Immunochemical characterization of the modulator protein of the ATP,Mg‐dependent protein phosphatase

Abstract
Polyclonal antibodies raised against the modulator protein of the ATP,Mg‐dependent protein phosphatase completely neutralize all known properties of the purified modulator: inhibition or inactivation of the phosphatase catalytic subunit as well as the kinase FA‐mediated activation of the ATP,Mg‐dependent phosphatase. They do not cross‐react with phosphoinhibitor‐1 or the phosphatase catalytic subunit. Direct analysis of boiled or unboiled skeletal muscle extracts by Western blotting reveals a 32 kDa polypeptide corresponding to the modulator protein as the most dominant protein staining band.