[4] Each domain contains a covalently bound iron-containing heme molecule separated by a short distance of 8.1 Å which assists with rapid electron transfer.

Step 2 follows with an additional thiosulfate to subsequently form tetrathionate while reducing both hemes and leaving a typical cysteine residue.

Mutant proteins that replace Met209 with asparagine or glycine have similar substrate affinities to the wildtype variant but have much lower specific activities, suggesting that heme 2 is the electron exit point in the last steps of the mechanism.

Here, it is suggested that a high potential iron-sulfur protein (HiPIP) serves as the electron acceptor in the oxidation of both hemes to their initial state.

[12] The sulfur cycle enables a variety of bacteria to utilize generated thiosulfate as an electron donor for aerobic growth and anaerobic carbon dioxide fixation for photosynthesis.

[14] Thus, bacteria have been isolated from mineral deposits and used in the treatment of refractory gold and iron ores and detoxification of industrial waste products, sewage, and soils contaminated with heavy metals.