acetylleucyl-leucyl-norleucinal

**Acetylleucyl-leucyl-norleucinal** is a synthetic tripeptide aldehyde and a potent cell-permeable inhibitor of cysteine proteases. It is best known as "Calpain Inhibitor I" or "ALLN." The compound inhibits calpain I (Ki ≈ 0.19 µM), calpain II (Ki ≈ 0.15 µM), cathepsin L (Ki ≈ 0.5 nM), and other neutral cysteine proteases, with weaker inhibition of cathepsin H and α-chymotrypsin and no inhibition of trypsin[4][5]. Its mechanism involves reversible covalent binding to the active site cysteine residue in target proteases. ALLN has been widely used as a research tool to study the role of calpains in apoptosis, cell cycle progression (notably G1/S and metaphase/anaphase transitions via cyclin B degradation inhibition), neuronal protection from hypoxia/ischemia, immune modulation by inhibiting iNOS transcription in macrophages, stabilization of MHC class I molecules on antigen processing transporters, and prevention of NF-kB activation by blocking IkBα/β degradation[5][7]. It also activates p53-dependent apoptosis in tumor cell lines.

Other names

N-acetylleucylleucylnorleucinalCalpain inhibitor I, LLNL, MG 101, Proteasome Inhibitor V