Biochem/physiol Actions L-Leucine chloromethyl ketone (Leu-CMK) is used as a lysosomal cysteine protease inhibitor and as an insulin-like stimulator of lipid synthesis. L-Leucine chloromethyl ketone (Leu-CMK) may be acetylated to generate acetylleucine chloromethyl ketone, an inhibitor of acylpeptide hydrolase.