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Chemical structure of N-ethylmaleimide

N-Ethylmaleimide (NEM) is a chemical derivative of maleic acid imide or maleic acid. It is used to irreversibly inhibit the formation of cystine linking in proteins. It has been observed that after addition of NEM vesicular transport was blocked. After identification of the responsible protein it was called N-ethylmaleimide sensitive fusion protein (NSF). 20 to 25 mM of NEM is also used in lysis buffer to inhibit de-sumoylation of proteins for Western Blot analysis. NEM is also used as an inhibitor of deubiquitinases.