Optically active cobalt(II) complexes are used as reducing agents in the electron-transfer reaction involving horse heart cytochrome c. Analysis of the circular dichroism (CD) spectra of reaction products indicates that the corresponding cobalt(III) species of both enantiomers of [Co) are partly attached to the protein during electron transfer by coordination to an imidazole unit of one of the histidine residues. His-26 and His-33 are both solvent exposed, and the results suggest that one of these histidine residues acts as a bridge in the electron transfer to and from the haem iron of cytochrome c. The reaction is enantioselective: the ratio of the relative reactivity at 15 8C is 2.9 in favour of the R,R-enantiomer. A small induced CD activity in the haem chromophore reveals that some structural changes in the protein occur consecutively with the binding of the cobalt(III) complex.
Key indicatorsSingle-crystal X-ray study T = 173 K Mean (C-C) = 0.004 Å R factor = 0.041 wR factor = 0.104 Data-to-parameter ratio = 6.5For details of how these key indicators were automatically derived from the article, see
Key indicatorsSingle-crystal X-ray study T = 173 K Mean (C-C) = 0.001 Å R factor = 0.037 wR factor = 0.099 Data-to-parameter ratio = 14.2 For details of how these key indicators were automatically derived from the article, see
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