Phosphorylase activities in pharate adult and adult tobacco hornworms, Manduca sexta

Abstract

Fat body glycogen phosphorylase in pharate adult and adult tobacco hornworms, Manduca sexta, could only be activated transiently by the indigenous peptide hormone Mas-AKH. Chilling activated phosphorylase in vitro which can be prevented by glucose; other mono- and disaccharides did not reduce activation as much as glucose; derivatives of glucose were also inactive in vitro. In vivo glucose did not prevent phosphorylase activation during chilling when haemolymph concentrations were artificially increased above 100m m. When glucose was injected into previously chilled animals, inactivation of the enzyme was induced even at 0 °C. In intact adults or in fat body pieces in vitro, chilling could only induce phosphorylase activation to 40–50%, but in homogenates 70–90% active form was found after 2h at 25 °C when the kinase was allowed to be active; this is comparable to results obtained in ligated abdomens of larvae and indicates that the chemical nature of phosphorylase and phosphorylase kinase does not change during development. Phosphorylase kinase from adult M. sexta fat body was inactive at 0 °C or activating ligands are required. Mas-AKH does not seem to be a major agent in the activation of phosphorylase in adult M. sexta; enzyme activities can be modulated in vivo and in vitro by changes in glucose concentration of haemolymph or incubation medium.