Subunit Structure and Regulation of Protein Phosphatases

PP2A has been isolated in various dimeric and tri-meric forms. It appears that the core structure of PP2A consists of a 36-kDa catalytic and a 65-kDa regulatory subunit and this dimer can associate with a third variable subunit ranging from 54 to 130 kDa (Walter and 

PPl enzymatic forms are present in the cytosolic and particulate fractions of the cell. PPl was purified from the cytosolic fraction of rabbit skeletal muscle in an inactive form and called the MgATP-dependent phosphatase, since it could be activated by incubation with MgATP plus a protein factor identified later as glycogen synthase kinase-3 (Bollen and Stalmans, 

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