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Biomedical subjects

W S Bowers

Publications and source records attributed to W S Bowers.

At least 19 recordsLinked to original sources
PubMed2001

Defensive chemistry of an aposematic bug, Pachycoris stallii Uhler and volatile compounds of its host plant Croton californicus Muell.-Arg.

Volatile components of Pachycoris stallii scent gland secretions and the bug's host plant, Croton californicus, were identified by gas chromatography and mass spectroscopy. The predominant compounds isolated from C. californicus fruit and leaves were beta-myrcene and beta-caryophyllene. Metathoracic gland secretions of P. stallii contained mostly (E)-2-hexenal, (E)-4-oxo-2-hexenal, (E)-2-hexenyl acetate, and n-tridecane. In males, n-tridecane was present throughout the metathoracic gland, but in females this compound was found only in the median reservoir/accessory gland. (E)-2-Hexenal was present throughout the gland of female bugs, but in males was primarily present in the median reservoir/accessory gland. (E)-4-Oxo-2-hexenal and n-dodecane were isolated from the median reservoir/accessory gland of male and female bugs. Metathoracic glands were sexually monomorphic. Data from chemical analyses and anatomical observations suggest that dorsal abdominal glands of adults were apparently obsolescent. In nymphs, dorsal abdominal glands produced (E)-2-hexenal, (E )-4-oxo-2-hexenal, n-dodecane, n-tridecane, and tetradecanal. The proportion of the predominant constituent, (E)-4-oxo-2-hexenal, decreased from 72% in the first instar to 47% in the fourth instar. Proportions of tetradecanal and n-tridecane were greater in the fourth instar than in the first instar. Observations of dissected glands indicated that median and posterior dorsal abdominal glands of all nymphal instars were more developed than anterior dorsal abdominal glands. Scanning electron micrography revealed the presence of polygonal microsculpturing on the integument surrounding the ostioles of metathoracic and dorsal abdominal glands. Chemical, anatomical, and behavioral data indicated that P. stallii has a chemical defense system based on short-chain carbonyl compounds and that this system is directed against arthropods. The abundance of arthropod natural enemies apparently has forced P. stallii to maintain this defense system despite feeding on a toxic host plant.

Acetates↗
PubMed1998

A cytochrome P450 terpenoid hydroxylase linked to the suppression of insect juvenile hormone synthesis.

A cDNA encoding a cytochrome P450 enzyme was isolated from a cDNA library of the corpora allata (CA) from reproductively active Diploptera punctata cockroaches. This P450 from the endocrine glands that produce the insect juvenile hormone (JH) is most closely related to P450 proteins of family 4 and was named CYP4C7. The CYP4C7 gene is expressed selectively in the CA; its message could not be detected in the fat body, corpora cardiaca, or brain, but trace levels of expression were found in the midgut and caeca. The levels of CYP4C7 mRNA in the CA, measured by ribonuclease protection assays, were linked to the activity cycle of the glands. In adult females, CYP4C7 expression increased immediately after the peak of JH synthesis, reaching a maximum on day 7, just before oviposition. mRNA levels then declined after oviposition and during pregnancy. The CYP4C7 protein was produced in Escherichia coli as a C-terminal His-tagged recombinant protein. In a reconstituted system with insect NADPH cytochrome P450 reductase, cytochrome b5, and NADPH, the purified CYP4C7 metabolized (2E,6E)-farnesol to a more polar product that was identified by GC-MS and by NMR as (10E)-12-hydroxyfarnesol. CYP4C7 converted JH III to 12-trans-hydroxy JH III and metabolized other JH-like sesquiterpenoids as well. This omega-hydroxylation of sesquiterpenoids appears to be a metabolic pathway in the corpora allata that may play a role in the suppression of JH biosynthesis at the end of the gonotrophic cycle.

Amino Acid Sequence↗
PubMed1997

Substrate specificity for the epoxidation of terpenoids and active site topology of house fly cytochrome P450 6A1.

