Abstract
Green sulfur bacteria grow phototrophically using sulfide as well as thiosulfate as electron donor. We purified three proteins which are involved in oxidation of thiosulfate from Chlorobaculum (formally Chlorobium) tepidum cells. For electron transfer from thiosulfate to cytochrome c-554, SoxY, SoxZ, SoxAX-CT1020 were indispensable in the reaction mixtures. As for CT1020, which is a subunit of heterotrimer of SoxAX-CT1020, the presence of this component is limited to the species of green sulfur bacteria which have an ability of thiosulfate oxidation. Other thiosulfate oxidizing bacteria have heterodimer SoxAX without CT1020. To investigate whether CT1020 is essential for the thiosulfate oxidation in C. tepidum, we expressed SoxA, SoxX and CT1020 in Escherichia coli respectively. The reaction mixture contained three recombinant proteins showed almost the same thiosulfate oxidation activity as that of purified C.tepidum cells, however, if one of three was omitted from the reaction mixture, no activity was observed.
