scholarly journals The mechanism of C-20 hydroxylation of α-ecdysone in the desert locust, Schistocerca gregaria

1977 ◽  
Vol 168 (3) ◽  
pp. 513-520 ◽  
Author(s):  
P Johnson ◽  
H H Rees
Keyword(s):  
Schistocerca Gregaria ◽  
Fat Body ◽  
Difference Spectrum ◽  
Maximum Activity ◽  
Malpighian Tubules ◽  
Desert Locust ◽  
Ph Optimum ◽  
Developmental Variation ◽  
Moulting Hormone ◽  
Cytochrome P 450

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.

Amino-Acid Metabolism in Locust Tissues

1957 ◽  
Vol 34 (2) ◽  
pp. 276-289
Author(s):  
B. A. KILBY ◽  
ELISABETH NEVILLE
Keyword(s):  
Amino Acid ◽  
Amino Acid Metabolism ◽  
Acid Metabolism ◽  
Schistocerca Gregaria ◽  
Fat Body ◽  
Malpighian Tubule ◽  
Malpighian Tubules ◽  
Acid Oxidase ◽  
Amino Acid Oxidase ◽  
Mitochondrial Fractions

1. Homogenates of fat-body of Schistocerca gregaria Forsk. were shown to catalyse transamination reactions between α-ketoglutarate and numerous α-amino acids. The aspartate/glutamate and alanine/glutamate transaminases were the most active. They were present in both the ‘soluble’ and the mitochondrial fractions of fat-body cells and also in Malpighian tubules and mid-gut wall. The other transaminases in the fat-body were confined to the mitochondrial fraction. 2. Fat-body, Malpighian tubule and mid-gut wall homogenates were able to convert glutamic acid into glutamine, a compound which could also act as an amino-group donor in some transamination reactions. 3. A glutamate-cytochrome c reductase system which involved diphosphopyridine nucleotide was present in fat-body. 4. Fat-body contained an active arginase, but urease could not be detected. A D-amino-acid oxidase was present, together with a less active L-amino-acid oxidase. 5. In general, it appears that amino-acid metabolism in the locust resembles that in higher animals.

Some effects of the nematode Mermis nigrescens upon carbohydrate metabolism in the fat body of its host, the desert locust Schistocerca gregaria

1971 ◽  
Vol 49 (4) ◽  
pp. 431-434 ◽  
Author(s):  
Roger Gordon ◽  
John M. Webster ◽  
David E. Mead
Keyword(s):  
Carbohydrate Metabolism ◽  
Glycogen Phosphorylase ◽  
Schistocerca Gregaria ◽  
Fat Body ◽  
Constant Level ◽  
Desert Locust ◽  
Carbohydrate Levels ◽  
Fat Bodies

Adult desert locusts were experimentally infected with 50 Mermis nigrescens ova and changes in the fat body carbohydrate levels and glycogen phosphorylase activities recorded. At both 2 and 3 weeks after infection, the parasitism caused a significant reduction in the level of glycogen and non-glycogen carbohydrates in the host fat body, together with a progressive depletion of active and inactive glycogen phosphorylases. By feeding extensively upon the blood carbohydrates of the host, the developing nematode deprives the fat body of carbohydrates and thereby effects a reduction in glycogenesis by the host fat body. Increased catabolism (and (or) decreased anabolism) of the fat body phosphorylases, together with a possible suppression of the host "hyperglycaemic factor" by the nematode, prevent further glycogenolysis by the fat bodies of mermithid-infected locusts and allow a low, constant level of fat body glycogen to be maintained in these insects.

