N-Ethylmaleimide

N-Ethylmaleimide (NEM) is derived from maleic acid and can alkylate free sulfhydryl groups. It is a protein sulfhydryl modifier that can be used to modify cysteine residues in proteins and peptides ^[1]. N-Ethylmaleimid inhibits prolyl endopeptidase with an IC₅₀ value of 6.3 μM ^[2]. N-Ethylmaleimid is an irreversible inhibitor of all cysteine ​peptidases, and alkylation occurs at the active site thiol group ^[3]. N-Ethylmaleimid has also been used as an inhibitor of deubiquitinase ^[4].

In vitro, treatment of vascular smooth muscle cells with N-Ethylmaleimid (20 μM) effectively inhibited the phosphorylation of Akt Ser-473, Akt Thr-308, p70S6K, ribosomal protein S6, 4E-BP1, BAD and FKHR-L1 stimulated by platelet-derived growth factor-BB (PDGF-BB) ^[5].

In vivo, N-Ethylmaleimid (10 mg/kg, subcutaneous injection) treatment of male Wistar rats with acute gastric ulcer induced by anhydrous ethanol injection increased the lesion area of ​acute gastric ulcer and weakened the gastroprotective effect of momordica charantia Ic^[6].

References:
[1] Robotham A C, Kelly J F. Detection and quantification of free sulfhydryls in monoclonal antibodies using maleimide labeling and mass spectrometry[C]//MAbs. Taylor & Francis, 2019, 11(4): 757-766.
[2]Moriyama A, Nakanishi M, Sasaki M. Porcine muscle prolyl endopeptidase and its endogenous substrates[J]. The Journal of Biochemistry, 1988, 104(1): 112-117.
[3]Schirmeister T. New peptidic cysteine protease inhibitors derived from the electrophilic α-amino acid aziridine-2, 3-dicarboxylic acid[J]. Journal of medicinal chemistry, 1999, 42(4): 560-572.
[4]Sarkar K, Sadhukhan S, Han S S, et al. SUMOylation-disrupting WAS mutation converts WASp from a transcriptional activator to a repressor of NF-κB response genes in T cells[J]. Blood, The Journal of the American Society of Hematology, 2015, 126(14): 1670-1682.
[5]Yellaturu C R, Bhanoori M, Neeli I, et al. N-Ethylmaleimide inhibits platelet-derived growth factor BB-stimulated Akt phosphorylation via activation of protein phosphatase 2A[J]. Journal of Biological Chemistry, 2002, 277(42): 40148-40155.
[6]Matsuda H, Li Y, Yoshikawa M. Roles of capsaicin-sensitive sensory nerves, endogenous nitric oxide, sulfhydryls, and prostaglandins in gastroprotection by momordin Ic, an oleanolic acid oligoglycoside, on ethanol-induced gastric mucosal lesions in rats[J]. Life Sciences, 1999, 65(2): 27-32.

N-乙基马来酰亚胺（N-Ethylmaleimide；NEM）衍生于马来酸，能烷基化游离巯基，是一种蛋白质巯基修饰剂，可用于修饰蛋白质和多肽中的半胱氨酸残基^[1]。N-Ethylmaleimid对脯氨酰内肽酶有抑制作用，IC₅₀值为6.3μM^[2]。N-Ethylmaleimide是所有半胱氨酸肽酶的不可逆抑制剂，烷基化发生在活性位点硫醇基团处^[3]。N-Ethylmaleimid也被用作去泛素酶的抑制剂^[4]。

在体外，N-Ethylmaleimid（20 μM）处理血管平滑肌细胞，可有效抑制血小板衍生生长因子-BB（PDGF-BB）刺激的Akt Ser-473、Akt Thr-308、p70S6K、核糖体蛋白S6、4E-BP1、BAD和FKHR-L1磷酸化^[5]。

在体内，N-Ethylmaleimid（10mg/kg，皮下注射）处理无水乙醇注射致急性胃溃疡雄性Wistar大鼠，增加了急性胃溃疡的病变面积并减弱了苦瓜素Ic的胃保护作用^[6]。