In vitro regulation of glycogen phosphorylase of the larval fat body of Tenebrio molitor

Abstract

1. 1. Glycogen phosphorylase activity in last larval instar Tenebrio fat body was assayed in the direction of glycogen synthesis in the presence or absence of 5′-AMP. The active form of the enzyme was found to represent 45% of total phosphorylase. 2. 2. Cold exposure of the in vitro fat body strongly activates phosphorylase: after 2 hr of incubation at 4°C, the active form is found to represent 75% of total phosphorylase, ie. 65% increase. When intestinal insulin-like peptide (I.L.P.) is applied after cold activation, this induces a decrease of phosphorylase activity, while I.L.P. fails to modify phosphorylase activity at 25°C. 3. 3. A dose-dependent activation of phosphorylase is induced in vitro by either corpora cardiaca (CC) extracts, or synthetic locust AKH I. The increase of activity of phosphorylase reaches 50% with one pair of CC, and 59% with 10 pmol AKH I. 4. 4. We conclude that larval Tenebrio fat body glycogen phosphorylase may be under hormonal control in vitro.