CuZn-Superoxide Dismutases in Rice: Occurrence of an Active, Monomeric Enzyme and Two Types of Isozyme in Leaf and Non-Photosynthetic Tissues

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Rice leaves and seed embryos contain four isozymes of CuZn-superoxide dismutase (SOD) and two isozymes of Mn-SOD. CuZn-SOD I is a major enzyme in leaves, but not in embryos or etiolated seedlings. CuZn-SODs II, III and IV were found in the embryos but were also found as minor isozymes in leaves. CuZn-SODs I, II and IV were purified to homogeneity from rice leaves. CuZn-SODs I and II had similar properties with respect to molecular weight, dimeric structure, absorption spectrum and metal content, but their amino acid compositions differed from each other. The absorption spectrum of CuZn-SOD IV was similar to that of isozymes I and II, but this enzyme was a monomer with a molecular mass of 1.7 kDa. Antibody against CuZn-SOD I from rice did not cross-react with isozymes II and IV. Antibodies against CuZn-SOD from spinach leaves cross-reacted with isozyme I but not with isozymes II, III and IV. By contrast, the antibodies against CuZn-SOD from spinach seeds cross-reacted with isozymes II, III and IV but not with isozyme I. Thus, the isozyme that is expressed mainly in leaves (CuZn-SOD I) and the isozymes expressed mainly in non-photosynthetic tissues (CuZn-SODs II, III, IV) are immunologically distinct.
日本植物生理学会の論文