An EPR signal from the "invisible" copper of cytochrome oxidase. |
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Authors: | C H Seiter S G Angelos R A Perreault |
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Institution: | Department of Chemistry, University of Southern California Los Angeles, California 90007, USA |
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Abstract: | Sulfide is both an inhibitor and a slow reductant of oxidized cytochrome oxidase. When the enzyme is exposed to sulfide for short times (one minute or less) and frozen, the resultant electron paramagnetic resonance (EPR) signals show clearly: low spin heme a, low spin heme a3, the usual “EPR detectable” Cu2+ signal (g⊥ = 2.17, g⊥ = 2.03), and a new Cu2+ signal superimposed on the same region, with (g⊥ ~ 2.19, g⊥ = 2.05). This new signal presumably arises because the antiferromagnetic coupling postulated to exist between the iron atom of heme a3 and this copper is disrupted when heme a3 is driven to a low spin state by sulfide. The implications of this result with respect to models of the O2-binding site and redox geometry of oxidase are briefly discussed. |
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