Regulation of protein phosphatase‐1G from rabbit/skeletal muscle: 1. Phosphorylation by cAMP‐dependent protein kinase at site 2 releases catalytic subunit from the glycogen‐bound holoenzyme

Abstract

The glycogen‐associated form of protein phosphatase‐1 (PP‐1G) is a heterodimer comprising a 37‐kDa catalytic (C) subunit and a 161‐kDa glycogen‐binding (G) subunit, the latter being phosphorylated by cAMP‐dependent protein kinase at two serine residues (site 1 and site 2). Here the amino acid sequence surrounding site 2 has been determined and this phosphoserine shown to lie 19 residues C‐terminal to site 1 in the primary structure. The sequence in this region is: (Formula Presented.) At physiological ionic strength, phosphorylation of glycogen‐bound PP‐1G was found to release all the phosphatase activity from glycogen. The released activity was free C subunit, and not PP‐1G, while the phosp..