Catalyzes the removal of elemental sulfur from cysteine to produce alanine. Supplies the inorganic sulfur for iron-sulfur (Fe-S) clusters. [sulfur carrier]-H + L-cysteine = [sulfur carrier]-SH + L-alanine Threefold increase in the catalytic activity in the presence of FH (frataxin) (PubMed:22511606). 30-fold increase in the catalytic activity in the presence of SUFE1 (PubMed:16437155). Optimum pH is 8.5. Interacts with FH (PubMed:22511606). Interacts with SUFE1 (PubMed:16437155). A number of isoforms are produced. According to EST sequences. Lethal when homozygous. Belongs to the class-V pyridoxal-phosphate-dependent aminotransferase family. NifS/IscS subfamily.