Brief introduction to SODs

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

Electrochemical Sensors, Biosensors and Their Biomedical Applications 

Valentine et al. demonstrated that Cn + ions are in the same site in native Cn, Zn-SOD protein and CnESOD (E = empty, i.e. with removal of Zn ion from the native Cu, Zn-SOD) and the activity of the CnESOD is at least 80 5% that of the native Cu, Zn-SOD [99], However, the EZnSOD (E = empty, i.e. with removal of Cn ion from the native Cn, Zn-SOD) does not show any activity for catalytic dismntation of O2 . This snggests Cn + present in the Cn, Zn-SOD is essential for O2 dismntation even though Zn + is also required for dismutase activity [100-102]. 

The structures of the SODs (i.e. Cu, Zn-SOD, Ee-SOD, and Mn-SOD) in the SOD family are known to be relatively different. Eor instance, the Cu, Zn-SOD, which is the first SOD characterized and analyzed by X-ray methods [103], is a homodimer with a molecular weight of 31200 Da and containing one Cu (II) and Zn (11) per monomer subunit. Its fundamental structnral motif is a (3-barrel. In the Cu, Zn-SOD, the metals are bound by sequences connecting the barrel strands and are on opposite sides of the dimer with the Cu atoms separated by 33.8 A. The dimer is an elongated ellipsoid about 33 A wide, 67 A long and 36 A deep [103]. 

The second family of SODs, which utilizes either Fe or Mn to catalyze the dismutation of 02 (i.e. Fe-SOD and Mn-SOD), constitutes a close-knit group of proteins in which the sequences are highly conserved [104, 105]. Fe-SOD and Mn-SOD have been isolated as either dimers or tetramers [67]. Crystallographic analyses of both 

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