SUMMARY: A thiosulphate-oxidizing system of grown on thiosulphate was studied using intact cells, crude cell-free extracts and isolated membrane vesicles. All active preparations oxidized thiosulphate to sulphate, without intermediary accumulation of polythionates, consuming two moles of oxygen for every mole of thiosulphate oxidized. Less active cell-free preparations required reduced glutathione, NADH or sulphite for thiosulphate oxidation. An active membrane-associated thiosulphate-oxidizing system from crude cell-free extracts was isolated by either Sepharose 4B column chromatography or differential centrifugation. The isolated multi-enzyme complex system exhibited high specificity for thiosulphate with an apparent value of 0.12 mM. Enzyme activity was optimum at pH 7.5 and 25 °C. The system was sensitive to oxygen, storage at certain temperatures and freezing. Inhibition studies indicated that active sulphydryl groups and an electron transport chain were involved during thiosulphate oxidation. Electron micrographs of active crude extracts and the isolated membrane complex after negative staining showed the presence of spherical structures with a diameter of about 0.1 to 0.4 μm. An ultra-thin section of the membrane complex revealed that the large spherical particles observed in the negatively stained preparations were aggregated structures consisting of smaller vesicles 0.02 to 0.05 μm in diameter.


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