GSK3 is a serine/threonine kinase with a proline-directed substrate preference. Apart from phosphorylating and inhibiting glycogen synthase (GS), various other substrates for GSK3 have been identified that includes protein phosphatase inhibitor 2, ATP-citrate lyase, tau protein, beta-catenin, c-Myc, c-Jun, cAMP response element-binding protein, CCAAT/enhancer-binding protein- , and initiation factor eukaryotic initiation factor. In human, GSK3 exists in two isoforms a-isoform and b-isoform, encoded by two distinct genes located on chromosomes 19q13.1