cAMP-regulated phosphoprotein 19, also known as ARPP19, is protein phosphatase inhibitor that specifically inhibits protein phosphatase 2A (PP2A) during mitosis. When phosphorylated at Ser-62 during mitosis, specifically interacts with PPP2R2D (PR55-delta) and inhibits its activity, leading to inactivation of PP2A, an essential condition to keep cyclin-B1-CDK1 activity high during M phase. This protein may indirectly enhance GAP-43 expression. Recombinant human ARPP19 protein, fused to His-tag at N-terminus, was expressed in E.coli and purified by using conventional chromatography techniques.