Properties of Superoxide Radical and Analytical Methods

Streptococcus mutants9) are exceptions in that they can be reactivated from the respective apoenzymes by either Mn or Fe ions. 

The Mn ion in B. stearothermophilus Mn—SOD is ligated by His-26, His-81, Asp-163, and His-167, with a tetrahedral arrangement strongly distorted toward trigonal pyramidal. Tyr-34, whose hydroxy group is only 5 A apart from the metal, is involved in the catalytic reaction, and the Mn-site is particularly rich in aromatic amino acid residues (Fig. 10.8). 

The substrate of SOD, Oi, has unique properties as a reactive and unstable radical, as compared to stable substrates for most enzymes. O2 is spontaneously disproportionated at an appreciable rate, and its life time is only 5 s when produced at 1 pM s at pH 7. SOD catalyzes the disproportionation of O2 at a diffusion-controlled rate, and to study such a 

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