Juvenile hormone biosynthesis during sexual maturation and after mating in the adult male migratory grasshopper, Melanoplus sanguinipes

Juvenile hormone III is the exclusive juvenile hormone produced by the corpora allata in adult male Melanoplus sanguinipes. For the first 5 days after adult emergence, the rate of juvenile hormone biosynthesis is low, it then increases rapidly to peak on day 7. Between days 7 and 12 the rate declines to that of newly emerged males and then increases again in 14-day insects. In males allowed a single mating on day 7, the rate of juvenile hormone biosynthesis remains elevated at least to day 12.

A rapid method for preparing insect microsomes

The 1000 g supernatant of a tissue homogenate is layered on top of a small (less than 5 ml) sucrose density gradient and centrifuged for 20 min at very high centrifugal forces in a vertical rotor. Microsomes can be recovered rapidly in suspended form from the middle of the gradient, well separated from mitochondria and soluble (cytosolic) components. Applications to cockroach midgut microsomes and mosquito abdominal tissue microsomes are described, and the method is compared to the classical differential centrifugation method. Cytochrome P-450 monooxygenase activities can be measured on microsomes prepared from midgut tissue of 2-3 Diploptera punctata using this method.

Enzymic synthesis of juvenile hormone in locust corpora allata: evidence for a microsomal cytochrome P-450 linked methyl farnesoate epoxidase

Homogenates of corpora allata from adult Locusta migratoria in phosphate-buffered EDTA have been analysed by sucrose-density-gradient centrifugation. Succinate-cytochrome c reductase activity (mitochondrial) bands between d20/4 1.13-1.15, whereas NADPH-cytochrome c reductase and NADPH-dependent methyl farnesoate 10.11-epoxidase activities band identically between d20/4 1.06-1.12. We conclude that the methyl farnesoate epoxidase is exclusively microsomal. Farnesoic acid O-methyltransferase is an exclusively soluble enzyme which stoichiometrically transfers the S-methyl group from S-adenosylmethionine to farnesoic acid. No carboxyl esterase activity was found. Isolated microsomes were used to obtain an apparent Km = 7.7 X 10-6 M for the epoxidase, although substrate solubility limits the rate to 0.5 V. As expected, the product (juvenile hormone III) is chiral (10 R). The epoxidase is inhibited by excess NADP+ and oxidised cytochrome c, but neither inhibited nor synergised by NADH. NADH supports less than 10% of the NADPH rate of epoxidation. The epoxidase is inhibited by a carbon monoxide/oxygen atmosphere, half-maximal inhibition occurring at a CO/O2 ratio of 4.0. This inhibition is reversed by white-light irradiation.

Development of microsomal cytochrome P-450 monooxygenases during the last larval instar of the locust, Locusta migratoria: correlation with the hemolymph 20-hydroxyecdysone titer

Several enzyme activities were measured in microsomes from Malpighian tubules and from fat body of the locust, Locusta migratoria, during the last larval instar and the 20-hydroxyecdysone titer was determined in the hemolymph. Ecdysone 20-monooxygenase, the cytochrome P-450 dependent monooxygenase which converts ecdysone to the active molting hormone 20-hydroxyecdysone had a low activity in the beginning of the instar, but showed a peak in both Malpighian tubules and fat body which coincided with the peak of 20-hydroxyecdysone in the hemolymph. The varying ratios of ecdysone and 20-hydroxyecdysone in L. migratoria hemolymph may therefore be accounted for by these changes in ecdysone 20-monooxygenase activity. The amounts of cytochrome P-450 and the activity of NADPH-cytochrome c reductase also showed a peak on day 5 of the instar, as did the activity of cytochrome P-450 linked lauric acid omega-hydroxylase in fat body microsomes. In larvae experimentally deprived of molting hormone, the activities of the cytochrome P-450 monooxygenases were low. The possible role of ecdysteroids in the control of developmental changes of cytochrome P-450 monooxygenases is discussed.

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.

A specific binding protein for the moulting hormone ecdysterone in locust haemolymph

Specific binding of 3H-ecdysterone to a high mol. wt protein from Locusta migratoria haemolymph was shown by gel filtration. The hormone-protein complex shows a dissociation constant Kd congruent to 3.10(-7) M, and the concentration of binding sites varies during the last larval instar.

[Metabolism of ecdysone in several organs of Carcinus maenas L. incubated in vitro]

Tissues of the crab Carcinus maenas in premolt were incubated in vitro with tritiated ecdysone. The digestive tract, the ovaries, the testis the hepatopancreas and epidermis fragments convert into ecdysterone. This conversion, which does not occur in other organs including the Y organs, is the only important in vitro metabolic pathway of ecdysone observed in this study.

[The hemolymphatic transport of molting hormone during the development of Locusta migratoria L]

Shortly after injection of radio-labelled ecdysone into fifth instar larvae of Locusta migratoria, 20-hydroxy-ecdysone (ecdysterone) is the main hormone found in the blood. Some 10% of the circulating hormone are bound to hemolymph macromolecules. The ratio of bound to free hormone is stage-dependent; it decreases considerably after previous injections of non-labelled ecdysone, but increases in insects in which ecdysone biosynthesis has been blocked by extirpation of the prothoracic glands or selective X-ray treatment of the hemocytopoietic tissue.