Protein phosphatase inhibitor-1(IPP-1) plays an important role in the regulation of glycogen metabolism through inhibition of type-1 protein serine/threonine phosphatase(PP1) activity, and it has been implicated in the regulation of cell growth. IPP-1 activation may impose cAMP control over proteins that are not directly phosphorylated by PKA. In the presence of calcium, PPI-1 is inactivated by calcineurin (or PP2B).