Abstract
Green sulfur bacterium Chlorobium tepidum, an anaerobic photosynthetic bacterium, has an iron-sulfur type reaction center and nitrogenase. In the whole genome of C. tepidum, homologues of iron-sulfur (Fe-S) cluster assembly factors, iscU (or nifU) and iscS (or nifS), are present and they form an operon (CT1994 and CT1995). In a previous study, we reported that purified CT1994 bound a [2Fe-2S] cluster on C-terminal domain. We also reported that another Fe-S cluster was able to reconstitute on N-terminal domain in the presence of iron, sulfide, and reducing agent under an anaerobic conditions. In the present study, we purified CT1995 and found that the purified protein showed desulfurase activity. The Km value is 4.0 µM, and the Vmax value is 8.3 mol sulfide/mol CT1994/min, using L-cysteine as substrate. We also found that reconstitution of Fe-S cluster on N-terminal domain of CT1994 occurred in the presence of CT1995 and L-cysteine instead of sulfide.
