MECHANISM OF THIOSULFATE OXIDATION BY THIOBACILLUS INTERMEDIUS

Whole cells and cell-free extracts of Thiobacillus intermedius were capable of oxidizing thiosulfate to sulfate without the intermediary formation of polythionates. Two moles of oxygen were consumed for every mole of thiosulfate oxidized and no sulfur accumulated in the reaction mixtures. The mechanism whereby this oxidation occurs seems to involve the action of the following enzymes (a) rhodanese (thio-sulfate:cyanide sulfur transferase, EC 2.8.1.1) since thiocyanate was produced only in the presence of thiosulfate, cyanide and extract (b) sulfite oxidase which oxidized sulfite to sulfate in the presence of ferricyanide or native cytochrome c which were reduced, however the cytochrome was reoxidized by the addition of cytochrome oxidase; and (c) sulfur oxygenase the first stable product of which is sulfite, but for which activity could only be shown with whole cells, probably because of the labile nature of the enzyme in extracts. The results are indicative of a reaction mechanism similar to that in Thiobacillus novellus. © 1969.