EFFECT OF THIOL-BINDING REAGENTS ON THE METABOLISM OF THIOSULFATE AND TETRATHIONATE BY THIOBACILLUS NEAPOLITANUS.

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.