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Electron Distribution within the Cytochrome c Nitrite Reductase Hemes as a Function of Applied Potential: a Spectro‐Potentiometric Analysis
Author(s) -
Stein Natalia,
Bennett Brian,
Pacheco Andy
Publication year - 2013
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.27.1_supplement.lb63
Subject(s) - chemistry , heme , cyanide , nitrite reductase , potentiometric titration , electron transfer , titration , active site , electron paramagnetic resonance , cytochrome , nitrite , electron transport chain , photochemistry , inorganic chemistry , stereochemistry , nuclear magnetic resonance , enzyme , biochemistry , electrode , organic chemistry , physics , nitrate
Cytochrome c Nitrite Reductase (CcNiR) is a dimeric multi‐heme enzyme that catalyzes the reduction of nitrite to ammonia. The ten heme moieties within the dimer are arranged in such proximity to each other as to form a wire that is used to transfer electrons from a physiological donor to substrate bound at the unique active site. This poster will present two results from recent studies: the effect of added cyanide on the ccNiR heme midpoint potentials, and the binding affinity of the oxidized ccNiR active site for nitrite and cyanide. These studies form part of a larger mechanistic study of the enzyme. UV/Vis spectropotentiometric titrations of ccNiR in the presence and absence of cyanide reveal 5 distinct Nernstian potentials that can be modeled as 1‐electron reduction steps. When cyanide is bound to the active site the midpoint potential of the highest‐potential heme shifts nearly 70 mV in the positive direction, while the potentials of the next two hemes each shift by about 25 mV in the same direction. The two lowest‐potential hemes are unaffected by cyanide. Spectral analysis suggests that in all cases individual electrons are distributed among several hemes, rather than being localized on a single heme. The spectropotentiometric titrations are now being repeated using electron paramagnetic resonance (EPR) spectroscopy in place of UV/Vis, in order to obtain detailed information about individual hemes.