Reaction mechanism of surfactant‐sensitized chemiluminescence of bis(2,4,6‐trichlorophyenyl) oxalate and hydrogen peroxide induced by gold nanoparticles

The chemiluminescence (CL) of bis(2,4,6‐trichlorophyenyl) oxalate with hydrogen peroxide in the present of cationic surfactant and gold nanoparticles was studied. The CL emission was obviously enhanced in the presence of surfactant at a suitable concentration, with a synergetic catalysis effect exhibited. Different sizes of gold nanoparticles (15 and 50 nm) showed different effects on CL intensity. Mechanisms of the CL reaction and sensitization effect are discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

Pre‐copulation intervals,copulation frequencies,and initial progeny sex ratios in two biotypes of whitefly,Bemisia tabaci

The whitefly Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) is a species complex, and its systematic classification requires controlled crossing experiments among its genetic groups. Accurate information on pre‐copulation intervals, copulation frequencies, and initial frequency of egg fertilization of newly emerged adults is critical for designing procedures for collecting the virgin adults necessary for these experiments. In the literature, considerable variation is reported between B. tabaci populations, with respect to the length of the pre‐copulation interval and the initial frequency of egg fertilization. Here, we used a video‐recording method to observe continuously the copulation behaviour of the Mediterranean/Asia Minor/Africa (B biotype) and the Asia II (ZHJ1 biotype) groups of B. tabaci. We also recorded the initial frequency of egg fertilization, as determined by the sex of the progeny. When adults were caged in female–male pairs on leaves of cotton plants, the earliest copulation events occurred 2–6 h after emergence; at 12 h after emergence 56–84% of the females had copulated at least once, and nearly all (92–100%) had copulated at least once by 36 h after emergence. Both females and males copulated repeatedly. Approximately 80 and 20% of copulation events occurred during the photophase and scotophase, respectively. By 72 h post‐emergence, the females of the B and ZHJ1 biotypes had copulated on average 6.1 and 3.9 times, respectively. When adults were caged in groups on plants 1–13 h after emergence, 30–35% of the eggs deposited during this period were fertilized, and approximately 90% of females were fertilized by the end of the 13 h. Although timing of copulation differed in detail between the two genetic groups, the results demonstrate that B. tabaci adults can start to copulate as early as 2–6 h post‐emergence and the majority of females can become fertilized on the day that they emerge.     

A single amino acid substitution deregulates a bacterial lactate dehydrogenase and stabilizes its tetrameric structure

We have engineered a variant of the lactate dehydrogenase enzyme from Bacillus stearothermophilus in which arginine-173 at the proposed regulatory site has been replaced by glutamine. Like the wild-type enzyme, this mutant undergoes a reversible, protein-concentration-dependent subunit assembly, from dimer to tetramer. However, the mutant tetramer is much more stable (by a factor of 400) than the wild type and is destabilized rather than stabilized by binding the allosteric regulator, fructose 1,6-biphosphate (Fru-1,6-P2). The mutation has not significantly changed the catalytic properties of the dimer (Kd NADH, Km pyruvate, Ki oxamate and kcat), but has weakened the binding of Fru-1,6-P2 to both the dimeric and tetrameric forms of the enzyme and has almost abolished any stimulatory effect. We conclude that the Arg-173 residue in the wild-type enzyme is directly involved in the binding of Fru-1,6-P2, is important for allosteric communication with the active site, and, in part, regulates the state of quaternary structure through a charge-repulsion mechanism.     

Rational construction of a 2-hydroxyacid dehydrogenase with new substrate specificity

Using site-directed mutagenesis on the lactate dehydrogenase gene from Bacillus stearothermophilus, three amino acid substitutions have been made at sites in the enzyme which we suggest in part determine specificity toward different hydroxyacids (R-CHOH-COOH). To change the preferred substrates from the pyruvate/lactate pair (R = -CH3) to the oxaloacetate/malate pair (R = -CH2-COO-), the volume of the active site was increased (thr 246----gly), an acid was neutralized (asp-197----asn) and a base was introduced (gln-102 - greater than arg). The wild type enzyme has a catalytic specificity for pyruvate over oxaloacetate of 1000 whereas the triple mutant has a specificity for oxaloacetate over pyruvate of 500. Despite the severity and extent of these active site alterations, the malate dehydrogenase so produced retains a reasonably fast catalytic rate constant (20 s-1 for oxaloacetate reduction) and is still allosterically controlled by fructose-1,6-bisphosphate.     

