Quinone Binding Sites of Membrane Proteins as Targets for Inhibitors

Quinones are a central component of most photosynthetic and respiratory electron transfer chains. The proteins that reduce and oxidise these quinones have quinone binding sites—Q sites—that are good targets for pesticides. This paper reviews the diversity of these sites, their possible structure, and the types of compounds that act upon them.     

The Validation of Pesticide Leaching Models

The validation of pesticide leaching models presents particular problems where the number of model predictions is far in excess of the observed data. Normally, however, there are more frequent field observations for other parameters (notably the site hydrology) than for pesticide concentrations in either water or soil. A five-stage validation procedure which takes advantage of the most frequently available observations and which tests each of the components of the model in a cumulative way, is thus advocated: Stage 1: Parameterisation of the model using only independently measured parameters. Stage 2: Hydrological validation: the validation of the predictions of water movement and water content of the soil. Stage 3: Solute movement validation: where field data are available for solutes other than pesticide, the model should first be validated for them, especially if they are more abundant than the pesticide observations. Conserved solutes such as chloride or bromide are preferred, although nitrate may be used for short periods. Stage 4: Pesticide fate in the soil: models should use parameters of pesticide fate derived from independent studies. Stage 5: Pesticide leaching: only in the last stage are the relatively small number of pesticide observations compared with the model predictions with respect to patterns and orders of magnitude of occurrence. With this scheme, the results of each stage are carried forward to the next, and confidence in the model is built with each stage. This is illustrated using the CRACK-P model and hydrological, nitrate and pesticide data from the Brimstone Farm Experiment Oxfordshire, UK.     

In-vitro Metabolism of a Novel Monocrotophos Derivative by Rat and Japanese Quail

NADPH-dependent inhibition of hepatic microsomal carboxylesterase by a derivative of monocrotophos (coded as RPR-5) was studied in rat and Japanese quail as a measure of monooxygenase-catalysed activation of RPR-5. There was NADPH-dependent inhibition of hepatic microsomal α-naphthyl acetate esterase (carboxylesterase) both in rat and quail, indicating monooxygenase-catalysed formation of an oxon that subsequently phosphorylated α-NaE. The pattern of in-vitro metabolism of ¹⁴C-labelled RPR-5 by 11000g supernatant (11-S), microsomes and 105000g supernatant (105-S) fractions of rat and quail livers suggested the involvement of microsomal monooxygenases and carboxylesterases. A radiolabelled metabolite (M2) was tentatively identified as an acid produced by carboxyl esterase attack. In rat, metabolism by microsomal and cytosolic (105-S) carboxylesterases appeared to predominate with relatively little oxidative metabolism. In quail, putative microsomal carboxylesterase hydrolysis of RPR-5 was much lower than in the rat with almost neglible hydrolysis by cytosolic fractions. Also, production of M₂ by quail microsomes was substantially reduced after addition of NADPH, suggesting inhibition of a carboxyl esterase by the oxon of RPR-5. Differences in this detoxification of RPR-5 between rat and quail may be an important factor in determining selective toxicity and the results underline the importance of relating metabolism to toxicity when selecting animal models for toxicity testing.     

Characterization and Inhibitor Studies of Chitinases from a Parasitic Blowfly (Lucilia cuprina), a Tick (Boophilus microplus), an Intestinal Nematode (Haemonchus contortus) and a Bean (Phaseolus vulgaris)

The molecular weight pattern and the stage-specific activities of chitinases from the blowfly Lucilia cuprina, the tick Boophilus microplus and the intestinal nematode Haemonchus contortus were examined. Chitinolytic enzymes could be detected in all parasite species tested, but the activity was different between the stages. Highest chitinolytic titers were found in blowfly pupae (83 kDa, 118 kDa), hatching larvae of ticks (58 kDa, 94 kDa) and nematode eggs (43 kDa). Leaves from ethylene-treated bean plants Phaseolus vulgaris expressed two basic Class I chitinases (Ia, Ib) of 34 kDa, differing in their amino acid sequences at residue 33 and 34 (Ia: glycine, proline; Ib: lysine, aspartic acid). Inhibitor studies with blowfly pupae revealed that allosamidin (IC₅₀=0·32 (±0·02) μM ) was by far the best inhibitor when compared with various amino sugar derivatives. This compound also inhibited chitinases from tick larvae (IC₅₀=0·69(±0·10) μM ) and nematode eggs (IC₅₀=0·048(±0·0045) μM ) specifically. Whereas Class Ia chitinase from bean leaves was inhibited only up to 18% by 10 μM allosamidin, it had an IC₅₀ of 1(±0·14) μM for the Ib type, which is the first plant chitinase described to be highly sensitive to allosamidin.     

Anthelmintic Actions of the Cyclic Depsipeptide PF1022A and its Electrophysiological Effects on Muscle Cells of Ascaris suum

The cyclic depsipeptide PF1022A, given orally to mice, showed very good anthelmintic activity against Heligmosomoides polygyrus and Heterakis spumosa at 50 mg kg⁻¹. In vitro, PF1022A was very active against Trichinella spiralis and had good activity against Nippostrongylus brasiliensis at 1 μg ml⁻¹. An 18-membered enniatin analogue, JES 1798, showed good activity only against N. brasiliensis at 10 μg ml⁻¹. The optical antipode of PF1022A had poor activity even at 100 μg ml⁻¹. The effects of PF1022A on the membrane potential and input conductance of somatic muscle of Ascaris suum were examined using a two-microelectrode current-clamp technique. PF1022A did not antagonize the effects of the selective nicotinic agonist levamisole. PF1022A and an analogue, JES 1798, but not the PF1022A antipode, produced a small time-dependent increase in input conductance associated with no potential change. The increase in input conductance did not occur in the Cl⁻-free bathing solution, suggesting that the increase in input conductance was mediated by Cl⁻ ions. The addition of high concentrations of Ca²⁺ to the preparation after the addition of PF1022A did not lead to production of Ca²⁺-activated Cl⁻ channels, suggesting that its mode of action was not that of a Ca²⁺ ionophore. The mechanism by which the cyclic depsipeptide might increase the Cl⁻ conductance is discussed.     

