This peptide is used to block Phospho-GSK-3a (Ser21) Rabbit mAb #G8170-40D5 reactivity. Glycogen synthase kinase-3 (GSK-3) was initially identified as an enzyme that regulated glycogen synthesis in response to insulin (1). GSK-3 is a ubiquitously expressed serine/threonine protein kinase that phosphorylates and inactivates glycogen synthase. GSK-3 is a critical downstream element of the PI3 kinase/Akt cell survival pathway, and its activity can be inhibited by Akt-mediated phosphorylation at Ser21 of GSK-3a and Ser9 of GSK-3b (2,3). GSK-3 has been implicated in the regulation of cell fate in Dictyostelium, and is a component of the Wnt signaling pathway required for Drosophila, Xenopus and mammalian development (4). GSK-3 has been shown to regulate cyclin D1 proteolysis and subcellular localization (5). Quality Control: The quality of the peptide was evaluated by reversed-phase HPLC and by mass spectrometry. The peptide blocks Phospho-GSK-3a (Ser21) Rabbit mAb #G8170-40D5 by immunohist