EPR characterisation of the ferrous nitrosyl complex formed within the oxygenase domain of NO synthase

Chembiochem. 2013 Sep 23;14(14):1852-7. doi: 10.1002/cbic.201300233. Epub 2013 Aug 13.


Nitric oxide is produced in mammals by a class of enzymes called NO synthases (NOSs). It plays a central role in cellular signalling but also has deleterious effects, as it leads to the production of reactive oxygen and nitrogen species. NO forms a relatively stable adduct with ferrous haem proteins, which, in the case of NOS, is also a key catalytic intermediate. Despite extensive studies on the ferrous nitrosyl complex of other haem proteins (in particular myoglobin), little characterisation has been performed in the case of NOS. We report here a temperature-dependent EPR study of the ferrous nitrosyl complex of the inducible mammalian NOS and the bacterial NOS-like protein from Bacillus subtilis. The results show that the overall behaviours are similar to those observed for other haem proteins, but with distinct ratios between axial and rhombic forms in the case of the two NOS proteins. The distal environment appears to control the existence of the axial form and the evolution of the rhombic form.

Keywords: EPR spectroscopy; NO-synthases; heme proteins; nitrosyl complexes.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacillus subtilis / enzymology
  • Coordination Complexes / chemistry*
  • Electron Spin Resonance Spectroscopy*
  • Ferrous Compounds / chemistry*
  • Isoenzymes / chemistry
  • Isoenzymes / metabolism
  • Myoglobin / chemistry
  • Myoglobin / metabolism
  • Nitric Oxide / chemistry*
  • Nitric Oxide / metabolism
  • Nitric Oxide Synthase Type II / chemistry*
  • Nitric Oxide Synthase Type II / genetics
  • Nitric Oxide Synthase Type II / metabolism
  • Protein Structure, Tertiary
  • Recombinant Proteins / biosynthesis
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / genetics
  • Substrate Specificity
  • Temperature


  • Coordination Complexes
  • Ferrous Compounds
  • Isoenzymes
  • Myoglobin
  • Recombinant Proteins
  • Nitric Oxide
  • Nitric Oxide Synthase Type II