Heterologous expression in Escherichia coli, purification, and reconstitution of house fly P450 6A1 and NADPH-cytochrome P450 reductase were used to study the metabolism of terpenoids. In addition to the epoxidation of cyclodiene insecticides demonstrated previously [Andersen et al. (1994) Biochemistry 33, 2171-2177], this cytochrome P450 was shown to epoxidize a variety of terpenoids such as farnesyl, geranyl, and neryl methyl esters, juvenile hormones I and III, and farnesal but not farnesol or farnesoic acid. P450 6A1 reconstituted with NADPH-cytochrome P450 reductase and phosphatidylcholine did not metabolize alpha-pinene, limonene, of the insect growth regulators hydroprene and methoprene. The four geometric isomers of methyl farnesoate were metabolized predominantly to the 10,11-epoxides, but also the 6,7-epoxides and to the diepoxides. The 10,11-epoxide of methyl (2E,6E)-farnesoate was produced in a 3:1 ratio of the (10S) and (10R) enantiomers. Monoepoxides of methyl farnesoate were metabolized efficiently to the diepoxides. Methyl farnesoate epoxidation was strongly inhibited by a bulky substituted imidazole. The active site topology of P450 6A1 was studied by the reaction of the enzyme with phenyldiazene to form a phenyl-iron complex. Ferricyanide-induced in situ migration of the phenyl group showed formation of the N-phenylprotopor-phyrinporphyrin IX adducts in a 17:25:33:24 ratio of the NB:NA:NC:ND isomers. These experiments suggest that metabolism of xenobiotics by this P450, constitutively overexpressed in insecticide-resistant strains of the house fly, is not severely limited by stereochemically constrained access to the active site.

Animals↗
PubMed1988

Insect lipid transfer particle catalyzes diacylglycerol exchange between high-density and very-high-density lipoproteins.

Facilitated diacylglycerol exchange between Manduca sexta [3H]diacylglycerol-labeled high-density lipophorin and Heliothis zea very-high-density chromolipoprotein was studied. M. sexta lipid transfer particle was employed in assays which measured exchange of [3H]diacylglycerol. Following incubations with lipid transfer particle, donor and acceptor lipoproteins were reisolated by density-gradient ultracentrifugation to determine facilitated exchange. The reaction was limited to diacylglycerol exchange, while donor or acceptor particle apoprotein exchange did not occur. Lipid analysis of donor and acceptor lipoproteins after the lipid-exchange reaction revealed that the labeled diacylglycerol remained unchanged. Lipid transfer particle-catalyzed diacylglycerol exchange was linear up to 0.3 micrograms lipid transfer particle protein in a standard assay and exchange occurred at a rate of 2.5 micrograms diacylglycerol min-1.micrograms-1 lipid transfer particle protein. The assay method was used to show that the hemolymph concentration of lipid transfer particle increased during development.

Animals↗
PubMed1987

Purification of very high density lipoproteins by differential density gradient ultracentrifugation.

Differential density gradient ultracentrifugation procedures, utilizing a vertical rotor, were developed for the preparative purification of very high density lipoproteins (VHDL, density greater than 1.21 g/ml). The VHDLs of several insect species were purified as follows. An initial density gradient ultracentrifugation step removed lipoproteins of lower density from the VHDL-fraction, which partially separated from the nonlipoproteins present in the infranatant. A complete separation was achieved by a second centrifugation step employing a modified gradient system. The use of a vertical rotor and specially designed discontinuous gradients allows a relatively fast, efficient, and economical isolation of the class of very high density lipoproteins. Similar gradient systems should be useful for the detection and purification of VHDLs from other sources.

Animals↗
PubMed1986

A larval specific lipoprotein: purification and characterization of a blue chromoprotein from Heliothis zea.

