Electron Flow through Nitrotyrosinate in Pseudomonas aeruginosa Azurin.

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). [ABSTRACT FROM AUTHOR]