The follicle cell epithelium of maturing ovaries of Locusta migratoria: a new biosynthetic tissue for ecdysone

Follicle cells of maturing ovaries of Locusta migratoria are demonstrated to synthesize the moulting hormone ecdysone (2beta,3beta,14alpha,22R,25-pentahydroxy-5beta-cholest-7-en-6-one). Studies of secretory kinetics under in vitro conditions show that the intensity of hormone secretion is strictly dependent on the stage of maturation of the excised ovaries.

Ecdysterone biosynthesis: a microsomal cytochrome-P-450-linked ecdysone 20-monooxygenase from tissues of the African migratory locust

Ecdysone 20-monooxygenase, an enzyme which converts ecdysone to ecdysterone (the major moulting hormone of insects) has been characterized in cell-free preparations of tissues from African migratory locust. The product of the reaction has been identified as ecdysterone on the basis of several microchemical derivatization and chromatographic methods. Ecdysone 20-monooxygenase activity is located primarily in the microsomal fraction which also carries NADPH cytochrome c reductase and cytochrome P-450, as shown by sucrose density gradient centrifugation. Optimal conditions for the ecdysone 20-monooxygenase assay have been determined. The enzyme has a Km for ecdysone of 2.7 x 10(-7) M and is competitvely inhibited by ecdysterone (Ki = 7.5 x 10(-7) M). Ecdysone 20-monooxygenase is a typical cytochrome P-450 linked monooxygenase: the reaction requires O2 and is inhibited by CO, an effect partially reversed by white light. The enzyme is effectively inhibited by several specific monooxygenase inhibitors and by sulfhydryl reagents, but not by cyanide ions. Ecdysone elicits a type I difference spectrum when added to oxidized microsomes. NADPH acts as preferential electron donor. The transfer of reducing equivalents proceeds through NADPH cytochrome c (P-450) reductase: ecdysone 20-monooxygenase is inhibited by cytochrome c. Both NADPH cytochrome c reductase and ecdysone 20-monooxygenase are inhibited by NADP+ and show a similar Km for NADPH. The Malpighian tubules have the highest specific activity of ecdysone 20-monooxygenase, while fat body contain most of the cytochrome P-450 and NADPH cytochrome c reductase.

The identification of an octopaminergic neurone and the modulation of a myogenic rhythm in the locust

An octopaminergic neurone in an insect is demonstrated. This cell (DUMETi) is the dorsal unpaired median neurone which projects to the extensor tibiae muscle of the locust metathoracic leg. Its soma was physiologically identified, isolated and shown to contain about 0.1 pmol of octopamine. Octopamine is about four times more concentrated in the axon than in the soma. The concentration in the soma is at least 800 times more than that in the soma of an identified motoneurone (which controls the fast extensor of the tibia). The effects of DUMETi on a myogenic rhythm in the extensor muscle of the locust metathoracic leg can be mimicked by superfusion with low concentrations of octopamine. The myogenic bundle possesses at least two types of aminergic receptor: one which slows the rhythm (and has a high-affinity for octopamine) and a second which accelerates the rhythm (and has a low-affinity for octopamine but a high-affinity for the indolalkylamine, 5-hydroxytryptamine). The roles of the two receptor types in modulating the rhythm are discussed in relation to the function of the rhythm.

The mechanism of C-20 hydroxylation of alpha-ecdysone in the desert locust, Schistocerca gregaria

1. The C-20 hydroxylation of alpha-ecdysone to produce beta-ecdysone was investigated in the desert locust, Schistocerca gregaria. 2. alpha-Ecdysone C-20 hydroxylase activity was located primarily in the fat-body and Malpighian tubules. The properties of the hydroxylation system from Malpighian tubules investigated further. 3. The enzyme system was mitochondrial, had a pH optimum of 6.5, an apparent Km of 12.5 micron and required O2 and NADPH. 4. The activity of the hydroxylation system showed developmental variation within the fifth instar, the maximum activity corresponding to the maximum tire of endogenous moulting hormone. The significance of these results is assessed in relation to the control of the endogenous titre of beta-ecdysone. 5. The mechanism of the hydroxylation system was investigated by using known inhibitors of hydroxylation reactions such as CO, metyrapone and cyanide. 6. The CO difference spectrum of the reduced mitochondrial preparation indicated the presence of cytochrome P-450 in the preparation. 7. It concluded that the alpha-ecdysone C-20 hydroxylase system is a cytochrome P-450-deendent mono-oxygenase.

[Fucosterol-24,28-epoxide, an intermediate in the oxidative biodegredation of fucosterol to cholesterol by the cricket (Locusta migratoria (R. and F.)]

beta-Sitosterol 1 is metabolised to cholesterol 5 by phytophagous insects. It has been previously shown that fucosterol-24,28 epoxide 3 is transformed into 5 in Locusta migratoria, desmosterol 4 being an intermediate. It is now established that locusts transform [3-3H]fucosterol propionate into the corresponding labelled epoxide 3, recovered as such or as an oxazoline derivative 11.

The metabolism of 3-deoxy-3-fluoro-D-glucose by Locusta migratoria and Schistocerca gregaria

3-Deoxy-3-fluoro-D-glucose (3FG) administered by injection is toxic to adult Locusta migratoria or Schistocerca gregaria (LD50, 4.8 mg/g). temperature-programmed and isothermal gas chromatographic analysis of poisoned locust haemolymph reveals the presence of a fluorinated metabolite identified as 3-deoxy-3-fluoro-D-glucitol (3FGL). The enzymes responsible for the accumulation of this metabolite are located in the fat body of the insect and partially purified as aldose reductase (alditol: NADP+ 1-oxidoreductase, EC 1.1.1.21) and sorbitol dehydrogenase (L-iditol: NAD+ 5-oxidoreductase EC 1.1.1.14) 3FGL is shown to be both a competitive inhibitor of the NAD-linked sorbitol dehydrogenase with Ki 8¿x 10(-2) M as well as a substrate with Km 0.5 M. A kinetic rate equation is derived and verified to account for the kinetic duality of 3FGL. These results partially explain the toxic effects of 3FG and are consistent with the presence of a hitherto undetected sorbitol metabolism in locusts.

Binding and uptake of trypan blue by developing oocytes of Locusta migratoria migratorioides

Resorbing oocytes are heavily stained by trypan blue injected into the haemolymph; this serves as a basis for a quick and convenient method for measuring the degree of resorption. Oocytes in the beginning of their development are most susceptible towards resorptive tendencies. The uptake of trypan blue by normally developing oocytes is proportional to the oocyte surface. From 'double-marker' experiments, in which trypan blue is injected into the haemolymph together with [3H]inulin (which does not bind to the oocyte membrane) it is estimated that the contribution of binding in the interiorization of trypan blue is in the order of 80%, under the conditions given. In vitro incubations show the interaction of trypan blue with the membrane to be electrostatic in nature.

[Histochemical study of the dorso-ventral flight muscles of the locust, Locusta migratoria]

Histochemical studies have been made on the activity of succinic dehydrogenase (SDH), lipase and localization of lipids in flight monofunctional (83, 84 and 113) and bifunctional (118, 119 and 120) muscles of the locust L, migratoria. Three types of muscle fibers were found in the bifunctional flight muscle 120 which differ in their enzymic activity and the intensity of staining by Sudan Black. The activity of SDH and lipase was found to be the highest in fast muscle fibers, and the lowest -- in slow ones. For the first time muscle fibers were described which may be considered as "intermediate" with respect to their structure and histochemical characteristics.