Anaerobic Inductions of Active Forms of Superoxide Dismutases in Escherzchia Coli

Abstract

Escherichio coli growing anaerobically respond to NO⁻₃ with a ∼ 3-fold induction of active FeSOD and a ∼ 5.5-fold induction of an inactive, but activatable form of MnSOD (pro-MnSOD). Paraquat, which mediates anaerobic electron flow to NO₃-, increased the induction of pro-MnSOD to ~ 25-fold. Strains with defects in the SOD genes or which lacked nitrate reductase activity failed to accumulate active or pro-forms of SODS in response to NO₃-± PQ^{+ +}. Diamide caused anaerobic induction of active MnSOD and this effect was also observed in a glutathione-negative strain. These inductions required de novo synthesis of protein, even when cell content of pro-MnSOD had been elevated by exposure to NO₃-+ PQ⁺⁺ prior to addition of diamide.

These results indicate that oxidation of a cell component increases biosynthesis of the SOD gene product and this postulated oxidation can be caused by terminal electron acceptors, such as dioxygen or NO₃-. In addition, it appears that insertion of the correct metal can be rate-limiting, leading to competition by other metals and to the accumulation of inactive, incorrectly substituted pro-forms. Metal insertion may be dependent upon the valence of the metal, which may be influenced, in turn, by the redox status of the cells. Diamide and redox active agents such as ferricyanide may thus allow anaerobic production of active MnSOD by favoring the production of a complexed form of Mn(III) which can compete favorably with other metal cations for the active site of nascent MnSOD.

Key Words:

• Pro-MnSOD
• anaerobic respiration
• paraquat
• reversible resolution
• diarnide.