Resolving Complexity in the Interactions of Redox Enzymes and Their Inhibitors: Contrasting Mechanisms for the Inhibition of a Cytochrome c Nitrite Reductase Revealed by Protein Film Voltammetry
Cytochrome c nitrite reductase is a dimeric decaheme-containing enzyme that catalyzes the reduction of nitrite to ammonium. The contrasting effects of two inhibitors on the activity of this enzyme have been revealed, and defined, by protein film voltammetry (PFV). Azide inhibition is rapid and rever...
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Published in | Biochemistry (Easton) Vol. 43; no. 47; pp. 15086 - 15094 |
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Main Authors | , , |
Format | Journal Article |
Language | English |
Published |
United States
American Chemical Society
30.11.2004
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Subjects | |
Online Access | Get full text |
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Summary: | Cytochrome c nitrite reductase is a dimeric decaheme-containing enzyme that catalyzes the reduction of nitrite to ammonium. The contrasting effects of two inhibitors on the activity of this enzyme have been revealed, and defined, by protein film voltammetry (PFV). Azide inhibition is rapid and reversible. Variation of the catalytic current magnitude describes mixed inhibition in which azide binds to the Michaelis complex ( ∼ 40 mM) with a lower affinity than to the enzyme alone ( ∼ 15 mM) and leads to complete inhibition of enzyme activity. The position of the catalytic wave reports tighter binding of azide when the active site is oxidized ( ∼ 39 μM) than when it is reduced. By contrast, binding and release of cyanide are sluggish. The higher affinity of cyanide for reduced versus oxidized forms of nitrite reductase is immediately revealed, as is the presence of two sites for cyanide binding and inhibition of the enzyme. Formation of the monocyano complex by reduction of the enzyme followed by a “rapid” scan to high potentials captures the activity−potential profile of this enzyme form and shows it to be distinct from that of the uninhibited enzyme. The biscyano complex is inactive. These studies demonstrate the complexity that can be associated with inhibitor binding to redox enzymes and illustrate how PFV readily captures and deconvolves this complexity through its impact on the catalytic properties of the enzyme. |
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Bibliography: | istex:1605260BD0EF899581A1964CF32004ECADEBCB32 This work was funded by the EPSRC (DTA award to J.D.G.), the BBSRC through Grants 83/B17233, 6/P11528, and 83/B18695, and funding of the Centre for Metalloprotein Spectroscopy and Biology at University of East Anglia in addition to JIF Award 062178. ark:/67375/TPS-QDP9WVSP-Z ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 0006-2960 1520-4995 |
DOI: | 10.1021/bi049085x |