title: Immobilized inhibitor-1 binds and inhibits protein phosphatase 1.
abstract: Inhibitor-1 is a potent and specific inhibitor of protein phosphatase 1. Phosphorylation by cAMP-dependent protein kinase is required for expression of its inhibitor activity. In the present study, we have used immobilized inhibitor-1 preparations to study the mechanism underlying protein phosphatase 1 inhibition. Protein phosphatase 1 bound to phosphorylated inhibitor-1 covalently coupled to Sepharose or Affi-Gel beads but did not bind to immobilized preparations of dephosphorylated inhibitor-1 or bovine serum albumin. Phosphorylated inhibitor-1 coupled to Sepharose or Affi-Gel beads retained its ability to inhibit protein phosphatase 1, although the apparent IC50 was decreased about 500-fold. The extent of protein phosphatase 1 binding to immobilized phosphorylated inhibitor-1 was comparable to the degree of protein phosphatase inhibition when the inhibitor protein was present at a concentration near the IC50. The efficiency of protein phosphatase 1 binding to immobilized phosphorylated inhibitor-1 was dependent on the inhibitor concentration on the matrix. Taken together these data indicate that the inhibition of protein phosphatase 1 by phosphorylated inhibitor-1 is a consequence of the binding of the inhibitor protein to one or more sites on protein phosphatase 1.
authors.affiliation: Department of Zoology, Iowa State University, Ames 50011-3223.
authors.forename: V M
authors.initials: VM
authors.lastname: Ingebritsen
authors.forename: T S
authors.initials: TS
authors.lastname: Ingebritsen
mesh_terms: D000818:Animals; D001665:Binding Sites; D002352:Carrier Proteins; D002846:Chromatography, Affinity; D004791:Enzyme Inhibitors; D047908:Intracellular Signaling Peptides and Proteins; D009132:Muscles / Q000032:analysis; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors*; D010765:Phosphorylase Phosphatase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D010766:Phosphorylation; D054645:Protein Phosphatase 1; D011506:Proteins / Q000378:metabolism / Q000494:pharmacology*; D011817:Rabbits; D012685:Sepharose / Q000031:analogs & derivatives
chemical_list: D002352:Carrier Proteins; D004791:Enzyme Inhibitors; D047908:Intracellular Signaling Peptides and Proteins; D011506:Proteins; C021042:protein phosphatase inhibitor-1; C032392:Affi-Gel 10; C055194:Affi-Gel 15; D012685:Sepharose; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D010765:Phosphorylase Phosphatase