Native cytosolic protein phosphatase-1 (PP-1S) containing modulator (inhibitor-2) is an active enzyme

FEBS Lett. 1994 May 16;344(2-3):196-200. doi: 10.1016/0014-5793(94)00391-2.


In vitro, the modulator protein (inhibitor-2) slowly converts the catalytic subunit of protein phosphatase-1 (PP-1C) into an inactive 'MgATP-dependent form' that can be reactivated by the transient phosphorylation of modulator with GSK-3/FA. We report here that this modulator-induced inactivation of PP-1C can be blocked by addition (at pH 7.5) of either 0.3 mM NaF or 150 mM NaCl, or by raising the pH to 8.5. Making use of a combination of the latter conditions, we have partially purified a soluble modulator-associated form of PP-1 (PP-1S) from rabbit skeletal muscle as a spontaneously active enzyme that cannot be further activated by kinase GSK-3/FA. These observations argue against a role for the 'MgATP-dependent' form of PP-1S as an inactive reservoir of PP-1C. PP-1S was separated on aminohexyl Sepharose from another active, cytosolic species of PP-1, which appears to be a proteolytic product of the glycogen-bound PP-1G.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adenosine Triphosphate / pharmacology
  • Animals
  • Calcium-Calmodulin-Dependent Protein Kinases / metabolism
  • Cytosol / enzymology
  • Electrophoresis, Polyacrylamide Gel
  • Elongation Factor 2 Kinase
  • Enzyme Activation / drug effects
  • Enzyme Reactivators / pharmacology
  • Hydrogen-Ion Concentration
  • Muscles / enzymology*
  • Phosphoprotein Phosphatases / metabolism*
  • Phosphorylation
  • Protein Phosphatase 1
  • Rabbits
  • Sodium Chloride / pharmacology
  • Sodium Fluoride / pharmacology


  • Enzyme Reactivators
  • Sodium Chloride
  • Adenosine Triphosphate
  • Sodium Fluoride
  • Calcium-Calmodulin-Dependent Protein Kinases
  • Elongation Factor 2 Kinase
  • Phosphoprotein Phosphatases
  • Protein Phosphatase 1