Ultrafast ligand binding dynamics in the active site of native bacterial nitric oxide reductase

• Published in: Biochimica et biophysica acta 2008-07, Vol.1777 (7-8), p.919-924
• Main Authors: Kapetanaki, Sofia M., Field, Sarah J., Hughes, Ross J.L., Watmough, Nicholas J., Liebl, Ursula, Vos, Marten H.
• Format: Article
• Language: English
• Subjects: Bacterial Proteins - chemistry; Bacterial Proteins - metabolism; Binding Sites; Carbon Monoxide - metabolism; Dinuclear center; Electron Spin Resonance Spectroscopy; Heme; Ligand dynamics; Ligands; Nitric Oxide - metabolism; Nitric oxide reductase; Oxidation-Reduction; Oxidoreductases - chemistry; Oxidoreductases - metabolism; Paracoccus denitrificans - enzymology; Protein Binding; Spectrophotometry; Ultrafast spectroscopy
• ISSN: 0005-2728; 0006-3002; 1879-2650
• DOI: 10.1016/j.bbabio.2008.03.012

The active site of nitric oxide reductase from Paracoccus denitrificans contains heme and non-heme iron and is evolutionarily related to heme-copper oxidases. The CO and NO dynamics in the active site were investigated using ultrafast transient absorption spectroscopy. We find that, upon photodissociation from the active site heme, 20% of the CO rebinds in 170 ps, suggesting that not all the CO transiently binds to the non-heme iron. The remaining 80% does not rebind within 4 ns and likely migrates out of the active site without transient binding to the non-heme iron. Rebinding of NO to ferrous heme takes place in ~13 ps. Our results reveal that heme-ligand recombination in this enzyme is considerably faster than in heme-copper oxidases and are consistent with a more confined configuration of the active site.