Mechanism of Mercuric Chloride Resistance in Microorganisms

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Abstract
A mercuric ion reducing enzyme from E. coli W 2252 bearing R factor was purified approximately 100-fold by ammonium sulfate fractionation, DEAE-cellulose chromatography and Sephadex G-200 gel filtration. The purified enzyme had a characteristic absorption spectrum, similar to those of flavin compounds. FAD was detected as a component of the purified enzyme as a result of analysis using thin-layer chromatography and D-amino acid oxidase [EC 1.4.3.3] apoenzyme. FAD stimulated the enzymatic oxidation of NADPH by the acid-precipitated enzyme depending on mercuric ions, while FMN did not have such a stimulating effect. Rapid oxidation of NADPH was observed in the presence of both the purified enzyme and HgCl2. Combinations of the purified enzyme and organic mercurials such as mercurochrome or phenylmercuric acetate, however, did not oxidize NADPH. Kμ for HgCl2 was 0.05 mM. NADPH and, to a lesser extent, NADH seemed to act as electron donors for the enzymatic reduction of HgCl2. Various SH compounds such as 2-mercaptoethanol, cysteine, dithiothreitol, and glutathione (reduced form) were effective and essential for the enzyme activity.

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