title: Redox Cycling, pH Dependence, and Ligand Effects of Mn(III) in Oxalate Decarboxylase from Bacillus subtilis.
abstract: This contribution describes electron paramagnetic resonance (EPR) experiments on Mn(III) in oxalate decarboxylase of Bacillus subtilis, an interesting enzyme that catalyzes the redox-neutral dissociation of oxalate into formate and carbon dioxide. Chemical redox cycling provides strong evidence that both Mn centers can be oxidized, although the N-terminal Mn(II) appears to have the lower reduction potential and is most likely the carrier of the +3 oxidation state under moderate oxidative conditions, in agreement with the general view that it represents the active site. Significantly, Mn(III) was observed in untreated OxDC in succinate and acetate buffers, while it could not be directly observed in citrate buffer. Quantitative analysis showed that up to 16% of the EPR-visible Mn is in the +3 oxidation state at low pH in the presence of succinate buffer. The fine structure and hyperfine structure parameters of Mn(III) are affected by small carboxylate ligands that can enter the active site and have been recorded for formate, acetate, and succinate. The results from a previous report [Zhu, W., et al. (2016) Biochemistry 55, 429-434] could therefore be reinterpreted as evidence of formate-bound Mn(III) after the enzyme is allowed to turn over oxalate. The pH dependence of the Mn(III) EPR signal compares very well with that of enzymatic activity, providing strong evidence that the catalytic reaction of oxalate decarboxylase is driven by Mn(III), which is generated in the presence of dioxygen.
authors: Department of Chemistry, University of Florida , Gainesville, Florida 32611-7200, United States.
authors: Umar T
authors: UT
authors: Twahir
authors: National High Magnetic Field Laboratory , 1800 East Paul Dirac Drive, Tallahassee, Florida 32310, United States.
authors: Andrew
authors: A
authors: Ozarowski
authors: Department of Chemistry, University of Florida , Gainesville, Florida 32611-7200, United States.
authors: Alexander
authors: A
authors: Angerhofer
mesh_terms: D001412:Bacillus subtilis / Q000201:enzymology*; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D001665:Binding Sites; D055162:Biocatalysis; D002245:Carbon Dioxide / Q000737:chemistry / Q000378:metabolism; D002262:Carboxy-Lyases / Q000737:chemistry / Q000378:metabolism*; D020134:Catalytic Domain; D004578:Electron Spin Resonance Spectroscopy; D005561:Formates / Q000737:chemistry / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008024:Ligands; D008345:Manganese / Q000737:chemistry / Q000378:metabolism*; D008956:Models, Chemical; D008958:Models, Molecular; D015394:Molecular Structure; D010070:Oxalates / Q000737:chemistry / Q000378:metabolism; D010084:Oxidation-Reduction
chemical_list: D001426:Bacterial Proteins; D005561:Formates; D008024:Ligands; D010070:Oxalates; C030544:formic acid; D002245:Carbon Dioxide; D008345:Manganese; D002262:Carboxy-Lyases; C021915:oxalate decarboxylase