Glycogen Synthase Kinase 1 (GSK1)

Two phosphopeptides (I and II) were obtained from synthase which had been phosphorylated by GSK-1 and the same pattern was obtained from synthase phosphorylated using cAMPdPK. When phosphopeptide I resulting from the action of GSK-1 was treated with trypsin, three phosphopeptides were observed, whereas when phosphopeptide I proceeding from the action of cAMPdPK was subjected to tryptic hydrolysis, two new phosphopeptides appeared which were different from those originated by glycogen synthase phosphorylated by GSK-1. The tryptic analysis of phosphopeptide II resulting from the action of GSK-1, cAMPdPK, and PhosbK yielded in all cases the same phosphopeptide. GSK-1 is able to phosphorylate at least four sites and that three of those sites are different from two of the three sites phosphorylated by cAMPdPK. In addition GSK-1 and cAMPdPK phosphorylated the same site as PhosbK.