The physicochemical transmission of two components of a multiple chemical signal in the African weaver ant, (Oecophylla longinoda)

The behavioural thresholds of the two principal components of the mandibular gland secretion in major workers of the weaver ant Oecophylla longinoda, hexanal and 1-hexanol, were found to be 1.99×10¹⁰ and 3.35×10¹¹ molecules cm^?3 respectively. The mandibular gland contains an average of 2.896×10¹⁵ molecules of hexanal, and 1.274×10¹⁶ molecules of 1-hexanol. From these measurements, molecular diffusion theory predicts behavioural active spaces for 1-hexanol (an attractant) which agree with those observed in response to the whole secretion, but there is no such agreemnet for haxanal (a releaser of behaviour with no directionial compnent). The effect of microturbulence on the transmission of releaser and chemotactic stimuli is discussed.     

Effects of simulated trawling on sablefish and walleye pollock: the role of light intensity, net velocity and towing duration

Laboratory apparatus which simulated capture of fish in the cod-end of a towed trawl was used to induce post-capture stress as measured by alterations in behavioural, physiological and mortality indices in juvenile walleye pollock Theragra chalcogramma and juvenile and adult sablefish Anoplopoma fimbria. Differences in resistance to net entrainment varied between species with the severity of stress and the potential for recovery depending on light intensity, net velocity and towing duration. At a light intensity which simulated daylight at depth in clear ocean water (0.5 μmol photons m^?2 s^?1), walleye pollock juveniles were able to maintain swimming in nets towed at 0.65 m s^?1 for 3h with no discernible effects on behaviour or mortality. However, when net velocity was increased to >0.75m s^?1 or light intensity was decreased to <0.002 μmol photons m^?2 s^?1, fish became entrained in the meshes of the net and exhibited significant alterations in feeding behaviour, predator evasion and increases in plasma cortisol concentrations. Marked increases in stress-induced mortality also occurred, in some cases after a delay of 6 days and eventually reaching 100%. In comparison with walleye pollock, sablefish juveniles became entrained in the meshes of the net at higher velocities (>0.92m s^?1) or lower light intensities (<0.0004 μmol photons m^?2 s^?1) and were much more resistant to post-capture stress. Towing of net-entrained fish for 15 min caused no detectable changes in feeding and cortisol and for 2 h, no changes in feeding although mortality increased from 0% for 15-min tows to 19% for 2-h tows. Towing for 4 h caused significant alterations in feeding and cortisol with feeding recovering to control levels by 6 days and cortisol by 3 days; mortality was 25%. When adult sablefish were towed for 4 h followed by 15-min exposure to air, feeding was inhibited 6 days after towing, but recovered within 30 days with no mortality observed after 30 days. The results demonstrate the value of using laboratory-based behavioural and biochemical indices to identify factors that may potentially affect post-capture survival among different species of fish.     

Direct observation of swimming behaviour in a shallow-water scavenging amphipod Scopelocheirus onagawae in relation to chemoreceptive foraging

Direct observations on foraging behaviour of scavenging lysianassid amphipods have been limited, and no previous study has examined the effect of food odour quantitatively on the behaviour. The present study recorded the swimming behaviour of the amphipod Scopelocheirus onagawae using videographic techniques before and after the introduction of food odour (amino acid solution). S. onagawae showed consistent nocturnal activity swimming at a high speed (16.8 cm s^− 1) with an approximately straight trajectory in various directions before and after the introduction of odour in which the amino acid concentration was below the behavioural threshold concentration for this species (1.0 × 10^− 7 mol l^− 1). High speed multidirectional linear swimming is thought to be advantageous for these amphipods, enabling them to survey across a broad area. After the first encounter with the odour plume above the behavioural threshold concentration, the amphipods slowed down their swimming speed (ca. 9.7 cm s^− 1) with a short time-lag (ca. 0.42 s), and thereafter they frequently turned so that they remained within the odour plume. Once moved out of the odour plume, the amphipods quickly returned to the plume with a shorter response time (ca. 0.1 s) than that in the first detection of the odour plume, suggesting that the sensory adaptation is involved with the tracking of the odour. Our study demonstrated that chemoreception is a major factor causing behavioural change in scavenging amphipods at the edge of the odour plume.     

