Bisindolylmaleimide I (BIM I) is a highly selective, cell-permeable, and reversible PKC inhibitor (Ki = 14 nM) that is structurally similar to the poorly selective PKC inhibitor staurosporine . It acts as a competitive inhibitor for the ATP binding site of PKC and shows high selectivity for PKCα, β1, β2, γ, δ, and ε isozymes. BIM I directly inhibits glycogen synthase kinase 3 (GSK3) in primary adipocyte lysates (IC50 = 360 nM) and in GSK3β immunoprecipitates derived from rat epididymal adipocytes (IC50 = 170 nM). It also competitively antagonizes the serotonin (5-HT) receptor subtype 5-HT3 with a Ki value of 61 nM.
