Effect of Thiol-Binding Reagents on the Metabolism of Thiosulfate and Tetrathionate by Thiobacillus neapolitanus

Abstract

Trudinger , P. A. (Division of Plant Industry, Canberra, Australia). Effect of thiol-binding reagents on the metabolism of thiosulfate and tetrathionate by Thiobacillus neapolitanus . J. Bacteriol. 89: 617–625. 1965.—Iodoacetamide, N -ethyl maleimide (NEM), p -chloromercuribenzoate (CMB), Mercurochrome, and HgCl 2 inhibited the oxidation of thiosulfate to sulfate by Thiobacillus neapolitanus; tetrathionate accumulated under these conditions. High concentrations of the thiol-binding reagents lowered the rate of oxidation of thiosulfate to tetrathionate; inhibition by CMB was reversed by high concentrations of thiosulfate. Relatively low concentrations of the thiol-binding reagents completely inhibited the oxidation and anaerobic metabolism of tetrathionate. Similar reagents had no effect on a soluble thiosulfate-oxidizing enzyme. Inhibition by thiol-binding reagents was overcome by washing the bacteria with Na 2 S or thioethanol after their exposure to the inhibitors. Under some conditions, the addition of thiosulfate or tetrathionate to bacterial suspensions before the addition of the thiol-binding reagents prevented the inhibition of thiosulfate and tetrathionate metabolism by these reagents. Thiosulfate catalyzed a rapid chemical breakdown of NEM and reacted with iodoacetamide. A complex between thiosulfate and mercuribenzoate was demonstrated. Three types of thiol group appear to be associated with the metabolism of thiosulfate and tetrathionate; one of these types may be located at the bacterial cell membrane. The results are consistent with the hypothesis that thiols (or disulfide groups) are binding sites for the substrates.