In enzymology, a cysteine desulfurase (EC 2.8.1.7) is an enzyme that catalyzes the chemical reaction

L-cysteine + [enzyme]-cysteine ${\displaystyle \rightleftharpoons }$ L-alanine + [enzyme]-S-sulfanylcysteine

Thus, the two substrates of this enzyme are L-cysteine and [enzyme]-cysteine], whereas its two products are L-alanine and [enzyme]-S-sulfanylcysteine.

This enzyme belongs to the family of transferases, specifically the sulfurtransferases, which transfer sulfur-containing groups. The systematic name of this enzyme class is L-cysteine:[enzyme cysteine] sulfurtransferase. Other names in common use include IscS, NIFS, NifS, SufS, and cysteine desulfurylase. This enzyme participates in thiamine metabolism.

As of late 2007, only one structure has been solved for this class of enzymes, with the PDB accession code 1T3I.

• Zheng L, White RH, Cash VL, Jack RF, Dean DR (1993). "Cysteine desulfurase activity indicates a role for NIFS in metallocluster biosynthesis". Proc. Natl. Acad. Sci. U.S.A. 90 (7): 2754–8. Bibcode:1993PNAS...90.2754Z. doi:10.1073/pnas.90.7.2754. PMC 46174. PMID 8464885.
• Mihara H, Esaki N (2002). "Bacterial cysteine desulfurases: their function and mechanisms". Appl. Microbiol. Biotechnol. 60 (1–2): 12–23. doi:10.1007/s00253-002-1107-4. PMID 12382038. S2CID 23172939.
• Frazzon J, Dean DR (2003). "Formation of iron-sulfur clusters in bacteria: an emerging field in bioinorganic chemistry". Curr. Opin. Chem. Biol. 7 (2): 166–73. doi:10.1016/S1367-5931(03)00021-8. PMID 12714048.