The study of thiosulfate oxidation multi-enzyme system in the green sulfur bacterium Chlorobaculum tepidum

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SoxYZ is the factors indispensable for thiosulfate-dependent reduction of cyt c-554 from the green sulfur bacterium Chlorobaculum tepidum. Heterodimeric SoxYZ that binds oxidized product of thiosulfate on the cysteinyl-SH residue of SoxY (SoxY-SH) as the intermediate (SoxY-S)-SSO3- to yield (SoxY-S)-SH. Some preparations of SoxYZ showed low activity, and pretreatment of SoxYZ with sulfide increased the activity. On the other hand, pretreatments of SoxzYZ with DTT, thiosulfate and sulfite had no significant effects on the activity. We measured the mass of SoxY by MALDI-mass spectrometry. Compared with the sulfide-treated SoxYZ (m/z12852), the peaks of SoxY of as prepared SoxYZ with low activity in the TOMES assay had a mass number larger by about 30-80 than that of the former. The main mass peaks of both thiosulfate-treated and the sulfite-treated SoxYs also were larger by about 30-100. These results suggest that the inactive SoxY possibly binds –SO3 group on the cysteinyl S.