Regulation of glycogenolysis in the locust fat body during flight

Abstract

Abstract~Glycogen reserves in the fat body of Locusta migratoria decrease dramatically during the first two hours of flight. In fat body of rested locusts only 10~o of glycogen phosphorylase occurs in the active form. The enzyme is activated significantly during flight, when up to one-third of the total phosphorylase becomes active. Plaosphorylase activation can also be accomplished by injection of corpus cardiacum extracts, to give a maximum of circa 75~o active enzyme. Locust fat body is shown to contain protein kinase activity, which can be activated both by cyclic AMP and cyclic GMP. Apparent Ka-values are 0.13/~M for cyclic AMP and 0.16/~M for cyclic GMP. Results are discussed in relation to regulation of substrate utilization during flight.

Insect flight muscle metabolism

“…In Locusta, flight activity as well as corpora cardiaca extracts elevate the level of cAMP in fat body (G/ide and Holwerda, 1976), which also contains cyclic nucleotide-dependent protein kinase (Pines and Applebaum, 1978;Van Marrewijk et al, 1980). However, the actual mechanism of phosphorylase activation by adipokinetic hormone still remains to be elucidated.…”

“…The steady state of haemolymph trehalose is sustained by the mobilization of other carbohydrate stores. Fat body glycogen is the main source, its concentration decreasing at a rate sufficient to account for almost two-thirds of the total trehalose utilized between 30 and 120min of flight (Van Marrewijk et al, 1980). Thus one-third must be derived from other sources, part of which will be provided by the glycerol that is liberated by hydrolysis of diacylglycerol, as will be discussed in section 5.2.…”

“…Locust flight also induces a rapid activation of fat body phosphorylase, the active form increasing from less than 10~o of total phosphorylase in resting Insect flight muscle metabolism 249 locusts to about 30~ during sustained flight (Van Marrewijk et al, 1980). The mode of action of the hypertrehalosemic hormone in the fat body has been investigated extensively in Periplaneta.…”

Hypertrehalosaemic and hyperlipaemic responses to adipokinetic hormone in fifth larval instar locusts, Locusta migratoria

“…Glycogen phosphorylase activity was measured spectrophotometrically in the direction of glycogen degradation as described previously (Van Marrewijk et al, 1980a). Active phosphorylase was assayed in the absence of Y-AMP, whereas total phosphorylase was measured in the presence of 2 mM Y-AMP.…”

“…Extracts from corpora cardiaca (CC), and synthetic adipokinetic hormone (AKH) evoke hyperlipaemia in locusts also, but they have no influence on haemolymph carbohydrate levels (for reviews, see Beenakkers et al, 1981aBeenakkers et al, , b, 1983. However, in the locust fat body flight activity results in the activation of glycogen phosphorylase, the enzyme determining the rate of glycogenolysis (Van Marrewijk et al, 1980a), This phosphorylase activation is needed to meet the enhanced turnover rate of haemolymph trehalose during sustained flight . Fat body phosphorylase is also activated upon injection of CC-extracts (Bcenakkers et al, 1978), and recently this effect of the CC on phosphorylase was shown to be due virtually entirely to AKH (Van Marrewijk and Beenakkers, 1982;.…”