Application of Badger's rule to heme and non-heme iron-oxygen bonds: an examination of ferryl protonation states.
To gain insight into the protonation state of enzymatic ferryl species we have examined the applicability of Badger's rule to heme and non-heme iron-oxygen bonds. Using density functional theory we have calculated r(e) and nu(e) for the Fe-O bonds of complexes with different axial ligands, iron-oxidation, oxygen-protonation, and spin states. Our results indicate that Badger's rule holds for heme and non-heme oxo and hydroxo complexes. We find that the long Fe-O bonds that have been reported in the crystal structures of the ferryl forms of myoglobin, horseradish peroxidase, cytochrome c peroxidase, and catalase deviate substantially from the values predicted by Badger's rule, while the short Fe-O bonds obtained from X-ray absorption measurements are in good agreement with Badger's rule. In light of our analysis we conclude that the ferryl forms of myoglobin, horseradish peroxidase, and cytochrome c peroxidase are authentic iron(IV)oxos with Fe-O bonds on the order of 1.66 A and pKa's < 4.
Green
Michael T
MT
Department of Chemistry, The Pennsylvania State University, University Park, PA 16802, USA. mtg10@psu.edu
D002374:Catalase / Q000737:chemistry / Q000378:metabolism; D003578:Cytochrome-c Peroxidase / Q000737:chemistry* / Q000378:metabolism; D006418:Heme / Q000737:chemistry* / Q000378:metabolism; D006735:Horseradish Peroxidase / Q000737:chemistry* / Q000378:metabolism; D007501:Iron / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D009211:Myoglobin / Q000737:chemistry* / Q000378:metabolism; D010100:Oxygen / Q000737:chemistry* / Q000378:metabolism
D009211:Myoglobin; D006418:Heme; D007501:Iron; D006735:Horseradish Peroxidase; D003578:Cytochrome-c Peroxidase; D002374:Catalase; D010100:Oxygen