Effect of biological toxins on gap-junctionai intercellular communication in Chinese hamster V79 cells

Since chemical modulation of gap junctional intercellular communication has been implicated in several toxicological endpoints, a study to examine the ability of several biological toxins to inhibit this process was undertaken. Eight biological toxins were tested for their ability to inhibit metabolic cooperation, a measure of gap-junctional intercellular communication, in the Chinese V79 cell system. Aplysiatoxin, anhydrodebromoaplysiatoxin and debromoaplysiatoxin showed the strongest ability to inhibit metabolic cooperation while T2-toxin and vomitoxin inhibited metabolic cooperation to a lesser degree. Afatoxin B₁, afatoxin B₂ and palytoxin were inactive in the Chinese V79 system. Palytoxin, which was extremely cytotoxic, might act as a tumor promoter if it induces compensatory hyperplasia in vivo.Abbreviations 6-TG 6-thioguanine - TPA 12-0-tetradecanoylphorbol-13-acetate     

The fine structure of the newly discovered propodial ganglia of the veliger larva of the nudibranch Onchidoris bilamellata

Summary Two pairs of ganglia are found in the propodial region of the veliger of Onchidoris bilamellata: the anterolateral pair is located at the foremost corners of the propodium, and the frontal pair is located beside the propodial midline. Both sets of ganglia are positioned below the epidermis, and they are joined to the cerebral ganglia by large, common connectives. Each ganglion possesses sensory cells, nerve cells and sheath cells, and the frontal pair contains a complement of secretory cells. Externally, the propodial ganglia are manifested as sensory fields. The fields of the anterolateral pair are elliptical in shape, and each appears as a band of cilia bordering an unciliated zone. The region devoid of cilia is composed of ordinary epidermal cells, whereas the ciliated portion is comprised of dendritic endings originating from cells in the ganglion. Dendrites arise from one type of sensory cell and pass through the epidermis in bundles. Each dendrite terminates as a single cilium at the epidermal surface. Sensory fields of the frontal ganglia are key-shaped and oppose one another on the anterior end of the foot. Each field appears as a flat, circular, unciliated region which extends into a ciliated groove that runs dorsally toward the mouth. The groove contains the terminals of secretory cells, ciliated sensory cells, and the cell bodies of nonciliated sensory cells. The nonciliated sensory cells, characterized by a microvillous apex, are the dominant cells in the flattened circular zone. The space between the frontal ganglia and the epidermis is bridged by bundles of processes which are similar to those of the anterolateral ganglia. However, these tracts contain collections of the apical processes of secretory cells, the dendrites of ciliated sensory cells, and the axons of nonciliated sensory cells. Morphological and behavioral evidence indicates that the propodial ganglia serve a chemosensory function during settlement and metamorphosis.     

Effect of a melatonin implant on the circadian variation of plasma prolactin and rectal temperature in newborn sheep.

Plasma prolactin and rectal temperature show a circadian rhythm in newborn sheep raised under continuous light. Melatonin lowers the concentration of plasma prolactin but it is not known if it affects its circadian rhythm. To detect whether melatonin acts on the circadian system we studied the effect of a subcutaneous melatonin implant in the circadian rhythms of prolactin and rectal temperature in newborn lambs raised under continuous light. We placed catheters in the pedal artery and vein in 9 newborn lambs (2-5 days of age). A subcutaneous melatonin implant was placed in 4 of the lambs at 9-12 days of age. Blood samples and rectal temperature measurements were obtained hourly for a period of 24 h, 11-15 days after the implant, at 20-27 days of age. To avoid interferences of heparin in our melatonin assay, serum melatonin concentration was measured before and during the implant in three additional newborns. Prolactin and melatonin were measured by RIA. Melatonin concentrations were 52.8 +/- 45.9 pg/ml (day) and 315.5 +/- 77.0 pg/ml (night) before treatment (SEM, P less than 0.001), and increased to 594.1 +/- 54.5 pg/ml after placing the implant (there was no difference in melatonin concentration between day and night during the time that the implant was in place). Melatonin had no effect on rectal temperature or its rhythm, but decreased basal plasma prolactin concentration (control: 97.5 +/- 11.3 ng/ml; treated: 25.1 +/- 2.4 ng/ml, P less than 0.001) and abolished the prolactin circadian rhythm, (Cosinor analysis): control: log prolactin (ng/ml) = 1.8 + 0.26 cos 15 (t - 11.16), p = 0.05; treated: log prolactin (ng/ml) = 1.2 + 0.14 cos 15 (t - 9.43), P = 0.36.     

Changes in soil microflora associated with control of Sclerotium Rolfsii by Furfuraldehyde

The efficacy of 2‐furfuraldehyde for control of Sclerotium rolfsii was studied in laboratory and greenhouse experiments. Mycelial growth of the fungus was reduced proportionally with concentrations of 0.1–0.5 ml furfuraldehyde l^‐1 agar medium, and viability of sclerotia diminished on exposure to 2‐furfuraldehyde vapours. Detectable populations of bacteria and fungi, including Trichoderma spp., were reduced significantly (9=0.05) when furfuraldehyde was added to the agar used for soil dilution plates of untreated soil. Repeated treatments of natural soil with the fumigant significantly increased populations of Trichoderma spp. and bacteria, but diminished numbers of actinomycetes. Increasing dosages applied to soil artificially infested with S. rolfsii caused a reduction of disease on lentil, Lens culinaris. Results indicate that the compound, when applied to field soil, changes the composition of soil microflora and has potential for integrated control of S. rolfsii.