Formation of partially phosphorylated glycogen phosphorylase in the fat body of the migratory locust

Abstract Glycogen phosphorylase b partially purified from fat body of migratory locusts was incubated with phosphorylase kinase and [γ- 32 P]ATP. DEAE-Sephacel chromatography revealed the conversion of phosphorylase b (absolute AMP dependence for activity) to almost equal amounts of phosphorylases ab (high AMP dependence) and a (largely AMP independent). Electrophoresis and autoradiography showed the incorporation of 32 P into the ab and a forms, and its absence from phosphorylase b . The labeling of phosphorylases ab and a , both being dimers of identical subunits, corresponded to respectively 1 and 2 mol phosphate incorporated/mol of enzyme. This suggests that in phosphorylase a both subunits are phosphorylated with one single phosphate group/subunit, while in phosphorylase ab only one subunit is phosphorylated.