Homogeneous glycogen phosphorylase b purified from Drosophila melanogaster was activated by phosphorylase kinase isolated from rabbit skeletal muscle. The activation generated phosphorylase a containing 1.1 ± 0.1 phosphoryl group per subunit. Phosphorylase a prepared in this way had a s20w = 8.5S and a subunit molecular mass of 95,000. It could be inactivated (dephosphorylated) by the catalytic subunit of rabbit muscle protein phosphatase-1. The activation-inactivation of phosphorylase by endogenous phosphorylase kinase and phosphatase was also demonstrated in crude homogenates of D. melanogaster. The main protein phosphorylated in the fruit fly homogenate comigrated with purified Drosophila phosphorylse a in sodium dodecyl sulphate (SDS) polyacrylamide gel electrophoresis. Phosphate incorporation into this protein was correlated with phosphorylase activation. Phosphorylase was partially purified from flies fed on [32P]phosphate by 5′-AMP Sepharose affinity chromatography. SDS gel electrophoresis followed by autoradiography revealed that it was phosphorylated in vivo. 20 ± 5% of the total phosphorylase was found to be in the active a form in the anaesthetized insects. Our findings indicate that Drosophila phosphorylase undergoes reversible phosphorylation-dephosphorylation.
- Drosophila melanogaster
- glycogen phosphorylase b and a
- protein phosphorylation