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New insights of superoxide dismutase inhibition of pyrogallol autoxidation

Ramasarma, T and Rao, Aparna VS and Devi, MayaM and Omkumar, RV and Bhagyashree, KS and Bhat, SV (2015) New insights of superoxide dismutase inhibition of pyrogallol autoxidation. In: MOLECULAR AND CELLULAR BIOCHEMISTRY, 400 (1-2). pp. 277-285.

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Official URL: http://dx.doi.org/ 10.1007/s11010-014-2284-z


Autoxidation of pyrogallol in alkaline medium is characterized by increases in oxygen consumption, absorbance at 440 nm, and absorbance at 600 nm. The primary products are H2O2 by reduction of O-2 and pyrogallol-ortho-quinone by oxidation of pyrogallol. About 20 % of the consumed oxygen was used for ring opening leading to the bicyclic product, purpurogallin-quinone (PPQ). The absorbance peak at 440 nm representing the quinone end-products increased throughout at a constant rate. Prolonged incubation of pyrogallol in alkali yielded a product with ESR signal. In contrast the absorbance peak at 600 nm increased to a maximum and then declined after oxygen consumption ceased. This represents quinhydrone charge-transfer complexes as similar peak instantly appeared on mixing pyrogallol with benzoquinones, and these were ESR-silent. Superoxide dismutase inhibition of pyrogallol autoxidation spared the substrates, pyrogallol, and oxygen, indicating that an early step is the target. The SOD concentration-dependent extent of decrease in the autoxidation rate remained the same regardless of higher control rates at pyrogallol concentrations above 0.2 mM. This gave the clue that SOD is catalyzing a reaction that annuls the forward electron transfer step that produces superoxide and pyrogallol-semiquinone, both oxygen radicals. By dismutating these oxygen radicals, an action it is known for, SOD can reverse autoxidation, echoing the reported proposal of superoxide:semiquinone oxidoreductase activity for SOD. The following insights emerged out of these studies. The end-product of pyrogallol autoxidation is PPQ, and not purpurogallin. The quinone products instantly form quinhydrone complexes. These decompose into undefined humic acid-like complexes as late products after cessation of oxygen consumption. SOD catalyzes reversal of autoxidation manifesting as its inhibition. SOD saves catechols from autoxidation and extends their bioavailability.

Item Type: Journal Article
Publisher: SPRINGER
Additional Information: Copy right for this article belongs to the SPRINGER, VAN GODEWIJCKSTRAAT 30, 3311 GZ DORDRECHT, NETHERLANDS
Keywords: Pyrogallol autoxidation; Purpurogallin-quinone; Quinhydrone; Charge-transfer complex; SOD inhibition; Reverse autoxidation
Department/Centre: Division of Biological Sciences > Biochemistry
Date Deposited: 20 Feb 2015 12:07
Last Modified: 20 Feb 2015 12:07
URI: http://eprints.iisc.ac.in/id/eprint/50842

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