Studies on the metabolism of a sulfur-oxidizing bacterium VIII. Purification and characterization of soluble components indispensables for sulfur oxidation by Thiobacillus thiooxidans

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The soluble fraction required for the sulfur-oxidizing system of Thiobacillus thio-oxidans was resolved into two components through ammonium sulfate fractionation, Amberlite CG-50, DEAE cellulose column chromatography and Sephadex gel filtration. Both components (A and B) were indispensable for the sulfur-oxidizing system. Component A with a molecular weight of 120,000 is a non-heme iron protein. The absorption maximum of the oxidized form was at 410 nm but was shifted to 420 nm by reduction. Component B is a new flavoprotein containing non-heme iron. Although the same absorption change was seen at 410 nm (as with component A) the shoulder at 485 nm in the oxidized form disappeared upon reduction. The molecular weight of component B was calculated as 23,000 using the gel filtration method. The sulfur-oxidizing activity of the reconstituted system was markedly inhibited by such metal-chelating agents as EDTA, DDC and o-phenanthroline. Several nucleotides, which are known flavoprotein inhibitors, inhibited the sulfur-oxidizing activity. Removal of the Fe in the soluble fraction components by KCN or DDC treatment de-creased the sulfur-oxidizing activity of the reconstituted system. Based on these evidences we concluded that iron and flavin in the soluble components may have an important role in the elemental sulfur-oxidizing system of Thiobacillus thiooxidans.
日本植物生理学会の論文