Novel phosphopeptide derived from GSK-3 recognition motif that acts as a substrate-competitive inhibitor of GSK-3β (IC50 = 150 μM). Displays minimal inhibition of Cdc2, MAPK, PKA, CK2, PKCδ and PKB at 200 μM. Myristoylated version available (L803-mts, Cat. No. 2256).