Contrasting catalytic profiles of multiheme nitrite reductases containing CxxCK heme-binding motifs

Doyle, Rose-Marie, Marritt, Sophie J., Gwyer, James D., Lowe, Thomas G., Tikhonova, Tamara V., Popov, Vladimir O., Cheesman, Myles R. and Butt, Julea N. (2013) Contrasting catalytic profiles of multiheme nitrite reductases containing CxxCK heme-binding motifs. JBIC Journal of Biological Inorganic Chemistry, 18 (6). pp. 655-667. ISSN 0949-8257

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The multiheme cytochromes from Thioalkalivibrio nitratireducens (TvNiR) and Escherichia coli (EcNrfA) reduce nitrite to ammonium. Both enzymes contain His/His-ligated hemes to deliver electrons to their active sites, where a Lys-ligated heme has a distal pocket containing a catalytic triad of His, Tyr, and Arg residues. Protein-film electrochemistry reveals significant differences in the catalytic properties of these enzymes. TvNiR, but not EcNrfA, requires reductive activation. Spectroelectrochemistry implicates reduction of His/His-ligated heme(s) as being key to this process, which restricts the rate of hydroxide binding to the ferric form of the active-site heme. The K describing nitrite reduction by EcNrfA varies with pH in a sigmoidal manner that is consistent with its modulation by (de)protonation of a residue with p K ˜ 7.6. This residue is proposed to be the catalytic His in the distal pocket. By contrast, the K for nitrite reduction by TvNiR decreases approximately linearly with increase of pH such that different features of the mechanism define this parameter for TvNiR. In other regards the catalytic properties of TvNiR and EcNrfA are similar, namely, the pH dependence of V and the nitrite dependence of the catalytic current-potential profiles resolved by cyclic voltammetry, such that the determinants of these properties appear to be conserved.

Item Type: Article
Uncontrolled Keywords: magnetic circular dichroism,nitrogen cycle,cytochrome,modified tyrosine,reductive activation
Faculty \ School: Faculty of Science > School of Chemistry
Faculty of Science > School of Biological Sciences
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Depositing User: Pure Connector
Date Deposited: 30 Jul 2013 02:24
Last Modified: 09 Jul 2021 02:16
DOI: 10.1007/s00775-013-1011-7

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