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Critical role of His369 in the reactivity of Pseudomonas aeruginosa cytochrome cd 1 nitrite reductase with oxygen
Author(s) -
Centola Fabio,
Rinaldo Serena,
Brunori Maurizio,
Cutruzzolà Francesca
Publication year - 2006
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/j.1742-4658.2006.05455.x
Subject(s) - nitrite reductase , heme , nitrite , chemistry , cytochrome , reductase , biochemistry , enzyme , nitric oxide , cytochrome p450 reductase , hemeprotein , stereochemistry , cytochrome c , coenzyme q – cytochrome c reductase , nitrate reductase , organic chemistry , nitrate , mitochondrion
In the denitrification pathway, Pseudomonas aeruginosa cytochrome cd 1 nitrite reductase catalyzes the reduction of nitrite to nitric oxide; in vitro , this enzyme is also competent in the reduction of O 2 to 2H 2 O. In this article, we present a comparative kinetic study of the O 2 reaction in the wild‐type nitrite reductase and in three site‐directed mutants (Tyr10→Phe, His369→Ala and His327→Ala/His369→Ala) of the amino acid residues close to the d 1 heme on the distal side. The results clearly indicate that His369 is the key residue in the control of reactivity, as its substitution with Ala, previously shown to affect the reduction of nitrite, also impairs the reaction with O 2 , affecting both the properties and lifespan of the intermediate species. Our findings allow the presentation of an overall picture for the reactivity of cytochrome cd 1 nitrite reductase and extend our previous conclusion that the conserved distal histidines are essential for the binding to reduced d 1 heme of different anions, whether a substrate such as nitrite, a ligand such as cyanide, or an intermediate in the O 2 reduction. Moreover, we propose that His369 also exerts a protective role against degradation of the d 1 heme, by preventing the formation and adverse effects of the reactive O 2 species (never present in significant amounts in wild‐type cytochrome cd 1 nitrite reductase), a finding with clear physiological implications.