A new method is presented that makes it possible to inject electrons rapidly into redox-active proteins by means of a short light flash. Reduced carboxymethylated cytochrome c (CmCyt c) with carbon monoxide bound to the heme iron is mixed with the oxidized acceptor protein. Upon rapid photodissociation of CO the apparent redox potential of CmCyt c drops, resulting in electron transfer to the electron acceptor. In this study we have used mitochondrial cyto- chrome c oxidase as the acceptor protein, but the method also can be used to investigate electron transfer to other proteins that can interact with cytochrome c. In principle, it can be used with any redox protein into which a CO binding site at the heme iron can be engineered.
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