title: Histidine-tailed microperoxidase-10: a pH-dependent ligand switch.
abstract: The electronic absorption and magnetic circular dichroism (MCD) spectra of ferric histidine-tailed microperoxidase-10 (His-MP10) change dramatically as the pH is raised from 1.8 to 11.8. Two distinct species are observed (pKa = 4.4). The spectra of acidic ferric His-MP10 nearly match those of ferric mesoporphyrin-reconstituted myoglobin and so the axial ligands are assigned to be histidine and water. The retention of histidine ligation below pH 4 contrasts to the behavior of myoglobin and horseradish peroxidase which convert to five-coordinate water ligated and then lose the heme prosthetic group at even lower pH. Neutral and alkaline ferric His-MP10 have spectra that are very similar to those of the imidazole complex of ferric mesoporphyrin-reconstituted myoglobin. Thus, we conclude that it is bis-histidine ligated with the C-terminal histidine bound as the sixth ligand. Thus, ferric His-MP10 exhibits a pH-dependent ligand switch with a change in axial ligation from water and histidine at low pH to bis-histidine at neutral and alkaline pH.
authors.affiliation: Department of Chemistry and Biochemistry, University of South Carolina, Columbia 29208, USA.
authors.forename: J
authors.initials: J
authors.lastname: Cheek
authors.forename: D W
authors.initials: DW
authors.lastname: Low
authors.forename: H B
authors.initials: HB
authors.lastname: Gray
authors.forename: J H
authors.initials: JH
authors.lastname: Dawson
mesh_terms: D002942:Circular Dichroism; D004579:Electron Transport; D006420:Hemeproteins / Q000737:chemistry / Q000378:metabolism; D006639:Histidine / Q000737:chemistry* / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008024:Ligands; D008786:Metmyoglobin / Q000737:chemistry / Q000378:metabolism; D010544:Peroxidases / Q000737:chemistry* / Q000378:metabolism
chemical_list: D006420:Hemeproteins; D008024:Ligands; D008786:Metmyoglobin; D006639:Histidine; D010544:Peroxidases; C021799:microperoxidase