A hydrogen sulfide: ferric ion oxidoreductase (SFORase), which is crucial in sulfur oxidation of T. ferrooxidans AP19-3, oxidizes hydrogen sulfide with Fe 3 + as an electron acceptor to give sulfite ion and Fe 2 +. When washed intact cells of T. ferrooxidans AP19-3 were treated with hydrogen sulfide solution (100 mM) at pH 6.5 for 1 hr, a heat stable reduced sulfur containing protein, which serves as a reduced sulfur compound for purified SFORase to give sulfite, was formed in the plasma membrane of this strain. The protein, which can bind hydrogen sulfide reversibly, was solubilized from plasma membrane with 1% SDS and purified to an electrophoretically homogeneous state. We tentatively named the protein hydrogen sulfide-binding protein (SBP). SBP had an apparent molecular weight of 16,000 in the presence of 1% SDS. One molecule of SBP had 4.5 molecules of iron and could bind 2.3 molecules of hydrogen sulfide.· The hydrogen sulfide bound to SBP was oxidized by a purified SFORase to give sulfite ion, suggesting that SBP is involved in sulfur oxidation of this bacterium.
The use of elemental sulfur (S°) as an energy source by T. ferrooxidans API9-3 was completely inhibited by above 108mMof Fe2+ added to S°(l %)-salts medium, in which about 0.6mM Fe2+ remained after 30 days cultivation without being oxidized. In contrast, the use of Fe2 + by this strain was not inhibited by S°. It was found that specific activities of hydrogen sulfide: ferric ion oxidoreductase (SFORase) and sulfite : ferric ion oxidoreductase, which are crucial in sulfur and sulfite oxidations of this strain, were completely inhibited by 20 mmand 1 mMFe2 + , suggesting that this may be a main cause for the cells not using sulfur as an energy source. The SFORaseactivity of the cells incubated with S°-Fe2+-salts medium decreased to 39% of that in control cells without Fe2+, suggesting that Fe2 + added to the mediuminhibits a sulfite : ferric ion oxidoreductase, and as a results sulfite ions are accumulated in the cells and this damages the SFORase. Sodium sulfite completely inhibited cell growth on S°-salts medium at 0.1 mM, but not on iron-salts medium.
A hydrogen sulfide : ferric ion oxidoreductase (SFORase), which is crucial in sulfur oxidation of T. ferrooxidans AP19-3, oxidizes hydrogen sulfide with Fe3 + as an electron acceptor to give sulfite ion and Fe2 +. Whenwashed intact cells of T.ferrooxidans AP19-3 were treated with hydrogen sulfide solution (100him) at pH 6.5 for 1 hr, a heat stable reduced sulfur containing protein, which serves as a reduced sulfur compound for purified SFORaseto give sulfite, was formed in the plasma membrane of this strain. The protein, which can bind hydrogen sulfide reversibly, was solubilized from plasma membrane with 1%SDS and purified to an electrophoretically homogeneous state. We tentatively named the protein hydrogen sulfide-binding protein (SBP). SBP had an apparent molecular weight of 16,000 in the presence of 1% SDS. One molecule of SBP had 4.5 molecules of iron and could bind 2.3 molecules of hydrogen sulfide. The hydrogen sulfide bound to SBP was oxidized by a purified SFORase to give sulfite ion, suggesting that SBP is involved in sulfur oxidation of this bacterium.
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