N-Ethylmaleimide (NEM) is widely used as a thiol-blocking agent in biochemical research. It selectively reacts with sulfhydryl groups (-SH) in cysteine residues of proteins, making it valuable for studying protein structure and function by inhibiting disulfide bond formation or enzyme activity dependent on cysteine. It is commonly employed in cell biology to inhibit thiol-dependent enzymes and to block free thiols during protein purification. NEM is also used in studies of membrane transport and vesicle trafficking, where it can inhibit certain ATPases and interfere with endocytosis. In molecular biology, NEM helps stabilize RNA during isolation procedures by inactivating ribonucleases that rely on cysteine residues for activity. Additionally, it serves as a reagent in crosslinking experiments and in the synthesis of other functionalized compounds due to its reactivity toward nucleophiles. Its ability to penetrate cell membranes allows for use in both in vitro and cellular systems.