Purification of the hepatic glycogen-associated form of protein phosphatase-1 by microcystin-Sepharose affinity chromatography

The form of protein phosphatase-l associated with hepatic glycogen (PP1G) was purified to near homogeneity from rat liver by affinity chromatography on microcystin-Sepharose and gel-filtration, The enzyme is a heterodimer consisting of the catalytic subunit of PP1 (the alpha and beta isoforms) complexed to a 33 kDa glycogen-binding (G(L)) subunit. The G(L) subunit binds phosphorylase a with high affinity, and is responsible for the enhanced dephosphorylation of glycogen synthase by PP1G and its allosteric inhibition by phosphorylase a.