Thiosulfate from hydrogen sulfite ions

A notable feature of the reduction potentials for the four individual reaction steps in Table XXII is that three of the potentials are as low as that of the hydrogen couple, and the fourth is almost as high as in Oz or nitrate respiration. A large part of the total free energy of the sulfate-to-sulfide reaction seems to be concentrated in the trithionate ion so it can be released in one step. It is possible to speculate that the three low potential steps—reduction of sulfate, sulfite, and thiosulfate—are only maintenance level operations, receiving their electrons from a short chain similar to Fig. 41 which produces no ATP. A longer electron transport chain could operate between approximately —450 and -(-381 mV to carry electrons to trithionate, and several ATP could be generated within this potential gap. 

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