Controls on the Biosynthesis of Superoxide Dismutases in E. coli: An Inactive Precursor

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Escherichia coli can produce two types of superoxide dismutases. One of these, the iron enzyme is found in both aerobic and anaerobic cultures; while the second, a manganese enzyme, is ordinarily present only in aerobic cultures and can be strongly induced by hyperoxia, or by viologens and quinones which mediate intracellular production of O2-. The manner in which the cell controls the biosynthesis of the manganese enzyme has been under study but is not yet understood. This lab has reported that addition of an electron sink, such as paraquat plus nitrate, to an anaerobic culture causes production of the manganese enzyme in a form which is not active but which can be activated by addition of Mn(II) under mildly denaturing conditions; followed by removal of the denaturing stress. This is referred to as the pro-enzyme. It has also been shown that anaerobic cells contain another protein which is recognized by an antibody specific for the manganese enzyme, but which cannot be activated as can the pro-enzyme. This protein is referred to this as the prepro-enzyme. Experiments are being conducted to isolate, characterize and study the interconversions of these forms of the manganese-containing superoxide dismutase of E. coli.%%% Superoxide dismutases (SODs) are enzymes that provide defenses against the toxicity of molecular oxygen in living cells. It also protects against other stresses, e.g., ultra- violet radiation and sulfur dioxide exposure. How these enzymes are made is incompletely understood but important. The biosynthesis is probably regulated by environmental factors. This project will elucidate the pathway of enzyme synthesis and activation.***//