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

SoxYZ是绿硫菌中硫代硫酸盐依赖性还原cyt c-554所必需的因子。异二聚体SoxYZ，将硫代硫酸盐的氧化产物结合在SoxY的半胱氨酸- sh残基（SoxY- sh）上，作为中间体(SoxY- s)- sso3 -生成(SoxY- s)- sh。部分SoxYZ制剂的活性较低，用硫化物预处理SoxYZ可提高活性。另一方面，DTT、硫代硫酸盐和亚硫酸盐预处理对SoxzYZ的活性无显著影响。用maldi质谱法测定了SoxY的质量。与经硫化物处理的SoxYZ （m/z12852）相比，制备的低活性SoxYZ在TOMES试验中，其SoxY峰的质量数比前者大了约30-80。硫代硫酸盐处理和亚硫酸盐处理的SoxYs的主质量峰也增大了约30-100。这些结果表明，失活的SoxY可能与半胱氨酸S上的-SO3基团结合。

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.