thus, the electronic structure
of the CuA2+ center specifically monitored by hyperfine couplings to
cysteine protons changed in response to a reductive event elsewhere in the
protein. This structural change may correlate with the anticooperative
redox interaction recently reported between cytochrome a and CuA.
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