Alexander Angerhofer

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Name: Angerhofer, Alexander

Organization: University of Florida , USA

Department: Department of Chemistry

Title: Professor(PhD)

Chemicals
References

Redox Cycling, pH Dependence, and Ligand Effects of Mn(III) in Oxalate Decarboxylase from Bacillus subtilis

Co-reporter:Umar T. Twahir, Andrew Ozarowski, and Alexander Angerhofer

Biochemistry 2016 Volume 55(Issue 47) pp:

Publication Date(Web):October 31, 2016

DOI:10.1021/acs.biochem.6b00891

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.

Atomic hydrogen as high-precision field standard for high-field EPR

Co-reporter:Stefan Stoll, Andrew Ozarowski, R. David Britt, Alexander Angerhofer

Journal of Magnetic Resonance 2010 Volume 207(Issue 1) pp:158-163

Publication Date(Web):November 2010

DOI:10.1016/j.jmr.2010.08.006

We introduce atomic hydrogen trapped in an octaisobutylsilsesquioxane nanocage (H@iBuT8) as a new molecular high-precision magnetic field standard for high-field EPR spectroscopy of organic radicals and other systems with signals around g = 2. Its solid-state EPR spectrum consists of two 0.2 mT wide lines separated by about 51 mT and centered at g ≈ 2. The isotropic g factor is 2.00294(3) and essentially temperature independent. The isotropic 1H hyperfine coupling constant is 1416.8(2) MHz below 70 K and decreases slightly with increasing temperature to 1413.7(1) MHz at room temperature. The spectrum of the standard does not overlap with those of most organic radicals, and it can be easily prepared and is stable at room temperature.

Synthesis of Water-Soluble 2,2′-Diphenyl-1-Picrylhydrazyl Nanoparticles: A New Standard for Electron Paramagnetic Resonance Spectroscopy

Co-reporter:Ou Chen ; Jiaqi Zhuang ; Fabrizio Guzzetta ; Jared Lynch ; Alexander Angerhofer ;Y. Charles Cao

Journal of the American Chemical Society 2009 Volume 131(Issue 35) pp:12542-12543

Publication Date(Web):August 12, 2009

DOI:10.1021/ja905395u

This communication reports a size-controlled synthesis of water-soluble 2,2′-diphenyl-1-picrylhydrazyl (DPPH) nanoparticles (NPs). These nanoparticles exhibit size-dependent absorption spectra and fast spin exchange-narrowed single-line EPR spectra. The linewidths of the EPR spectra of these water-soluble nanoparticles are ∼1.5−1.8 G, which are equal or close to the narrowest line width (1.5 G) of the common DPPH standard in the form of water-insoluble microcrystals. In addition, these NPs are stable over a wide pH range of 3.0 to 10.0. These properties make these water-soluble DPPH NPs suitable for use as a new type of EPR standard, which is important for fundamental research and practical applications in fields such as the food industry and the life sciences. Furthermore, the DPPH NPs can potentially be used as a spin probe in biomedical studies.

EPR at 24 T of the primary donor radical cation from Blastochloris viridis

Co-reporter:Peter J. Bratt, Peter Heathcote, Alia Hassan, Johann van Tol, Louis-Claude Brunel, Joshua Schrier, Alexander Angerhofer

Chemical Physics 2003 Volume 294(Issue 3) pp:277-284

Publication Date(Web):1 November 2003

DOI:10.1016/S0301-0104(03)00281-7

Abstract

The g-matrix of photosynthetic pigments has been studied in the last decade due to the advent of high-field EPR techniques. It can be observed when the spectral splitting of the principal g-factor components is larger than the linewidth due to unresolved hyperfine splitting and if there is no g-strain obscuring it. For large organic molecules such as the primary electron donor in photosynthetic reaction centers (RC) this usually requires fields above 11 T, or, for fields between 3 and 11 T, full deuteration and/or single crystal work. Here we present for the first time the fully resolved rhombic EPR spectrum of the primary donor of Blastochloris viridis (formerly called Rhodopseudomonas viridis), a purple photosynthetic bacterium containing bacteriochlorophyll b. As was the case for Rhodobacter sphaeroides, g-strain is negligible for this radical up to a field of 24 T. The temperature dependence of the g-anisotropy is presented and compared with that of the bacteriochlorophyll a-containing Rb. sphaeroides and plant photosystem I. A slight shift in the principal components of the g-matrix is observed at temperatures below 70 K, where it becomes more axial. The experimental work is complemented with theoretical calculations for g using the semi-empirical INDO/S method as implemented in the program ZINDO. The theoretical results generally agree well with the experiment. This indicates that a satisfactory description of the anisotropic g-tensor for radical cations of large planar molecules like the chlorophylls as well as their aggregates, e.g., reaction center primary donor special pairs, is possible with this relatively cheap semi-empirical approach.

Immobilization of Bacillus subtilis oxalate decarboxylase on a Zn-IMAC resin

Co-reporter:Umar Twahir, Laura Molina, Andrew Ozarowski, Alexander Angerhofer

Biochemistry and Biophysics Reports (December 2015) Volume 4() pp:98-103

Publication Date(Web):December 2015

DOI:10.1016/j.bbrep.2015.08.017

EPR spin trapping of an oxalate-derived free radical in the oxalate decarboxylase reaction

Co-reporter:Witcha Imaram, Benjamin T. Saylor, Christopher P. Centonze, Nigel G.J. Richards, Alexander Angerhofer

Free Radical Biology and Medicine (15 April 2011) Volume 50(Issue 8) pp:1009-1015

Publication Date(Web):15 April 2011

DOI:10.1016/j.freeradbiomed.2011.01.023

EPR spin trapping experiments on bacterial oxalate decarboxylase from Bacillus subtilis under turn-over conditions are described. The use of doubly 13C-labeled oxalate leads to a characteristic splitting of the observed radical adducts using the spin trap N-tert-butyl-α-phenylnitrone linking them directly to the substrate. The radical was identified as the carbon dioxide radical anion which is a key intermediate in the hypothetical reaction mechanism of both decarboxylase and oxidase activities. X-ray crystallography had identified a flexible loop, SENS161-4, which acts as a lid to the putative active site. Site directed mutagenesis of the hinge amino acids, S161 and T165 was explored and showed increased radical trapping yields compared to the wild type. In particular, T165V shows approximately ten times higher radical yields while at the same time its decarboxylase activity was reduced by about a factor of ten. This mutant lacks a critical H-bond between T165 and R92 resulting in compromised control over its radical chemistry allowing the radical intermediate to leak into the surrounding solution.