bi6b00891_si_001.pdf (2.61 MB)
Redox Cycling, pH Dependence, and Ligand Effects of Mn(III) in Oxalate Decarboxylase from Bacillus subtilis
journal contribution
posted on 2016-10-31, 00:00 authored by Umar T. Twahir, Andrew Ozarowski, Alexander AngerhoferThis
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.