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Biological Chemistry

Editor-in-Chief: Brüne, Bernhard

Editorial Board Member: Buchner, Johannes / Ludwig, Stephan / Sies, Helmut / Turk, Boris / Wittinghofer, Alfred

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Irreversible Thiol Oxidation in Carbonic Anhydrase III: Protection by S-Glutathiolation and Detection in Aging Rats

R.J. Mallis / M.J. Hamann / W. Zhao / T. Zhang / S. Hendrich / J.A. Thomas

Citation Information: Biological Chemistry. Volume 383, Issue 3-4, Pages 649–662, ISSN (Print) 1431-6730, DOI: 10.1515/BC.2002.067, June 2005

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Proteins with reactive sulfhydryls are central to many important metabolic reactions and also contribute to a variety of signal transduction systems. In this report, we examine the mechanisms of oxidative damage to the two reactive sulfhydryls of carbonic anhydrase III. Hydrogen peroxide (H2O2), peroxy radicals, or hypochlorous acid (HOCl) produced irreversibly oxidized forms, primarily cysteine sulfinic acid or cysteic acid, of carbonic anhydrase III if glutathione (GSH) was not present. When GSH was approximately equimolar to protein thiols, irreversible oxidation was prevented. H2O2 and peroxyl radicals both generated Sglutathiolated carbonic anhydrase III via partially oxidized protein sulfhydryl intermediates, while HOCl did not cause Sglutathiolation. Thus, oxidative damage from H2O2 or AAPH was prevented by protein Sglutathiolation, while a direct reaction between GSH and oxidant likely prevents HOClmediated protein damage. In cultured rat hepatocytes, carbonic anhydrase III was rapidly Sglutathiolated by menadione. When hepatocyte glutathione was depleted, menadione instead caused irreversible oxidation. We hypothesized that normal depletion of glutathione in aged animals might also lead to an increase in irreversible oxidation. Indeed, both total protein extracts and carbonic anhydrase III contained significantly more cysteine sulfinic acid in older rats compared to young animals. These experiments show that, in the absence of sufficient GSH, oxidation reactions lead to irreversible protein sulfhydryl damage in purified proteins, cellular systems, and whole animals.

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