Bioaccessibility-Based Risk Assessment of PAHs in Soils from Sites of Different Anthropogenic Activities in Lagos,Nigeria Using the Fed Organic Estimation Human Simulation Test Method

The aim of this study was to carry out a bioaccessibility-based risk assessment of polycyclic aromatic hydrocarbons (PAHs) in soils from sites of different anthropogenic activities in Lagos, Nigeria. Using an in vitro gastrointestinal model—Fed Organic Estimation Human Simulation Test method (FOREShT), the concentration of bioaccessible 16 priority US Environmental Protection Agency (USEPA) PAHs in soils were determined. Total concentration of 16 priority USEPA PAHs was also determined. The concentration range was 702–253,922 ng g^?1 and 92–760 ng g^?1 for total and bioaccessible PAHs, respectively. For persons involved with activities at these sites no health risks were observed, based on bioaccessibility values of PAHs. Mean daily intake of PAHs from these soils were below the oral mean daily intake threshold for PAHs in food. Also, overall estimated theoretical cancer risk (2.5 × 10^?09, 6.5 × 10^?07, 5.5 × 10^?10, 2.7 × 10^?09, 6.5 × 10^?10, 9.5 × 10^?10, 2.0 × 10^?09, and 4.1 × 10^?07 for the eight sites based on their bioaccessible concentration) for exposure to PAHs in surface soils were below the health guidelines for extreme (1 × 10^?04) and normal (1 × 10^?06) exposures.     

Type-3 functional response in limnetic suspension-feeders,as demonstrated by in situ grazing rates

Field-measured grazing rates (ml/animal/d) of cladocerans (mostly daphniids) and diaptomids were assembled from various published studies and plotted as a function of corresponding phytoplankton concentration (μg l⁻¹ f.w.). Filtering rates of both zooplankton groups initially increased with seston concentration until maximal grazing rates were observed at approximately 4 × 10² and 1 × 10² μg l⁻¹ for cladocerans and copepods, respectively; at higher algal concentrations, filtering rates of both declined as a function of food concentration. The shape of these curves are most consistent with Holling's (1966) Type 3 functional response. We found little support for the Type 3 functional response in published laboratory studies of Daphnia; most investigators report either a Type 1 or Type 2 response. The one study in which the Type 3 response was observed involved experiments where animals were acclimated at low food concentrations for 24 h, whereas those studies associated with response Types 1 or 2 had acclimation periods of only 1 to 3 h. We therefore assembled relevant data from the literature to examine the effect of acclimation period on the feeding rates of Daphnia at low food concentrations. In the absence of any acclimation, animals filtered at extremely low rates. After 2 h of acclimation, however, filtering rates increased 4 to 5-fold but declined again with longer durations; after > 70 h of pre-conditioning, filtering rates were almost as low as they had been with no acclimation. We also found little support for the Type 3 functional response in published studies of copepods. The only study associated with a Type 3 response involved a marine copepod that had been subjected to a starvation period of 48 h; however, an analysis of the effects of acclimation period did not yield conclusive evidence that filtering rates of freshwater copepods (Diaptomus and Eudiaptomus) decrease significantly with acclimation duration. The low filtering rates associated with long acclimation periods in laboratory experiments appears to be a direct result of animals becoming emaciated from prolonged exposure to low food concentrations, a situation which renders them incapable of high filtering rates. This may explain the Type 3 functional response for field cladocerans, since zooplankton in food-limiting situations are constantly exposed to low food concentrations, and would therefore have low body carbon and consequently less energy to filter-feed. We cannot, however, use this to explain the Type 3 response for field diaptomids, since copepods in the laboratory did not appear to lose body carbon even after 72 h of feeding at very low food levels, and there was inconclusive evidence that either Diaptomus or Eudiaptomus decrease their filtering rates with acclimation period. Although Incipient Limiting Concentrations (ILC) for Daphnia ranged from 1 to 8.5 × 10³ μg 1⁻¹, more than half of these fell between 1 and 3 × 10³ μg l⁻¹, bracketing the value of 2.7 × 10² μg l⁻¹ for field cladocerans. There was, however, a great deal of variation in reported maximum ingestion rates (MIR), maximum filtering rates (MFR) and ILC values for Daphnia magna. ILC values from the few laboratory studies of freshwater copepods ranged between 0.5 to 2.8 × 10³ μg 1⁻¹, and was higher than the ILC value of approximately 0.2 × 10³ μg l⁻¹ calculated for field populations of D. minutus. Generally, there was considerable agreement among laboratory studies regarding the shape of grazing-rate and ingestion-rate curves when data were converted to similar units and presented on standardized scales.     

Rabbit brain purine nucleoside phosphorylase. Physical and chemical properties. Inhibition studies with aminopterin, folic acid and structurally related compounds.

