PURIFICATION AND CHARACTERIZATION OF BOVINE HEART GLYCOGEN-SYNTHASE KINASE-3

Glycogen Synthase Kinase-3 (GSK-3) was isolated from bovine heart tissue extracts by a procedure involving ammonium sulfate fractionation, followed by chromatography on phosphocellulose, Cibacron blue 3GA-agarose, DEAE-Sephacel, CM-Sepharose, heparin-agarose, myelin basic protein-Sepharose, and LiChrospher 1000 COO-. GSK-3 was identified by its activation of protein phosphatase-1(i) (PR-1(i)). The purified enzyme had a specific activity of 25,500 units of protein phosphatase-1(i) activated/mg protein. The enzyme is an asymmetric monomeric protein of 53 kDa. The molecular size and retention of activity after autophosphorylation indicated that the isolated enzyme was the GSK-3 alpha-isoform.