title: pH dependence of the active site of horseradish peroxidase compound II.
abstract: Using X-ray absorption spectroscopy, we investigated the active site of horseradish peroxidase (HRP) compound II at two different pH values. The results indicate that the bond length of the sixth coordinated ligand of the active site was 1.90 +/- 0.02 A at pH 7, decreasing to 1.72 +/- 0.02 A at pH 10. The average iron-to-pyrrole nitrogen and the proximal ligand bond lengths showed no significant changes. The position of higher coordination shells around the iron center changed, implying that some movement or deformation of nearby amino acid residues and/or of the heme occurred. Results of this study suggest that the decrease of the Fe-O bond length of HRP compound II at the higher pH might be attributed to the loss of a hydrogen bond which is present between the oxygen ligand and an amino acid residue in the heme pocket at pH 7.
authors.affiliation: National Center for the Design of Molecular Function, Utah State University, Logan 84322-4630.
authors.forename: C S
authors.initials: CS
authors.lastname: Chang
authors.forename: I
authors.initials: I
authors.lastname: Yamazaki
authors.forename: R
authors.initials: R
authors.lastname: Sinclair
authors.forename: S
authors.initials: S
authors.lastname: Khalid
authors.forename: L
authors.initials: L
authors.lastname: Powers
mesh_terms: D015502:Absorptiometry, Photon; D001665:Binding Sites; D006735:Horseradish Peroxidase / Q000737:chemistry / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry; D007527:Isoenzymes / Q000737:chemistry* / Q000378:metabolism; D008024:Ligands; D008958:Models, Molecular; D011487:Protein Conformation; D011758:Pyrroles / Q000737:chemistry
chemical_list: D007527:Isoenzymes; D008024:Ligands; D011758:Pyrroles; D007501:Iron; D006735:Horseradish Peroxidase