title: Spectroscopic Investigations of Catalase Compound II: Characterization of an Iron(IV) Hydroxide Intermediate in a Non-thiolate-Ligated Heme Enzyme.
abstract: We report on the protonation state of Helicobacter pylori catalase compound II. UV/visible, Mössbauer, and X-ray absorption spectroscopies have been used to examine the intermediate from pH 5 to 14. We have determined that HPC-II exists in an iron(IV) hydroxide state up to pH 11. Above this pH, the iron(IV) hydroxide complex transitions to a new species (pKa= 13.1) with Mössbauer parameters that are indicative of an iron(IV)-oxo intermediate. Recently, we discussed a role for an elevated compound II pKain diminishing the compound I reduction potential. This has the effect of shifting the thermodynamic landscape toward the two-electron chemistry that is critical for catalase function. In catalase, a diminished potential would increase the selectivity for peroxide disproportionation over off-pathway one-electron chemistry, reducing the buildup of the inactive compound II state and reducing the need for energetically expensive electron donor molecules.
authors.affiliation: Departments of Chemistry & Molecular Biology and Biochemistry, University of California , Irvine, California 92697, United States.
authors.forename: Timothy H
authors.initials: TH
authors.lastname: Yosca
authors.affiliation: Department of Chemistry, Pennsylvania State University , University Park, Pennsylvania 16802, United States.
authors.forename: Matthew C
authors.initials: MC
authors.lastname: Langston
authors.affiliation: Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory , Menlo Park, California 94025, United States.
authors.forename: Courtney M
authors.initials: CM
authors.lastname: Krest
authors.affiliation: Department of Chemistry, Pennsylvania State University , University Park, Pennsylvania 16802, United States.
authors.forename: Elizabeth L
authors.initials: EL
authors.lastname: Onderko
authors.affiliation: Department of Chemistry, Pennsylvania State University , University Park, Pennsylvania 16802, United States.
authors.forename: Tyler L
authors.initials: TL
authors.lastname: Grove
authors.affiliation: Department of Chemistry, Pennsylvania State University , University Park, Pennsylvania 16802, United States.
authors.forename: Jovan
authors.initials: J
authors.lastname: Livada
authors.affiliation: Departments of Chemistry & Molecular Biology and Biochemistry, University of California , Irvine, California 92697, United States.
authors.forename: Michael T
authors.initials: MT
authors.lastname: Green
mesh_terms: D001665:Binding Sites; D002374:Catalase / Q000737:chemistry* / Q000378:metabolism; D016480:Helicobacter pylori / Q000201:enzymology*; D006863:Hydrogen-Ion Concentration; D006878:Hydroxides / Q000737:chemistry* / Q000378:metabolism; D058085:Iron Compounds / Q000737:chemistry* / Q000378:metabolism; D015394:Molecular Structure; D013056:Spectrophotometry, Ultraviolet; D015204:Spectroscopy, Mossbauer; D056928:X-Ray Absorption Spectroscopy
chemical_list: D006878:Hydroxides; D058085:Iron Compounds; D002374:Catalase