The autoxidation of pyrogallol was investigated in the presence of EDTA in the pH range 7.9–10.6.

The rate of autoxidation increases with increasing pH. At pH 7.9 the reaction is inhibited to 99% by superoxide dismutase, indicating an almost total dependence on the participation of the superoxide anion radical, O2·−, in the reaction. Up to pH 9.1 the reaction is still inhibited to over 90% by superoxide dismutase, but at higher alkalinity, O2·− -independent mechanisms rapidly become dominant.

Catalase has no effect on the autoxidation but decreases the oxygen consumption by half, showing that H2O2 is the stable product of oxygen and that H2O2 is not involved in the autoxidation mechanism.

A simple and rapid method for the assay of superoxide dismutase is described, based on the ability of the enzyme to inhibit the autoxidation of pyrogallol.

A plausible explanation is given for the non-competitive part of the inhibition of catechol O-methyltransferase brought about by pyrogallol.

https://febs.onlinelibrary.wiley.com/doi/epdf/10.1111/j.1432-1033.1974.tb03714.x

Involvement of the Superoxide Anion Radical in the Autoxidation of Pyrogallol and a Convenient Assay for Superoxide Dismutase

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1016/0014-5793%2874%2980281-4

Superoxide radicals as precursors of mitochondrial hydrogen peroxide

CHAPTER 6 – Oxygen Radicals, Hydrogen Peroxide, and Oxygen Toxicity

Reactions of H2O2 with superoxide dismutase were studied by e.p.r. (electron paramagnetic resonance) spectroscopy and other methods. In agreement with earlier work, the Cu2+ of the enzyme is reduced by H2O2, although the reaction does not go to completion and its kinetics are not simple. With dilute enzyme the time for half-reduction with 9mm-H2O2 is about 150ms. It is suggested that the reaction is a one-electron reduction, involving liberation of O2−. On somewhat more prolonged exposure to H2O2, the enzyme is inactivated. For enzyme in dilute solution and over a limited range of H2O2 concentrations, inactivation is first-order with respect to enzyme and reagent, with k=3.1m−1·s−1 at 20–25°C. Inactivation is accompanied by marked changes in the e.p.r. and visible spectra and appears to be associated with destruction of one histidine residue per subunit. It is suggested that this histidine is close to the metal in the native enzyme and essential for its enzymic activity.

/pdf/reduction-and-inactivation-of-superoxide-dismutase-by-1ku2u3obcp.pdf

E. Bunnenberg

Papers

A study on purified bovine erythrocuprein.