Using the RUSLE to identify factors controlling erosion rates of mine soils

Observable differences in particle size, smoothness and compaction between cap site (slope 2·8 per cent) and batter site (slope 20·7 per cent) surfaces on the waste rock dump at Ranger Uranium Mine were quantified in terms of revised universal soil loss equation (RUSLE) parameter values. Cap site surface material had a K_m (erodibility corrected for sediment density) of 0·030 and batter site surface material had a K_m of 0·0056. Using these K_m values (derived from particle size distributions), slope length and steepness (LS) factors of 0·36 for the cap site and 3·66 for the batter site, and a cover (C) factor of 0·45 for the cap site and 0·16 for the batter site, the RUSLE predicts an erosion rate from the cap site that is 1·9 times greater than erosion from the much steeper batter site. The RUSLE indicates that the finer particle size and blocky soil structure of the cap site (D₅₀ = 0·91 mm) compared with the looser granular structure of the batter site (D₅₀ = 1·74 mm) strongly influence erosion. The predictions are similar to observed soil losses from erosion plots on these sites under rainfall simulation events, for which the measured erosion rate from the cap site was approximately twice that from the batter site. For the RUSLE to predict the observed erosion rates, the support practice (P) factor for the cap site would have to be approximately 30 per cent greater than the P factor for the batter site. The higher cap site P factor probably results from smoothing and compaction caused by vehicle movement across the surface. Compaction is considered to have greatly reduced infiltration capacity, thus increasing the erodibility of the cap site. Vehicles probably also crushed the surface material at the cap site, creating the observed finer particle size distribution and further increasing the erodibility. Compaction, through its effects on erodibility (K_m) and surface roughness (P), is concluded to be the major cause of higher erosion from the cap site, even though the slope steepness is 10 times less. Parameterisation of the RUSLE quantifies the differences between sites and explains the unexpected erosion rates observed. The results highlight the need for careful management of rehabilitated sites to avoid increases in erosion which may arise from compaction by machinery.     

Spatiotemporal Distribution of Two Euschistus spp. Stink Bugs (Hemiptera: Pentatomidae) in Southeastern Farmscapes

Stink bugs (Hemiptera: Pentatomidae) are ubiquitous, cryptic, phytophagous pests that are found in many crops. In agroecosystems, individuals disperse from adjacent noncrop hosts and tend to aggregate or cluster within fields. In this study, we characterized the distribution of Euschistus servus (Say) and Euschistus tristigmus (Say) (Hemiptera: Pentatomidae) over 2 yr at three southeastern United States farmscapes. Stink bugs were captured in pheromone-baited traps, and Spatial Analysis by Distance Indices (SADIE) used to identify the location of significant aggregations by habitat type and season. Euschistus servus adults were more likely to be captured in pecan orchards, cotton, other crops, or unmanaged habitats than in woodland habitats. Significant aggregations of E. servus were detected in a variety of habitats including pecan, corn, cotton, peanut, and tobacco, as well as fallow and hay fields, pastures, and hedgerows. Fewer adult E. tristigmus were captured than E. servus adults, and E. tristigmus adults were typically trapped and aggregated in woodland habitats. The resulting data provide an important understanding regarding the seasonal movement and relative abundance levels of stink bug populations, which are critical to the development of integrated pest management strategies.     

Impact of Honey Bee Migratory Management on Pathogen Loads and Immune Gene Expression is Affected by Complex Interactions With Environment,Worker Life History,and Season

The effects of honey bee management, such as intensive migratory beekeeping, are part of the ongoing debate concerning causes of colony health problems. Even though comparisons of disease and pathogen loads among differently managed colonies indicate some effects, the direct impact of migratory practices on honey bee pathogens is poorly understood. To test long- and short-term impacts of managed migration on pathogen loads and immunity, experimental honey bee colonies were maintained with or without migratory movement. Individuals that experienced migration as juveniles (e.g., larval and pupal development), as adults, or both were compared to control colonies that remained stationary and therefore did not experience migratory relocation. Samples at different ages and life-history stages (hive bees or foragers), taken at the beginning and end of the active season, were analyzed for pathogen loads and physiological markers of health. Bees exposed to migratory management during adulthood had increased levels of the AKI virus complex (Acute bee paralysis, Kashmir bee, and Israeli acute bee paralysis viruses) and decreased levels of antiviral gene expression (dicer-like). However, those in stationary management as adults had elevated gut parasites (i.e. trypanosomes). Effects of environment during juvenile development were more complex and interacted with life-history stage and season. Age at collection, life-history stage, and season all influenced numerous factors from viral load to immune gene expression. Although the factors that we examined are not independent, the results illuminate potential factors in both migratory and nonmigratory beekeeping that are likely to contribute to colony stress, and also indicate potential mitigation measures.     

Effects of Cocoa-Derived Polyphenols on Cognitive Function in Humans. Systematic Review and Analysis of Methodological Aspects

Plant Foods for Human Nutrition - The effects of cocoa-derived polyphenols on cognitive functions have been analyzed through numerous studies using different interventions (doses, vehicles, time...