N-Ethylmaleimide (NEM)

Technical Specifications

Product Description & Scientific Applications

N-Ethylmaleimide (NEM) is a sulfhydryl-alkylating reagent historically used to chemically modify cysteine residues in proteins. It reacts with cysteine thiols by nucleophilic addition, a pathway that is faster and more specific than the thioether-forming displacement chemistry of iodoacetamide. NEM is membrane-permeable and available in a radiolabeled form, allowing intracellular and extracellular cysteines to be probed.

Applications

• Cysteine-scanning mutagenesis: In membrane-transporter studies, alkylation of an accessible cysteine mutant by the small, relatively hydrophobic NEM signals that the substituted position lies within the substrate translocation pathway.
• Signal-transduction mapping: Treating the G-protein with NEM blocks its light-induced binding to rhodopsin, letting researchers map cysteines required for this interaction.
• Photoenol Diels–Alder ligation: As an electron-poor dienophile, NEM undergoes a UV-triggered Diels–Alder reaction with a photoenol, part of a dual-gated ligation.
• Radiolabelled tracking: Tritiated NEM follows the time course of cysteine labelling, monitoring incorporation by liquid-scintillation counting.
• Cofactor-assembly block: Equimolar NEM treatment of the sensor protein NreB prevents its reconstitution.

Shipping Destinations

• EU, UK & Switzerland only: Priority delivery, 3–5 business days. UK and Switzerland (DDP): duties and taxes prepaid. Classified as dangerous goods — shipping restrictions apply outside the EU, UK and Switzerland.