Thiosulfate, intracellular sulfur, and acetate utilization by Chromatium D were inhibited by iodoacetamide, N-ethylmaleimide (NEM), p-hydroxymercuribenzoate (CMB), and HgCl₂. Pyruvate, sulfide, and sulfite utilization were insensitive to iodoacetamide, and were less sensitive to NEM, CMB, and HgCl₂ than thiosulfate, intracellular sulfur, and acetate utilization. The effect of the thiol-binding reagents on cell viability was dependent upon the method of exposure; cells exposed to the thiol-binding reagents in the presence of thiosulfate were protected from the killing action of these agents, but not from their inhibitory effect. Although the inhibitory effects of the thiol-binding reagents could, in some cases, be attributed to their effect on viability, they were inhibitory under conditions where viability was unaffected. The most straightforward results were obtained with iodoacetamide, which revealed a sharp separation in sensitivities between the systems tested but had no effect on cell viability. The results are consistent with the hypothesis that thiols are involved in thiosulfate, intracellular sulfur, and acetate utilization.

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