Iron-containing SOD

SOD comprises a family of metalloproteins primarily classified into four groups copper, zinc-containing SOD (Cu, Zn-SOD), manganese-containing SOD (Mn-SOD), iron-containing SOD (Fe-SOD) and nickel-containing SOD (Ni-SOD). In the following studies, we will only focus on the uses of the former three kinds of SODs to construct SOD-based 02 biosensors since the last one, Ni-SOD, is not commercially available. 

CD spectroscopy has also been used to study the metal-binding and reactivity properties of iron- and manganese-containing SODs. These enzymes metabolize the superoxide ion radical O2 into molecular oxygen and hydrogen peroxide. The Fe- and Mn-SOD enzymes are strictly metal specific. Jackson and Brunold show that, despite the fact that Fe replacement of Mn in the Mn-SOD enzyme [(Mn Fe)-SOD] results in an inactive enzyme, the CD spectrum of wild-type Fe-SOD and (Mn - Fe)-SOD are remarkably similar. This suggests that the destroyed enzyme activity, upon replacement of the metal, does not occm via distortion of the enzyme active site. 

To diminish these threats, nature has created a family of metalloenzymes, the SODs. They catalyze the dismutation of superoxide to dioxygen and hydrogen peroxide (Eqs. (1) and (2)). They are differentiated by the redox-active metal copper (Cu/Zn SOD), manganese (MnSOD), iron (FeSOD), or nickel (NiSOD) superoxide dismutases and fall into three evolutionary families (Fig. 2) (10). The iron and manganese SODs are structurally similar and are found in prokaryotes and in the matrix of mitochondria (near the electron transport chain), respectively. Nickel containing SODs are known in some prokaryotes, whereas Cu/Zn are present in the cytosols of virtually all eukaryotic cells and have an independent evolutionary history. 

Iron SOD s are found in prokaryotes and plants Manganese and iron enzymes are phylogenetically older and they show great sequence homologies which are different from those of the Cu2Zn2superoxide dismutases Compared to the latter species, iron and manganese containing SOD s have received much less attention. 

Calcium ion enters the system not ordy in the form of water hardness but also in the form of calcium salts contained in the sod. Other heavy-metal ions such as aluminum and ferric iron may also be present in the sod, and must be removed by an appropriate budder to achieve good sod removal. Effective budders for cotton washing are those for which the calcium dissociation constant, expressed as or —logif -, is >4 and preferably >7 (33). 

The enzyme superoxide dismutase (SOD) occurs in three forms in mammalian systems (1) CuZnSOD (SOD1) found in the cytosol, (2) MnSOD (SOD2) found in mitochondria, and (3) CuZnSOD found in extracellular space (SOD3). Additionally, many bacterial SOD enzymes contain iron. SOD 1 has been discussed in detail... 

Bacterial SODs typically contain either nonheme iron (FeSODs) or manganese (MnSODs) at their active sites, although bacterial copper/zinc and nickel SODs are also known (Imlay and Imlay 1996 Chung et al. 1999). Catalases are usually heme-containing enzymes that catalyze disproportionation of hydrogen peroxide to water and molecular oxygen (Eq. 10.2) (Zamocky and Koller 1999 Loewen et al. 2000). 

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