Plays a role in regulating the phosphorylation of other proteins, and is itself phosphorylated by a cyclic AMP-dependent protein kinase at Threonine 35. In addition, the proline-directed kinases Cdk1, Cdk5, and mitogen-activated protein kinase (MAPK) mediate in vitro phosphorylation of IPP-1 at the phylogenetically conserved position Serine 67.