Dioxygen-activating iron center in putidamonooxin. Electron spin resonance investigation of the nitrosylated putidamonooxin.
The mononuclear non-haem iron center is the dioxygen-binding site of putidamonooxin which is the dioxygen-activating component of the 4-methoxybenzoate monooxygenase. Replacement of dioxygen by nitrosyl leads to the formation of a rather stable Fe3+ X NO- complex which is characterized by electron spin resonance (ESR) at g approximately equal to 4 and g approximately equal to 2. The ESR features can be composed by two spectral components which are characterized by different tetragonal distortions of the axial symmetry. Binding of 4-hydroxybenzoate, which is the product of the enzymatic reaction, leads to the formation of an ESR spectrum with pure axial symmetry. After binding of 4-methoxybenzoate, i.e. the physiological substrate of the monooxygenase, only one spectral component, i.e. that with a small tetragonal distortion, is observed. Binding of substrate analogues, like 4-aminobenzoate and 4-trifluoromethylbenzoate, leads to a spectral heterogeneity with variable amounts of the ESR component with a large tetragonal distortion. Benzoate induces an ESR spectrum with only that spectral component with large tetragonal distortion. The iron-depleted substrate-free form of the enzyme, ligated with NO, also shows ESR heterogeneity, i.e. both spectral components overlap, with 60% of the component with large tetragonal distortion. Binding of 4-methoxybenzoate leads to the occurrence of a pure spectrum, i.e. with small tetragonal distortion, whereas binding of benzoate leads to a pure spectrum with large tetragonal distortion. Thus, the structural heterogeneity is removed by binding of both the ligand (NO) and substrate. The Fe3+ X NO- complex is discussed as an analogue of the native oxy complex Fe3+ X O2-.
Twilfer
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Bernhardt
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Gersonde
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D001665:Binding Sites; D001711:Biotransformation; D055598:Chemical Phenomena; D002621:Chemistry; D002850:Chromatography, Gel; D004578:Electron Spin Resonance Spectroscopy; D007501:Iron / Q000032:analysis*; D008024:Ligands; D009589:Nitrogen Oxides / Q000378:metabolism*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism*; D010105:Oxygenases / Q000378:metabolism*; D011485:Protein Binding
D008024:Ligands; D009589:Nitrogen Oxides; D007501:Iron; D010105:Oxygenases; C022485:putidamonooxin; D010100:Oxygen