Rabbit brain purine nucleoside phosphorylase used in this study was purified 6000-fold to apparent homogeneity and a specific activity or 50 μmol min^?1 mg ^?1 protein. A molecular weight of 70.000 daltons was determined for the native enzyme by gel filtration on Sephadex. Electrophoresis on polyacrylamide gel, in presence of sodium dodecyl sulfate, gave a subunit molecular weight of 34,500 daltons, suggesting that the enzyme is dimeric with, probably, identical subunits. The relationship of the structure of certain biologically active substances to their inhibitory action on the enzyme was examined. Folic acid and the compound d,l-6-methyl 5,6,7,8-tetrahydropterine, with similar substituents on their primary ring structure, were competitive inhibitors of the enzyme. The inhibition constants calculated were 3.37 × 10^?5M for folic acid and 3.80 × 10^?5m for d,l-6-methyl 5,6,7,8-tetrahydropterine. Aminopterin and the purine analog 8-aza-2,6-diaminopurine, with similar substituents on their primary ring structure, were noncompetitive inhibitors of the enzyme. Their respective inhibition constants were 1.50 × 10^?4 and 1.95 × 10^?4m. Erythro-9-(2-hydroxy-3-nonyl) adenine, an adenosine deaminase inhibitor, was also examined for inhibitory potency with mammalian purine nucleoside phosphorylase, and was observed to be a competitive inhibitor of this enzyme, with an inhibition constant of 1.90 × 10^?4m. The Michaelis constant for the substrate guanosine was near 6.0 × 10^?5m. Physical probe of the nature of the functional groups which participate in enzymic catalysis implicated both histidine and cysteine as the essential catalytic species. Photooxidation studies suggested a pH-dependent sensitivity of an essential catalytic group, and its probable location at the active site.     

Behavioral responses to food odor in juvenile marine fish: Acuity varies with species and fish length

This study tested the hypothesis that acuity of behavioral responses to food odor in three commercially important species of marine fish would increase as juvenile length increased. Swimming activity among two size groups of fish was measured in the presence of a series of squid extract dilutions. Increased swimming activity in juvenile Pacific halibut Hippoglossus stenolepis Schmidt, walleye pollock Theragra chalcogramma Pallas, and sablefish Anoplopoma fimbria Pallas was stimulated above threshold concentrations of squid extract, expressed as dilution from full strength. Maximum chemosensory acuity was observed in smaller (8-14 cm total length, TL) Pacific halibut and walleye pollock, while larger sablefish (15-23 cm TL) continued to develop acuity. Response thresholds were highest (10^− 3 dilution) in Pacific halibut, at intermediate levels (10^− 4-10^− 6 dilution) in walleye pollock and smaller sablefish and reached the lowest levels (10^− 13 dilution) in larger sablefish. The widely held view that dissolved free amino acids (DFAA) are the primary chemosensory stimulants for fish food searching may not be valid for sablefish, as they detected squid extract at dilutions containing DFAA that appeared to be far below ambient sea water DFAA concentrations.     

A novel response to propranolol: Contractile response in the isolated rabbit ear artery

Propranolol caused a contractile response in the isolated rabbit ear artery (EA). The concentration of propranolol causing a threshold contraction was 1.76 × 10^?6M while that causing a maximal contraction of 2.2 ± 0.18 g was 3 × 10^?5M. Higher concentrations caused tissue relaxation. Phentolamine, 10^?7 and 10^?6M reduced the propranolol-induced contractions by 50% and 90%, respectively while prazosin, 10^?8, 10^?7 and 10^?6M caused reductions of 54, 74 and 88%, respectively. Reserpinization of the rabbit with 5 mg/kg 24 hours before use eliminated the EA contractile response to tyramine but had no effect on that to propranolol. Desmethylimipramine plus deoxycorticosterone acetate enhanced the submaximal contraction of the EA to propranolol. $\text{In vitro}$ denervation with 6-hydroxydopamine (6-OHDA) decreased the response of the EA to tyramine and propranolol by 96% and 85% respectively but increased that to norepinephrine (NE) by 11%. Rabbit thoracic aorta (TA) did not respond to propranolol. In EA contracted with vasopressin o or 30 mM potassium, propranolol 10^?4 and 3 × 10^?4M caused a 20% and 100% relaxation, respectively. It is concluded that propranolol elicits a contractile response in the EA, at least in part, by direct activation of postsynaptic alpha adrenoceptors.     

Latent and active forms of collagenase in rat uterine explant cultures: regulation of conversion by progestational steroids

A latent collagenase, activatable by trypsin, has been identified in the culture media of postpartum rat uterus explants. Progesterone at a concentration of 25 × 10^?6m reduced the level of active collagenase by approximately 50%, whereas, total enzyme levels (active + latent) remained essentially constant during the first 3 days of culture. In addition, medroxyprogesterone acetate at a concentration of 1 × 10^?6m reduced active enzyme by approximately 75% while only small decreases in total enzyme were observed. After the third day of culture, total enzyme levels were also significantly decreased. These data suggest that during the first 3 days in culture the progestins prevent the conversion of latent collagenase to its active form. A fraction capable of promoting the activation of explant collagenase was detected in the culture medium and was partially separated from the collagenase. Progesterone (25 × 10^?6m) or medroxyprogesterone acetate (1 × 10^?6m) caused a 50 or 71% decrease, respectively, in the levels of the activator.     

