Purified by Ni/NTA agarose chromatography (≥ 85%, Verified by SDS-PAGE and Coomassie Blue stain). Glycogen Synthase Kinase-3 (GSK-3) is a serine/threonine kinase that was first characterized by its role in intermediary metabolism. The enzyme is the mammalian homolog of the zeste-white3 (shaggy) homeotic gene of Drosophila melanogaster and has been implicated in the regulation of the c-Jun/AP-1 transcription factor. In mammals, this protein serine kinase is encoded by two related genes called GSK-3a (51kD) and b (46kD). Genetic and biochemical evidence now indicates that GSK-3 plays a role in intracellular signaling pathways. For example, during insulin and growth factor signaling the GSK-3 beta isoform becomes phosphorylated on its N-terminal serine-9 residue, presumably by either the action of MAPKAP Kinase-1 (p90 S6 kinase, Rsk-2) or p70 S6 kinase. Such phosphorylation of GSK-3 blocks its ability to phosphorylate c-Jun, protein phosphatase inhibitor 2 or the GSK-3 substrate peptide.