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

Abstract

The form of protein phosphatase‐1 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 α and β 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.