Chloroplastic SODs

The cytosolic (SOD-1) and chloroplastic (SOD-3) isozymes were determined of their NH2 terminal up to 24 residues (Fig. 4). It is obvious that both SOD-1 and SOD-3 are evolutionally related to the compared SOD s from other plant sources. Position 4, 5, 6,7, 8, 9, 15, and 17 are highly conserved compared to SODs from spinach and pea chloroplasts (4,5) and from maize cytosol (6). In addition SOD-1 are conserved in position 21 of the cytosolic enzyme compared to the other plants. The percentage homology of the NH2-teminal sequence (residue 1-23) between pine and spinach and pea stromal enzyme was high, 83% and 87% respectively. However the percentage homology of the NH2 -teminal sequence (residue 2-23) between pine and maize cytosolic SOD s was lower (41 %). 

IV. Superoxide dismutase (EC 1.15.1.1) Within a cell the superoxide dismutases (SODs) constitute the first line of defense against ROS. Superoxide radical (02) is produced where an electron transport chain is present, as in mitochondria and chloroplasts, but 02 activation may occur in other subcellular locations such as glyoxysomes, peroxisomes, apoplast and the cytosol. Thus SODs are present in all these cellular locations, converting superoxide into hydrogen peroxide and water (i.e. copper/zinc SODs are typically found in the nuclei and cytosol of eukaryotic cells). 

Four distinct forms of SODs are found in nature, which fall into three families. The Cu/Zn SODs occur primarily in cytoplasm of eukaryotes and chloroplasts, hut have also heen found in a few species of bacteria, nickel-containing SODs are known in some prokaryotes, while the structurally related Mn- and FeSODs are found in... 

Finally superoxide radicals can also be generated photochemically in chloroplasts in the presence of ascorbate or of paraquat. The formation was demonstrated by spin trapping on illumination of spinach chloroplasts in the presence of oxygen and paraquat Superoxide radicals are formed, moreover, in the near-ultraviolet photooxidation of tryptophan, as indicated by the increase of the HjO production in the presence of SOD and on irradiation in aerated solutions of protoporphyrin at 400 nm and of melanin with light of 320—600nmas shown by spintrapping. 

The (Cu,Zn)-SOD is found in the cytosol of eukaryotic cells and in the intermembrane space of mitochondria, as observed with chicken liver and also in chloroplasts, as shown with spinach and mustard leaves. A (Cu,Zn)-SOD has also been isolated from a prokaryote Photobacterium leiognathi. Could this symbiotic bacterium have borrowed the gene(s) from its host, the Pony fish, although two different subunits (Af 15,000 and 17,000) were reported for the bacterial enzyme A (Cu,Zn)-SOD was furthermore detected in Paracoccus denitrificans... 

Surprisingly, too, there are claims of higher oxidation states of Mn in some systems, e.g. Mnlv in photosynthetic(II) chloroplast systems and Mn111 in acid phosphatase. In the latter enzyme Tyr and Cys residues appear to form part of the metal-binding site. The metal is also involved in the phosphate binding. While superoxide dismutase (SOD) is more generally found with Cu and Zn as the active metals, an Mn-SOD form is found in certain bacteria. The Mn oscillates between different oxidation states in its catalytic activity.149... 

Chloroplast type of CuZn-SOD isozyme is localized in the chloroplast stroma of most plants, whereas Fe-SOD occurs in chloroplasts of Euglena, the moss Marchantia polymorpha and several species of seed plant. So far Mn-SOD has not been detected in chloroplasts in a soluble form but occurs in a thylakoid membrane-bound form.23,24) The cytosolic CuZn-SOD, which is distinguishable from the chloroplastic CuZn-SOD in terms of amino acid sequence, occurs in cell compartments other than chloroplasts and in nonphotosynthetic tissues.14)... 

Fig. 10.3 Amino acid sequences of CuZn-SODs from various organisms.31 Yeast, Saccharomyces cerevisiae Neurospora, Neurospora crassa Arabido., Arabidopsis thaliana Cyt, cytosolic CuZn-SOD Chi, chloroplastic CuZn-SOD. Amino acid residue number is based on that of human CuZn-SOD. Residues conserved in all species are boxed.

Higher plant chloroplasts contain a cyanide-insensitive, membrane-bound SOD which may also occur in blue-green algae (39—41, 47, 48, 59). This is rather a complicated system, but we think that the mem-... 

Cu,Zn-containing SODs (Cu,Zn-SODs) are known as the cytosolic and extracellular SODs of animals however, they are also found in plants, animals, fungi and bacteria, and are encoded in several viral genomes.In animals, Cu,Zn-SOD is also found in the nucleus, the mitochondrial intermembrane space, and lysosomes. In plants, distinct Cu,Zn-SODs are found in the chloroplast and cytoplasm. The prokaryotic Cu,Zn-SODs as a group are distinct from the eukaryotic Cu,Zn-SODs. Recent reviews of Cu,Zn-SOD include those of Bordo and Bertini. ... 

Figure 7. Nitrite formation from hydroxylamine. Reaction mixture contained in 3 mL 50 mM phosphate buffer pH 7.8 1 fjjnol of NH OH chloroplasts with 75 /xg of chlorophyll and where indicated 6.6 /aM paraquat 50 units SOD. Illuminated at 275 Wm at 22°C. Key control, plus paraquat. A plus SOD, and plus paraquat and SOD, A (72).

Enzyme assays Intact chloroplasts were isolated and then osmotic-ally shocked. The lysates were used for determination of the stromal activities of ascorbate peroxidase (6), monodehydroascorbate reductase (7) and dehydroascorbate reductase (6). Superoxide dismutase (SOD) was assayed (8) in a protein extract derived from chloroplasts solubilized in the presence of 2.5% Triton-X-100. Catalase activity was determined (9) in leaf homogenates. 

Data are relative to the sensitive biotype. SOD — the chloroplast isozyme of a Cu-Zn superoxide dismutase, GR-glutathione reductase, AP-ascorbate peroxidase. 

Martin JP, Haider K, Wolf D (1972) Synthesis of phenolic polymers by Hedersormla toruloidea in relation to humic add formation. Sod Sd Soc Am Proc 36 311-315 Moreland DE, Novitzky WP (1987) Effects of phenolic adds, coumaiins, emd flavonoids on isolated chloroplasts and mitochondria. In Wader GR (ed) AUelochemiceils role in agriculture and forestry. ACS symposium series, vol 330. American Chemical Sodety, Washington, DC, pp 247-261... 

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