Rectal Absorption in the Desert Locust, Schistocherca Gregaria Forskål

1964 ◽  
Vol 41 (1) ◽  
pp. 69-80
Author(s):  
J. E. PHILLIPS
Keyword(s):  
Water Balance ◽  
Osmotic Pressure ◽  
Schistocerca Gregaria ◽  
Tap Water ◽  
Ionic Concentration ◽  
Malpighian Tubules ◽  
Desert Locust ◽  
Ionic Regulation ◽  
Rectal Absorption ◽  
Salt And Water Balance

1. The physiology of the excretory system and its role in salt and water balance have been studied in the desert locust, Schistocerca gregaria. 2. Collections and analyses were made of hindgut fluid (derived from the Malpighian tubules) and rectal fluid from locusts kept under various dietary régimes. 3. In starved locusts supplied with tap water very little fluid accumulates in the rectum, the output of the Malpighian tubules being almost completely reabsorbed. Relatively more salt than water is reabsorbed with the result that the rectal fluid attains a lower ionic concentration but higher osmotic pressure than the haemolymph. No fluid is voided. 4. In starved locusts supplied with hypertonic saline the rectum is distended with, fluid which has an osmotic pressure and ionic concentration considerably above that of the haemolymph. Very little fluid is voided. 5. Substantial elimination of fluid from the rectum occurs only in fed locusts, in association with the voiding of faeces. 6. These results are discussed in relation to the mechanism of osmotic and ionic regulation.

scholarly journals Proctolin degradation by membrane peptidases from nervous tissues of the desert locust (Schistocerca gregaria)

1987 ◽  
Vol 245 (2) ◽  
pp. 365-370 ◽  
Author(s):  
R E Isaac
Keyword(s):  
Schistocerca Gregaria ◽  
Physiological Role ◽  
Hydrolytic Activity ◽  
Mitochondrial Fraction ◽  
Membrane Preparation ◽  
Aminopeptidase Activity ◽  
Synaptic Membrane ◽  
Desert Locust ◽  
Ph Optimum ◽  
Enzyme Preparations

The hydrolysis of the insect neuropeptide proctolin (Arg-Tyr-Leu-Pro-Thr) by enzyme preparations from the nervous tissue of the desert locust (Schistocerca gregaria) was investigated. Neural homogenate degraded proctolin (100 microM) at neutral pH by cleavage of the Arg-Tyr and Tyr-Leu bonds to yield Tyr-Leu-Pro-Thr, Arg-Tyr and free tyrosine. Arg-Tyr was detected as a major metabolite when the aminopeptidase inhibitors amastatin and bestatin were present to prevent Arg-Tyr breakdown. Around 50% of the proctolin-degrading activity was isolated in a 30,000 g membrane fraction and was shown to be almost entirely due to aminopeptidase activity. The aminopeptidase had an apparent Km of 23 microM, a pH optimum of 7.0 and was inhibited by 1 mM-EDTA and amastatin [IC50 = 0.3 microM], but was relatively insensitive to bestatin, actinonin and puromycin. Phenylmethanesulphonyl fluoride (1 mM) and p-chloromercuriphenylsulphonic acid (1 mM) had no effect on this enzyme activity. Although the bulk of the Tyr-Leu hydrolytic activity was located in the 30,000 g supernatant, some weak activity was detected in a washed membrane preparation. This peptidase displayed a high affinity for proctolin (Km = 0.35 microM) and optimal activity at around pH 7.0. Synaptosome- and mitochondria-rich fractions were prepared from crude neural membranes. The aminopeptidase activity was concentrated in the synaptic-membrane preparation, whereas activity giving rise to Arg-Tyr was predominantly localized in the mitochondrial fraction. The subcellular localization of the membrane aminopeptidase is consistent with a possible physiological role for this enzyme in the inactivation of synaptically released proctolin.

scholarly journals Ecdysone 20-mono-oxygenase in the desert locust, Schistocerca gregaria

1984 ◽  
Vol 223 (3) ◽  
pp. 837-847 ◽  
Author(s):  
D R Greenwood ◽  
H H Rees
Keyword(s):  
Enzyme Activity ◽  
Schistocerca Gregaria ◽  
Specific Activity ◽  
Monochromatic Light ◽  
Malpighian Tubule ◽  
Malpighian Tubules ◽  
Lower Sensitivity ◽  
Marker Enzyme ◽  
Energy Dependent ◽  
Cytochrome P 450

