Sulfite Oxidase Activity of Cytochrome c: Role of Hydrogen Peroxide

Murugesan Velayutham; Craig F Hemann; Arturo J Cardounel; Jay L Zweier

doi:10.1016/j.bbrep.2015.11.025

Sulfite Oxidase Activity of Cytochrome c: Role of Hydrogen Peroxide

Biochem Biophys Rep. 2016 Mar 1:5:96-104. doi: 10.1016/j.bbrep.2015.11.025.

Authors

Murugesan Velayutham¹, Craig F Hemann², Arturo J Cardounel³, Jay L Zweier²

Affiliations

¹ Center for Biomedical EPR Spectroscopy and Imaging, Davis Heart and Lung Research Institute, and Division of Cardiovascular Medicine, Department of Internal Medicine, The Ohio State University College of Medicine, Columbus, Ohio 43210 ; Department of Cardiothoracic Surgery, University of Pittsburgh Medical Center, Pittsburgh, PA 15219.
² Center for Biomedical EPR Spectroscopy and Imaging, Davis Heart and Lung Research Institute, and Division of Cardiovascular Medicine, Department of Internal Medicine, The Ohio State University College of Medicine, Columbus, Ohio 43210.
³ Department of Cardiothoracic Surgery, University of Pittsburgh Medical Center, Pittsburgh, PA 15219.

Abstract

In humans, sulfite is generated endogenously by the metabolism of sulfur containing amino acids such as methionine and cysteine. Sulfite is also formed from exposure to sulfur dioxide, one of the major environmental pollutants. Sulfite is used as an antioxidant and preservative in dried fruits, vegetables, and beverages such as wine. Sulfite is also used as a stabilizer in many drugs. Sulfite toxicity has been associated with allergic reactions characterized by sulfite sensitivity, asthma, and anaphylactic shock. Sulfite is also toxic to neurons and cardiovascular cells. Recent studies suggest that the cytotoxicity of sulfite is mediated by free radicals; however, molecular mechanisms involved in sulfite toxicity are not fully understood. Cytochrome c (cyt c) is known to participate in mitochondrial respiration and has antioxidant and peroxidase activities. Studies were performed to understand the related mechanism of oxidation of sulfite and radical generation by ferric cytochrome c (Fe³⁺ cyt c) in the absence and presence of H₂O₂. Electron paramagnetic resonance (EPR) spin trapping studies using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) were performed with sulfite, Fe³⁺ cyt c, and H₂O₂. An EPR spectrum corresponding to the sulfite radical adducts of DMPO (DMPO-SO₃^-) was obtained. The amount of DMPO-SO₃^- formed from the oxidation of sulfite by the Fe³⁺ cyt c increased with sulfite concentration. In addition, the amount of DMPO-SO₃^- formed by the peroxidase activity of Fe³⁺ cyt c also increased with sulfite and H₂O₂ concentration. From these results, we propose a mechanism in which the Fe³⁺ cyt c and its peroxidase activity oxidizes sulfite to sulfite radical. Our results suggest that Fe³⁺ cyt c could have a novel role in the deleterious effects of sulfite in biological systems due to increased production of sulfite radical. It also shows that the increased production of sulfite radical may be responsible for neurotoxicity and some of the injuries which occur to humans born with molybdenum cofactor and sulfite oxidase deficiencies.

Keywords: Electron paramagnetic resonance (EPR); cytochrome c; mitochondria; peroxidase activity; spin trapping; sulfite radical.

Abstract

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