Microbial superoxide dismutases

One last class of mononuclear non-haem iron enzyme that we have not yet considered, consists of the microbial superoxide dismutases with Fe(III) at their active site. The crystal structure of the E. coli enzyme shows a coordination geometry reminiscent of protocatechuate 3,4-dioxygenase, with four endogenous protein ligands, three His and one Asp residue, and one bound water molecule (Carlioz et ah, 1988). 

This reaction is also catalyzed by superoxide dismutase (SOD), which occurs in milk at very low concentrations (Fox and Morrissey, 1981). Hydrogen peroxide can also be formed in milk as a result of microbial metabolism or by reduction of superoxide by ascorbic acid. A mean level of 0.02 mg/1 hydrogen peroxide has been reported in milk (Toyoda et al, 1982). 

The major role of manganese in biology is in oxygen production by photosynthetic plants, algae, and cyanobacteria. It is also involved in a number of mammalian enzymes like arginase and mitochondrial superoxide dismutase and it also plays an important role in microbial metabolism. Most of manganese biochemistry can be... 

The stability of the enzymes is usually greatly enhanced within the protecting environment of the microbial cell because here also enzymes (e.g., catalase and superoxide dismutase) for the detoxification of reactive oxygen species, which might be formed by the CYPs, are present. 

Iron-containing superoxide dismutases have been isolated from a variety of microbial sources (Yost and Fridovich, 1973 Asada et al, 1975 Lumsden and Hall, 1974 Puget and Michelson, 1974a,b Yamakura, 1976). The crystallization and preliminary crystal data of an iron-containing superoxide dismutase from Pseudomonas ovalis has been reported (Yamakura et al, 1976). 

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