Studies on the metabolism of a sulfur-oxidizing bacterium V. Comparative studies on sulfur and sulfite oxidizing systems of Thiobacillus thiooxidans<xref ref-type="fn" rid="fn1"><sup>1</sup></xref>

Properties of the oxidation systems of sulfur and sulfite of a sulfur oxidizing bacterium, Thiobacillus thiooxidans, are compared by using various inhibitors. Oxidation of sulfur is inhibited by a low concentration of monoiodoacetic acid, NEM and pCMB. Inhibition by pCMB is diminished by the addition of an equivalent amount of cysteine to that of added pCMB. Although inhibition by pCMB is also observed in the oxidation of sulfite, it is not diminished by the addition of excess cysteine and the extent of inhibition is lower than that in the oxidation of sulfur. Metal chelating agents, such as DDC, 8-hydroxyquinoline, salicylaldoxime and neocuproine have inhibitory effects on the oxidation of sulfur but do not affect the oxidation of sulfite. Carbon monoxide inhibits the oxidation of sulfur photo-irreversibly and the oxidation of sulfite photo-reversibly. Alcohols and organic acids, inhibit the oxidation of both sulfur and sulfite. The cell-free extract prepared by sonic disruption of cells can oxidize sulfite, but not sulfur. The sulfur oxidizing extract can be, however, prepared by disruption under a nitrogen atmosphere. Both the soluble and participate fractions are required for the oxidation of sulfur, while sulfite oxidation is catalyzed by the participate fraction alone.