DEC-RVRK-CMK (Decanoyl-Arg-Val-Arg-Lys-chloromethylketone) TFA is a peptide-based CMK (chloromethylketone) inhibitor that targets and inactivates the secreted soluble kexin (Kex2) with a Ki value of 8.45 μM. Kex2, a yeast enzyme and a member of the mammalian subtilisin-like proprotein convertase family within the serine protease class, is a calcium-dependent transmembrane protease. The binding mechanism of Kex2 with different CMK inhibitors depends on substrate selectivity, particularly noting the differences in selectivity between lysine and arginine at the P1 position, which influences their varying binding affinities.