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Proceedings of the National Academy of Sciences of the United States of America logoLink to Proceedings of the National Academy of Sciences of the United States of America
. 1981 Jul;78(7):4190–4193. doi: 10.1073/pnas.78.7.4190

Identification of an electron transfer locus in plastocyanin by chromium(II) affinity labeling.

O Farver, I Pecht
PMCID: PMC319754  PMID: 6945578

Abstract

Cu(II)--plastocyanin from French beans (Phaseolus vulgaris) is reduced quantitatively by Cr(II)aq ions to give a substitution-inert Cr(III) adduct of Cu(I)--plastocyanin. Enzymatic proteolysis of this derivative by thermolysin led to the identification of the Cr(III) binding peptide. This contains four potential ligands for the metal ion: aspartate-42 and -44 and glutamate-43 and -45. In the three-dimensional fold of plastocyanin, this stretch is very close to tyrosine-83. The emission intensity and its pH dependence observed for the tyrosines in this tryptophan-devoid protein differ markedly in the Cr(III) adduct. That difference is interpreted as reflecting proximity and interaction between the latter metal ion and tyrosine-83. The distance between the copper center and the suggested Cr(III) binding site is approximately 12 A. The intervening region contains an array of highly invariant aromatic residues. These are proposed to be involved in the electron transfer process. A mechanism for that process is presented that involves interaction between the d electrons of the metal ions with d pi-pi* delocalization through a weakly coupled pi* system. The rationale of this electron transfer pathway for the reactivity of plastocyanin with inorganic redox agents is discussed.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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