Catalases in Plants - Catalases in Plants: Gene Structure,...

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Catalases in Plants: Gene Structure, Properties, Regulation, and Expression John G. Scandalios, Lingqiang Guan, and Alexios N. Polidoros Department of Genetics North Carolina State University Raleigh, North Carolina 27695-7614 Catalase action in plant and animal tissues was first observed in 1818 by Thenard, who noted that such tissues readily degraded hydrogen peroxide, a substance he had also discovered some years earlier (Aebi and Sutter 1971). Loew (1901) first established that the degradation of H 2 0 2 in tissues was due to the effect of an individual, separable enzyme, which he named "catalase." Warburg (1923) suggested that catalase is an iron-containing enzyme, because it is inhibited by cyanide. Evidence for its hematin prosthetic group was presented by Zeile and Hellstrom (1930). Catalase was first purified and crystallized from beef liver, and its identity was made clear by Sumner and Dounce (1937). The earliest genetic studies on catalase were reported by the Russian biologist Kolt- zoff (1927), who demonstrated that blood catalase levels in several animal species are inherited and segregate according to Mendelian rules. Catalase has been found in all plants examined, and has been most thoroughly studied biochemically, genetically, and molecularly in the agronomically important species Zea mays L. (Scandalios 1990). That catalases can exist in multiple molecular forms or isozymes encoded by multiple genes, in any organism, was first demonstrated by Scandalios (1965, 1968) with the maize catalases and has since been found to be the rule rather than the exception, as originally perceived. OXYGEN AND REACTIVE OXYGEN SPECIES During respiration, molecular oxygen accepts four electrons to produce two molecules of H 2 0. However, because of spin restrictions, 0 2 cannot accept four electrons at once but accepts them one at a time (Halliwell and Outteridge 1984). Thus, during the one-electron (univalent) reduction of 0 2 , stable intermediates are formed in a stepwise fashion (Fig.1). Oxidative Stress and the Molecular Biology of Antioxidant Defenses © 1997 Cold Spring Harbor Liboratory Press 0-87969-502-1/97 $5 + .00 343
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344 J.G. Scandalios, L. Guan, and A.N. Polidoros Figure 1 Pathways in the univalent reduction of oxygen to water leading to the formation of various intermediate reactive oxygen species. Each of the intermediate reactive oxygen species (ROS) can react with a variety of biomolecules, altering or blocking their biological activity. The combined biological effect of these toxic oxygen species on organisms is termed "oxidative stress." To minimize the damaging effects of activated oxygen, organisms have evolved various enzymatic and nonenzymatic mechanisms that can reduce oxidative stress by detoxifying harmful oxygen species. Among these defenses is the antioxidant enzyme catalase, which converts H 2 0 2 to oxygen and water. Unlike the oxygen radicals, H
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This note was uploaded on 09/13/2010 for the course DGPB 024e taught by Professor Alexiospolidoros during the Spring '10 term at Aristotle University of Thessaloniki.

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Catalases in Plants - Catalases in Plants: Gene Structure,...

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