MLCK inhibitor peptide 18 is a myosin light chain kinase (MLCK) inhibitor with an IC₅₀ of 50 nM, and inhibits CaM kinase II only at 4000-fold higher concentrations. IC50 & Target: IC50: 50 nM (MLCK)^[1] In Vitro: MLCK inhibitor peptide 18 has a selective effect on peptide substrate utilization by MLCK, does not interfere with kinase activation by CaM, does not have significant inhibitory activity with the closely related CaMPKII, and does not inhibit PKA^[1].