Trophic Shifts of a Generalist Consumer in Response to Resource Pulses

Trophic shifts of generalist consumers can have broad food-web and biodiversity consequences through altered trophic flows and vertical diversity. Previous studies have used trophic shifts as indicators of food-web responses to perturbations, such as species invasion, and spatial or temporal subsidies. Resource pulses, as a form of temporal subsidies, have been found to be quite common among various ecosystems, affecting organisms at multiple trophic levels. Although diet switching of generalist consumers in response to resource pulses is well documented, few studies have examined if the switch involves trophic shifts, and if so, the directions and magnitudes of the shifts. In this study, we used stable carbon and nitrogen isotopes with a Bayesian multi-source mixing model to estimate proportional contributions of three trophic groups (i.e. producer, consumer, and fungus-detritivore) to the diets of the White-footed mouse (Peromyscus leucopus) receiving an artificial seed pulse or a naturally-occurring cicadas pulse. Our results demonstrated that resource pulses can drive trophic shifts in the mice. Specifically, the producer contribution to the mouse diets was increased by 32% with the seed pulse at both sites examined. The consumer contribution to the mouse diets was also increased by 29% with the cicadas pulse in one of the two grids examined. However, the pattern was reversed in the second grid, with a 13% decrease in the consumer contribution with the cicadas pulse. These findings suggest that generalist consumers may play different functional roles in food webs under perturbations of resource pulses. This study provides one of the few highly quantitative descriptions on dietary and trophic shifts of a key consumer in forest food webs, which may help future studies to form specific predictions on changes in trophic interactions following resource pulses

Reaction of clavams with elastase reveals a general method for inhibiting 'serine' enzymes

Ester derivatives of clavulanic acid acylate Ser-195 of the serine protease porcine pancreatic elastase to form stable malonyl semi-aldehyde derivatives, analogous to those formed in the inhibition of β-lactamases by clavulanic acid itself. Formation of such derivatives maybe a general way of inhibiting 'serine' enzymes. (C) 2000 Elsevier Science Ltd

Tetrahydrofuran amino acids: Secondary structure in tetrameric and octameric carbopeptoids derived from a D-allo 5-(aminomethyl)tetrahydrofuran-2-carboxylic acid

The synthesis of a D-allo-5-(azidomethyl)tetrahydrofuran-2-carboxylate as an amino acid precursor (in which the carboxylic acid is cis to the azidomethyl substituent and trans to the diol moiety) is reported from D-ribose. The oligomerisation of this monomer to dimeric, tetrameric and octameric carbopeptoids is described. NMR studies into the solution structures of cyclohexylidene-protected oligomers and of a deprotected tetramer with eight free hydroxy groups are described. © The Royal Society of Chemistry 2000

An octameric carbopeptoid; secondary structure in octameric and tetrameric 5-aminomethyl-tetrahydrofuran-2-carboxylates

The efficient synthesis of an octameric furanose carbopeptoid, readily purified by chromatography in ethyl acetate:hexane (2:1), is reported. Extensive NMR studies suggest that two tetrameric 5- aminomethyltetrahydrofuran-2-carboxylates are prone to adopt solution conformations reminiscent of a repeating β-turn, a third tetramer and the corresponding octamer may tend towards a left-handed α-helix

An approach to insulated molecular wires: synthesis of water-soluble conjugated rotaxanes

Hydrophobic self-assembly has been used to direct the synthesis of conjugated [2] and [3]rotaxanes (20 and 21) in aqueous solution, by Glaser coupling a water-soluble alkyne 3 in the presence of a cyclophane 6. No rotaxanes were formed when cyclodextrins were used instead of the cyclophane. NMR and electrospray mass spectrometry were used to probe the binding properties of the stopper unit 3. NMR ring current shifts and NOEs show that the cyclophane 6 binds mainly to the terminal phenylene unit of 3. In solution cyclodextrins bind less strongly than the cyclophane, whereas in the gas-phase cyclodextrins bind more strongly. The water-soluble rotaxanes are fully characterised by electrospray mass spectrometry, NMR and UV-VIS emission/absorption. Both rotaxanes tend to fragment, by unthreading and by dumbbell-cleavage, during electrospray ionisation, particularly at high cone voltages. The insulation of the conjugated dumbbell inside the [3]rotaxane results in increased fluorescence efficiency. Time-resolved fluorescence measurements show that these rotaxanes decompose during photolysis to give products with longer fluorescence lifetimes; the rate of this photodecomposition is slower for the [3]rotaxane than for the naked dumbbell. The extension of this synthetic approach to larger polyrotaxanes was explored by coupling alkyne 3 and diethynylbenzene 2 in the presence of cyclophane 6; this gives some longer [2] and [3]rotaxanes but higher polyrotaxanes are not formed

Mechanistic insights into the inhibition of serine proteases by monocyclic lactams.

Although originally discovered as inhibitors of pencillin-binding proteins, beta-lactams have more recently found utility as serine protease inhibitors. Indeed through their ability to react irreversibly with nucleophilic serine residues they have proved extraordinarily successful as enzyme inhibitors. Consequently there has been much speculation as to the reason for the general effectiveness of beta-lactams as antibacterials or inhibitors of hydrolytic enzymes. The interaction of analogous beta- and gamma-lactams with a serine protease was investigated. Three series of gamma-lactams based upon monocyclic beta-lactam inhibitors of elastase [Firestone, R. A. et al. (1990) Tetrahedron 46, 2255-2262.] but with an extra methylene group inserted between three of the bonds in the ring were synthesized. Their interaction with porcine pancreatic elastase and their efficacy as inhibitors were evaluated through the use of kinetic, NMR, mass spectrometric, and X-ray crystallographic analyses. The first series, with the methylene group inserted between C-3 and C-4 of the beta-lactam template, were readily hydrolyzed but were inactive or very weakly active as inhibitors. The second series, with the methylene group between C-4 and the nitrogen of the beta-lactam template, were inhibitory and reacted reversibly with PPE to form acyl-enzyme complexes, which were stable with respect to hydrolysis. The third series, with the methylene group inserted between C-2 and C-3, were not hydrolyzed and were not inhibitors consistent with lack of binding to PPE. Comparison of the crystal structure of the acyl-enzyme complex formed between PPE and a second series gamma-lactam and that formed between PPE and a peptide [Wilmouth, R. C., et al. (1997) Nat. Struct. Biol. 4, 456-462.] reveals why the complexes formed with this series were resistant to hydrolysis and suggests ways in which stable acyl-enzyme complexes might be obtained from monocyclic gamma-lactam-based inhibitors