Bacteria manganese superoxide dismutase

In bacteria, on the other hand, the similar dimeric superoxide dismutase contains two Mn(II) ions per mole and no copper or zinc (55). In contrast, the enzyme from higher plants (eukaryotes) appears to be the Zn-Cu dimeric protein. The enzyme from green peas has been isolated as a Zn-Cu protein with molecular weight 31,500 (53) (Table I). Of great interest is the evidence that the manganese superoxide dismutase is present in chicken liver mitochondria (58). 

The importance of manganese for bacteria, such as that of Ni and to a lesser extent Co, as we saw in the last chapter, is considerable. Of course, as we will see shortly, it is also important in the tetranuclear Mn cluster that is involved in oxygen production in photosynthetic plants, algae and cyanobacteria, as well as in a number of mammalian enzymes such as arginase and mitochondrial superoxide dismutase. Most of manganese biochemistry can be explained on the one hand by its redox activity, and on the other by its analogy to Mg2+ (reviewed in Yocum and Pecoraro, 1999). 

Manganese plays a critical role in oxygen evolution catalyzed by the proteins of the photosynthetic reaction center. The superoxide dismutase of bacteria and mitochondria, as well as pyruvate carboxylase in mammals, are also manganese proteins. How the multiple manganese atoms of the photosynthetic reaction center participate in the removal of four electrons and protons from water is the subject of intense investigation by spectroscopists, synthetic inorganic chemists, and molecular biologists. ... 

Superoxide dismutase (SOD) is a widely distributed enzyme that exists in a variety of forms. The copper-zinc enzyme (Cu,ZnSOD) is primarily located in the cytosol of eukaryotic cells. Mitochondria contain, in the matrix space, a distinctive cyanide-insensitive manganese-containing enzyme (MnSOD) similar to that found in prokaryotes. In addition, a ferrienzyme (FeSOD) has been identified in bacteria that is also insensitive to cyanide. Amino acid sequence homologies indicate two families of superoxide dismutases. One of these is composed of the Cu,ZnSODs and the other of MnSODs and FeSODs. All these superoxide dismutases catalyze the same reaction (2H -H O2 -h OJ H2O2 -t- O2) and with comparable efficiency. 

Intracellular transport of metal ions has been a very well studied research area in the last few years. The most often-cited case of this transport involves copper transport in yeast by the copper metallochaperones 24, 25). Cu(I) enters the cytoplasm of yeast via copper transport receptors, and Cu(I) is bound by one of three transport proteins Lys7, Atxl, or Cox 17. Lys7 delivers copper to CuZn superoxide dismutase, Atxl delivers copper to ccc2 that activates an Fe(II) uptake system, and Cox 17 delivers copper to the mitochondria for the ultimate uptake into cytochrome c oxidase. A similar copper transport system has been reported in humans (26), and there may be a system in bacteria as well (27). Metal ion transport systems are known for iron, nickel, and manganese 24, 25, 28). However, no cytoplasmic Zn(II) transporters have been identified in... 

Superoxide dismutases of some microorganisms (such as Escherichia coli) and some animals contain Mn " /Mn + ions instead of copper and zinc ions as the cofactor (see Section 3.8.1.13.2). Catalases of some microorganisms (e.g. the bacteria Lactobacillus plantarum) contain manganese instead of haem iron. 

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