A soluble thiosulphate-oxidizing multi-enzyme system, precipitated from a crude cell extract of Thiobacillus A2 with ammonium sulphate, has been resolved into four essential components by DEAE-Sepharose chromatography, gel filtration of Sephadex G-100 and G-200, hydrophobic interaction chromatography on phenyl-Sepharose and preparative isoelectric focusing. Oxidation of thiosulphate to sulphate coupled to the reduction of horse-heart cytochrome c as electron acceptor was catalysed by two colourless proteins (enzyme A: Mr, 16000; and enzyme B: Mr, 64000). cytochrome c552.5 (Mr, 32000) and cytochrome c551 (Mr, 300000). Enzymes A and B were purified 110- and 280-fold, respectively. Sulphite: cytochrome c oxidoreductase was also purified 660-fold. The mechanism of action of the system is discussed.
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