The enzyme catalysing the hydroxylation of ecdysone to 20-hydroxyecdysone, ecdysone 20-mono-oxygenase (EC 1.14.99.22), was investigated in the Malpighian tubules of fifth-instar locusts, Schistocerca gregaria. Enzyme activity was optimal at 35 degrees C and pH 6.8-8.0. Under these conditions the mono-oxygenase exhibited an apparent Km for ecdysone of 7.1 × 10(-7) M, a maximal specific activity of 1.1 nmol/h per mg of protein and was competitively inhibited by 20-hydroxyecdysone with an apparent Ki of 6.3×10(-7) M. Enzyme activity was decreased in the presence of Ca2+, Mg2+, EDTA and non-ionic detergents. The Malpighian tubule ecdysone 20-mono-oxygenase was localized primarily in the subcellular fraction sedimenting at 7500 g and, on the basis of marker enzyme profiles, was assigned mainly to the mitochondria. NADPH was required for activity, although addition of NADH together with NADPH had a synergistic effect. NADP+-dependent isocitrate dehydrogenase (EC 1.1.1.42) and an energy-dependent NAD(P) transhydrogenase (EC 1.6.1.1.) appeared to be the major sources of reducing equivalents, with the contribution from the ‘malic enzyme’ (EC 1.1.1.40) being less important. The monooxygenase was characterized as a cytochrome P-450-containing mixed-function oxidase from the inhibition patterns with metyrapone, CO and cyanide; CO inhibition was reversible with monochromatic light at 450 nm. However, the ecdysone 20-mono-oxygenase shows much lower sensitivity to CO inhibition and to photodissociation of the CO-inhibited complex than do vertebrate cytochrome P-450-dependent hydroxylation systems. The concentration of cytochrome P-450 in the Malpighian tubule mitochondria was 30 pmol/mg of protein. The properties of the mono-oxygenase are discussed in relation to hydroxylation enzymes from other sources.

DNA Content and Synthesis in Several Tissues and Variation of Moulting Hormone-Level in Gryllus bimaculatus DEG (Ensifera, Insecta)

1983 ◽  
Vol 38 (1-2) ◽  
pp. 112-125 ◽  
Author(s):  
Franz Römer ◽  
Ilona Eisenbeis
Keyword(s):  
Dna Synthesis ◽  
Time Course ◽  
Fat Body ◽  
Larval Instar ◽  
Hormone Secretion ◽  
Postembryonic Development ◽  
Malpighian Tubules ◽  
Small Cells ◽  
Gryllus Bimaculatus ◽  
Moulting Hormone

The mode of growth of several tissues in Gryllus bimaculatus was investigated during postembryonic development by cytophotometric methods. In contrast to the situation in holo- metabolous insects, the tissues growing by endomitosis reach only moderate levels of polyploidy. In this case the growth of tissues is achieved by mitotic divisions of small cells with subsequent polyploidization. The time courses of DNA synthesis were measured within the 3rd and, for comparison, the 8th larval instar by incorporation of labelled thymidine followed by autoradiography. Hemocytes, cells of the regeneration crypts of the midgut, gonads and nervous tissue showed a continuous incorporation rate; by contrast, DNA synthesis in other tissues was confined to a given time within the moulting cycle. The changes in moulting hormone titre of the 3rd larval instar were investigated. The quantities of ecdysone and 20-OH-ecdysone were estimated by radioimmunoassay, and the hormones were identified by high pressure liquid chromatography (HPLC). The titre changes in time with at least 2 distinct maxima. The DNA synthesis periods are correlated with the hormone peaks, that of epidermis and tracheae with the first peak, and that of pylorus, ileum, rectum, Malpighian tubules and fat body with the second. DNA synthesis in prothoracic glands and oenocytes exhibits a time course that is the inverse of the hormone-secretion time course. The question whether moulting hormones have an influence on DNA synthesis is discussed.

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