title: Formation of Hexacoordinate Mn(III) in Bacillus subtilis Oxalate Decarboxylase Requires Catalytic Turnover.
abstract: Oxalate decarboxylase (OxDC) catalyzes the disproportionation of oxalic acid monoanion into CO2 and formate. The enzyme has long been hypothesized to utilize dioxygen to form mononuclear Mn(III) or Mn(IV) in the catalytic site during turnover. Recombinant OxDC, however, contains only tightly bound Mn(II), and direct spectroscopic detection of the metal in higher oxidation states under optimal catalytic conditions (pH 4.2) has not yet been reported. Using parallel mode electron paramagnetic resonance spectroscopy, we now show that substantial amounts of Mn(III) are indeed formed in OxDC, but only in the presence of oxalate and dioxygen under acidic conditions. These observations provide the first direct support for proposals in which Mn(III) removes an electron from the substrate to yield a radical intermediate in which the barrier to C-C bond cleavage is significantly decreased. Thus, OxDC joins a small list of enzymes capable of stabilizing and controlling the reactivity of the powerful oxidizing species Mn(III).
authors.affiliation: Department of Chemistry & Chemical Biology, Indiana University Purdue University Indianapolis , Indianapolis, Indiana 46202, United States.
authors.forename: Wen
authors.initials: W
authors.lastname: Zhu
authors.affiliation: Department of Chemistry, University of California , Davis, California 95616, United States.
authors.forename: Jarett
authors.initials: J
authors.lastname: Wilcoxen
authors.affiliation: Department of Chemistry, University of California , Davis, California 95616, United States.
authors.forename: R David
authors.initials: RD
authors.lastname: Britt
authors.affiliation: Department of Chemistry & Chemical Biology, Indiana University Purdue University Indianapolis , Indianapolis, Indiana 46202, United States.
authors.forename: Nigel G J
authors.initials: NG
authors.lastname: Richards
mesh_terms: D001412:Bacillus subtilis / Q000201:enzymology*; D001426:Bacterial Proteins / Q000737:chemistry*; D055162:Biocatalysis; D002262:Carboxy-Lyases / Q000737:chemistry*; D056831:Coordination Complexes / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D006863:Hydrogen-Ion Concentration; D008345:Manganese / Q000737:chemistry*; D010070:Oxalates / Q000737:chemistry; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D011994:Recombinant Proteins / Q000737:chemistry
chemical_list: D001426:Bacterial Proteins; D056831:Coordination Complexes; D010070:Oxalates; D011994:Recombinant Proteins; D008345:Manganese; D002262:Carboxy-Lyases; C021915:oxalate decarboxylase; D010100:Oxygen