Reaction of Carbon Monoxide with the Reduced Active Site of Bacterial Nitric Oxide Reductase

Bacterial nitric oxide reductase (NOR), a member of the superfamily of heme-copper oxidases, catalyzes the two-electron reduction of nitric oxide to nitrous oxide. The key feature that distinguishes NOR from the typical heme-copper oxidases is the elemental composition of the dinuclear center, which...

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Bibliographic Details
Published in:Biochemistry (Easton) 2001-11, Vol.40 (44), p.13361-13369
Main Authors: Hendriks, Janneke H. M, Prior, Louise, Baker, Adam R, Thomson, Andrew J, Saraste, Matti, Watmough, Nicholas J
Format: Article
Language:English
Subjects:
Binding Sites
Carbon Monoxide - metabolism
Cell Division
Circular Dichroism
Copper - metabolism
Electron Spin Resonance Spectroscopy
Electron Transport
Electrons
Heme - chemistry
Heme - metabolism
Iron - chemistry
Iron - metabolism
Kinetics
Ligands
Oxidation-Reduction
Oxidoreductases - metabolism
Paracoccus denitrificans - enzymology
Photolysis
Spectrophotometry
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Summary:Bacterial nitric oxide reductase (NOR), a member of the superfamily of heme-copper oxidases, catalyzes the two-electron reduction of nitric oxide to nitrous oxide. The key feature that distinguishes NOR from the typical heme-copper oxidases is the elemental composition of the dinuclear center, which contains non-heme iron (FeB) rather than copper (CuB). UV−vis electronic absorption and room-temperature magnetic circular dichroism (RT-MCD) spectroscopies showed that CO binds to Fe(II) heme b 3 to yield a low-spin six-coordinate species. Photolysis of the Fe(II)-CO bond is followed by CO recombination (k on = 1.7 × 108 M-1 s-1) that is approximately 3 orders of magnitude faster than CO recombination to the active site of typical heme-copper oxidases (k on = 7 × 104 M-1 s-1). This rapid rate of CO recombination suggests an unimpeded pathway to the active site that may account for the enzyme's high affinity for substrate, essential for maintaining denitrification at low concentrations of NO. In contrast, the initial binding of CO to reduced heme b 3 measured by stopped-flow spectroscopy is much slower (k on = 1.2 × 105 M-1 s-1). This suggests that an existing heme distal ligand (water/OH-) may be displaced to elicit the spin-state change observed in the RT-MCD spectrum.
ISSN:0006-2960
1520-4995
DOI:10.1021/bi011428t