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Electron Flow through Nitrotyrosinate in Pseudomonas aeruginosa Azurin
- Warren, Jeffrey
J., Herrera, Nadia, Hill, Michael G., Winkler, Jay R., Gray, Harry B.
- Journal of the American Chemical Society 2013 v.135 no.30 pp. 11151-11158
- Pseudomonas aeruginosa, copper, electron transfer, histidine, oxidation, spectroscopy
- We have designed ruthenium-modified Pseudomonas aeruginosa azurins that incorporate 3-nitrotyrosine (NO₂YOH) between Ru(2,2′-bipyridine)₂(imidazole)(histidine) and Cu redox centers in electron transfer (ET) pathways. We investigated the structures and reactivities of three different systems: RuH107NO₂YOH109, RuH124NO₂YOH122, and RuH126NO₂YOH122. RuH107NO₂YOH109, unlabeled H124NO₂YOH122, and unlabeled H126NO₂YOH122 were structurally characterized. The pKₐ’s of NO₂YOH at positions 122 and 109 are 7.2 and 6.0, respectively. Reduction potentials of 3-nitrotyrosinate (NO₂YO–)-modified azurins were estimated from cyclic and differential pulse voltammetry data: oxidation of NO₂YO–122 occurs near 1.1 versus NHE; oxidation of NO₂YO–109 is near 1.2 V. Our analysis of transient optical spectroscopic experiments indicates that hopping via NO₂YO– enhances Cuᴵ oxidation rates over single-step ET by factors of 32 (RuH107NO₂YO–109), 46 (RuH126NO₂YO–122), and 13 (RuH124NO₂YO–122).