Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 130, Issue 12, Pages 3866-3877Publisher
AMER CHEMICAL SOC
DOI: 10.1021/ja076495a
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Funding
- NCRR NIH HHS [RR-01209, P41 RR001209] Funding Source: Medline
- NIGMS NIH HHS [GM50730, R01 GM050730-14, R01 GM050730, R29 GM050730] Funding Source: Medline
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S K-edge X-ray absorption, UV-vis absorption, magnetic circular dichroism (MCD), and resonance Raman spectroscopies are used to investigate the electronic structure differences among WT, M121 SeM, and C112SeC Pseudomonas aeruginosa (P.a) azurin. A comparison of S K-edge XAS of WT and M121SeM azurin and a Cull-thioether model complex shows that the 38% S character in the ground state wave function of the blue-copper (BC) sites solely reflects the Cu-S-Cys, bond. Resonance Raman (rR) data on WT and C112SeC azurin give direct evidence for the kinematic coupling between the Cu-S-Cys stretch and the cysteine deformation modes in WT azurin, which leads to multiple features in the rR spectrum of the BC site. The UV-vis absorption and MCD data on WT, M121SeM, and C112SeC give very similar C-0/D-0 ratios, indicating that the C-term MCD intensity mechanism involves Cu-centered spin-orbit coupling (SOC). The spectroscopic data combined with density functional theory (DFT) calculations indicate that S-Cys and Se-Cys have similar covalent interactions with Cu at their respective bond lengths of 2.1 and 2.3 angstrom. This reflects the similar electronegativites of S and Se in the thiolate/selenolate ligand fragment and explains the strong spectroscopic similarities between WT and C112SeC azurin.
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