Effect of ligands on Drosophila phosphorylase a as monitored by its enzymic inactivation

The dephosphorylation of Drosophila phosphorylase a with the catalytic subunit of fruit-fly protein phosphatase-1 was inhibited by AMP, IMP, ADP, ATP, glucose-6-P, glucose-1-P and UDPG. Glucose, caffeine and glycogen did not influence the reaction. The inhibitory effect of AMP was reduced by glucose and caffeine. The above ligands acted through the modification of phosphorylase a conformation. This conclusion was drawn from the ligands' effect on the dephosphorylation of phosphohistone by Drosophila phosphatase-1 and on the tryptic digestion of fruit-fly phosphorylase a.