Regulation of fat body glycogen phosphorylase in larval tobacco hornworm, Manduca sexta

Abstract

Activation and inactivation of fat body glycogen phosphorylase was investigated in ligated abdomens of IarvalManduca sexta and in vitro. After maximal activation through Manduca adipokinetic hormone (AKH) or chilling, inactivation of glycogen phosphorylase commenced as soon as the stimulus for the activation was removed indicating that the enzyme system in the fat body is fine-tuned to low phosphorylase activities which is necessary to allow glycogen synthesis. In intact ligated abdomens phosphorylase can be activated repeatedly by either stimulus showing that the fat body system does not lose its responsiveness. It was impossible to achieve complete conversion of the inactive form of phosphorylase into the active form even after administration of AKH and simultaneous chilling.

Carbohydrate metabolism during the pupal molt of the tobacco hornworm, Manduca sexta

“…was unchanged during this developmental stage. The results for larval fat body are also very similar (Siegert, 1992) to the situation reported here. In vivo chilling for 1 or 2 h increased active phosphorylase to approximately 80%, as was found in ligated abdomens.…”

“…The responsiveness can also be tested in vitro using two different salines, as outlined by Siegert (1992). Two sets of experiments were carried out with pharate pupae (day 8) and pupae (day 2).…”

“…Fat body glycogen phosphorylase also responds to chilling; in ligated larval abdomens the enzyme can be activated to 70-80% within 1 h (Siegert, 19921, while in intact adults chilling leads to approximately 40% active phosphorylase (Siegert and Mordue, 1992). The responsiveness can also be tested in vitro using two different salines, as outlined by Siegert (1992). Two sets of experiments were carried out with pharate pupae (day 8) and pupae (day 2).…”

Carbohydrate and lipid metabolism during the last larval moult of the tobacco hornworm, Manduca sexta

“…In both cases fat body glycogen phosphorylase remained activated for more than 24h. The elevation of enzyme activity during the moult was probably brought about by Manduca AKH from the corpora cardiaca, and the peptide was possibly present in the haemolyrnph throughout to maintain a high percentage of active phosphorylase (Siegert, 1992). At this moment there is, however, no direct evidence for the presence of Manduca AKH in the haemolymph.…”

Metabolic and transcriptional responses to starvation are regulated by FOXO in the red flour beetle, Tribolium castaneum

“…Under normal physiological conditions, trehalose remains at a relatively low level (Thompson et al, 1995). In response to starvation, gluconeogenesis and glycogenolysis are stimulated, resulting in the production of trehalose and glucose accompanied by the consumption of triglyceride, protein and glycogen (Becker et al, 1996; Jiang et al, 2019; Koo et al, 2005; Liu et al, 2008; Siegert, 1992; Süren‐Castillo et al, 2014; Thompson et al, 1995; Thompson et al, 2003; Wang et al, 2016). Although trehalose acts as a recovery factor of starvation stress, its in‐depth mechanism remains poorly understood in insects.…”