N-Ethylmaleimide-d5 is the deuterium labeled N-Ethylmaleimide. N-Ethylmaleimide (NEM), a reagent that alkylates free sulfhydryl groups, is a cysteine protease inhibitor[1]. N-ethylmaleimide specific inhibits phosphate transport in mitochondria[2]. N-Ethylmaleimide is also a deubiquitinating enzyme inhibitor[3].