Catalyzes the removal of elemental sulfur from cysteine to produce alanine. It supplies the inorganic sulfur for iron-sulfur (Fe-S) clusters. May be involved in the biosynthesis of molybdenum cofactor. [sulfur carrier]-H + L-cysteine = [sulfur carrier]-SH + L-alanine Binds ISCU/NIFUN. Forms a complex with LYRM4. Interacts with HSPA9. Ubiquitous. Belongs to the class-V pyridoxal-phosphate-dependent aminotransferase family. NifS/IscS subfamily.