The green color of the hemolymph of last instar larvae of the corn earworm, Heliothis zea (Boddie), is caused by the appearance of a blue chromoprotein. This protein (Mr approximately 560,000) is composed of 4 subunits (Mr approximately 150,000). It contains 8.4% lipid and has an equilibrium density of 1.26 g/ml. This protein is absent during all early larval stages, in pupae and in adult animals, but is a major hemolymph protein in 5th instar larvae. Although its physiological function remains unclear, this blue chromoprotein represents the first member of a new class of larval-specific insect lipoproteins.

Animals↗
PubMed1984

Insect-plant interactions: endocrine defences.

It is the inevitable consequence of evolution that competitive species living together in a restricted space must try to exclude each other. Plants and insects are prime examples of this eternal competition, and although neither of these is in danger of extinction, their mutual defensive strategies are of compelling interest to the human race. Plant defences based on the insecticidal activity of certain of their secondary chemicals are readily apparent. Only through research into the fundamentals of insect physiology and biochemistry are more subtle defensive mechanisms revealed, linked to the disruption of the insect endocrine system. A diverse number of chemical structures are found in plants, which interfere with hormone-mediated processes in insects. Examples include: mimics of the insect's juvenile hormones such as juvabione from the balsam fir and the juvocimenes from sweet basil, which lethally disrupt insect development, and the precocenes found in Ageratum species, which act as anti-juvenile hormonal agents. The latter appear to serve as 'suicide substrates', undergoing activation into cytotoxins when acted on by specialized enzymes resident in the insect endocrine gland (corpus allatum) that is responsible for juvenile hormone biosynthesis and secretion. Consideration of these plant defensive strategies, which have been reached through aeons of evolutionary experimentation, may assist the human race in its defences against its principal competitors for food, fibre and health.

Adaptation, Biological↗
PubMed1982

The effects of precocene II on reproduction and development of triatomine bugs (Reduviidae: Triatominae).

Precocene II is a botanically derived chemical that inhibits the production of juvenile hormone (JH) in insects. The effects of this anti-JH compound on molting and growth by Rhodnius prolixus and Triatoma dimidiata and reproduction in R. prolixus were tested and the efficacy of precocene II as a fumigant was assessed. Precocene II induced precocious metamorphosis in both species when applied by either contact exposure or fumigation, and this effect could be prevented by juvenile hormone replacement therapy. The dosage effective in inducing precocious metamorphosis in T. dimidiata was similar to the EC50 previously reported for R. prolixus. The morphology of precocious adultoid T. dimidiata of different instars was similar to Rhodnius adultoids of corresponding instars. However, T. dimidiata was more sensitive than Rhodnius to the molt-inhibiting effects of precocene II. Rhodnius nymphs were fully susceptible to the anti-JH action of precocene when exposed for 24 hours one week before feeding. Precocene II was highly toxic to adult female Rhodnius and treatment of newly emerged females prevented oogenesis.

Animals↗
PubMed1976

Discovery of insect anti-juvenile hormones in plants.?2U.

Two simple chromenes with anti-JH activity have been isolated and identified from the bedding plant Ageratum houstoianum. By contact and fumigation these compounds induce precocious metamorphosis and sterilization in several hemipteran species of insects. Certain holometabolous species are sterilized, forced into diapause, or both. Each of these biological actions is equivalent to removal of the corpora allata, which produce the JH's, and is reversible by treatment with exogenous JH. Thus, the action of these compounds is to stop the production or depress the titer of the JH's. To our knowledge, this is the first discovery of anti-JH, and we hope it will guide the way to the emergence of a fourth generation of safe and insect-specific pesticides.

Female↗
PubMed1976

Ant-aphid association: role of aphid alarm pheromone.

When attacked by predators, aphids secrete alarm pheromones that cause nearby aphids to disperse. Ant-associated (myrmecophilous) aphid species disperse less readily than nonmyrmecophilous species. The ant Formica subsericea responds to aphid alarm pheromone in a way that is beneficial to the aphid. These findings support our hypothesis that myrmecophilous aphids depend more on ants for protection from predators than on their own dispersive powers.

Animals↗