Resonance Raman Excitation Profiles Indicate Multiple Cys → Cu Charge Transfer Transitions in Type 1 Copper Proteins

Jane Han, Thomas M. Loehr, Joann Sanders-Loehr, Y. Lu, Joan Selverstone Valentine, Bruce A. Averill

Research output: Contribution to journalArticlepeer-review

Abstract

Nitrite reductase (NiR) from Achromobacter cycloclastes and mutant yeast Cu-Zn Superoxide dismutase (with Cys substituted for His80 and Cu for Zn) have both been shown to contain type 1 Cu sites. However, they differ from other type 1 (blue) Cu proteins in that they are green: the absorption band at ∼460 nm is more intense than the one at ∼600 nm. Excitation within either of these absorption bands leads to resonance Raman (RR) spectra that are characteristic of type 1 Cu with a large number of peaks between 250 and 500 cm-1. The RR spectra of NiR and mutant SOD are thus indicative of a Cu-cysteinate chromophore with a short Cu-S bond distance (∼2.1 Å) and a coplanar cysteine moiety (Cu-Sγ-Cβ-Cα dihedral angle ∼180°). Since excitation within either the 460- or the 600-nm absorption band leads to a similar RR spectrum, both electronic transitions are likely to have (Cys)S → Cu(II) CT character. The RR enhancement profiles for azurin and pseudoazurin indicate that their low-intensity 460-nm absorption bands also have a Cys → Cu CT component. The occurrence of two different copper-cysteinate transitions at 460 and 600 nm helps to explain the fact that, although their relative absorptivities vary, the sum of ε460 and ε600 is fairly constant. Increased intensity at 460 nm appears to be associated with stronger binding of the axial ligand and a concomitant shift from a trigonal planar toward a more tetrahedral Cu site geometry.

Original languageEnglish (US)
Pages (from-to)4256-4263
Number of pages8
JournalJournal of the American Chemical Society
Volume115
Issue number10
DOIs
StatePublished - May 1 1993
Externally publishedYes

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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