Neutral Aminopeptidase and Dipeptidyl Peptidase IV Activities in Plasma of Monosodium Glutamate Obese and Food‐deprived Rats

Biometric parameters, glycemia and activity levels of plasma neutral aminopeptidase (APN) and dipeptidyl peptidase IV (DPPIV) were measured in monosodium glutamate obese and food‐deprived rats (MSG‐FD), to analyze the involvement of these enzymes in such situations. Plasma APN was distinguished as sensitive (PSA) (K_m = 7.8 × 10^?5 mol/l) and predominantly insensitive (APM) (K_m = 21.6 × 10^?5 mol/l) to puromycin, whereas DPPIV was sensitive (DPPIV‐DS) (K_m = 0.24 × 10^?5 mol/l) and predominantly insensitive (DPPIV‐DI) (K_m = 7.04 × 10^?5 mol/l) to diprotin A. Although unchanged in the MSG and food‐deprived animals, APM activity levels were closely correlated with body mass, Lee index, and mass of retroperitoneal fat pad in the food deprived, but not in the MSG animals. DPPIV‐DI activity levels decreased by 33% and were correlated with body mass, Lee index, and mass of periepididymal fat pad in the food‐deprived MSG rats. These data suggest that APM and DPPIV‐DI are respectively related to the downregulation of somatostatin in food‐deprived rats, and to the recovery of energy balance in MSG obese rats during food deprivation.     

Effect of food deprivation on attractiveness of food sources, containing natural and artificial sugar and protein, to three African fruit flies: Ceratitis cosyra, Ceratitis fasciventris, and Ceratitis capitata

The effects of food deprivation, age, and mating status on the responses of three fruit fly species, Ceratitis cosyra (Walker), Ceratitits fasciventris (Bezzi), and Ceratitits capitata (Wiedemann) (Diptera: Tephritidae) to natural and artificial sugar and protein food sources were investigated. Natural food sources included guava [Psidium guajava L. (Myrtaceae)] juice (a common host fruit for all three fruit fly species) and bird faeces (farm chicken). Artificial food sources included molasses (obtained from a local sugar factory) and a locally produced protein bait (the International Centre of Insect Physiology and Ecology yeast). In all species studied, sugar deprivation of immature (1–2‐day‐old) male and female flies increased their response to food odours, although it did not change their preference for the type of odour (protein or sugar). Protein deprivation of mature (14–17‐day‐old) male and female flies also increased their response to food odours compared to protein‐fed flies. Protein‐deprived females were highly attracted to odours from protein sources in particular. Odours from natural food sources, guava juice, and chicken faeces, were more attractive to food‐deprived flies than were odours from artificial sugar and protein sources. Attraction to food odours increased significantly with increasing age for protein‐deprived females of all species. For males and females of all species, nutritional state was a more important factor than mating status in influencing responses of flies to food odours. Practical implications of these findings are discussed in terms of strategies for fruit fly control using food baits.     

Suspended clay reduces Daphnia feeding rate

SUMMARY. 1. Suspended sediments often reduce cladoceran abundance in the field, and reduce the algal feeding rates of cladocerans in the laboratory. This paper explores the behavioural mechanisms by which suspended clay reduces Daphnia feeding rates. Feeding experiments using radiolabelled Cryptomonas cells showed that 50–200 mg 1-^?1 coarse suspended clay (particle size<2 μm) reduced the algal ingestion rate of Daphnia ambigua by 29–87%, but fine suspended clay (<1 μm) had no effect. Suspended clay decreased feeding rate by 60–70% at low algal concentrations (≤5×10³ cells ml^?1), but by only 27% at high algal concentrations (20×10³ cells ml^?1). Thus, the inhibitory effects of suspended clay are greater at low algal concentrations. The sudden addition (or removal) of suspended clay caused immediate reductions (or increases) in algal ingestion rate. 2. Observations of the feeding behaviour of tethered D.pulex showed that the frequency of postabdominal rejections increased greatly in the presence of suspended clay. The rejected boluses contained both algae and clay. Thoracic feeding appendage beat frequency decreased in the presence of suspended clay, decreasing the volume of water searched for food particles. 3. These behavioural responses indicate that clay reduces cladoceran feeding rate by mechanically interfering with both the collection and ingestion of algal cells. Both inhibitory effects are caused because cladocerans collect and ingest suspended clay particles. The behavioural mechanisms by which cladocerans regulate their feeding rate in very high concentrations of algal cells (rejection of excess food and reduction in thoracic limb pumping movements) are the same mechanisms responsible for the inhibition of algal ingestion rate in the presence of high concentrations of suspended clay particles.     

In situ measurements of bioluminescence response of Gonyaulax spinifera to various mechanical stimuli

A conspicuous bioluminescence during nighttime was reported in an aquaculture farm in the Cochin estuary due to Gonyaulax spinifera bloom on March 20, 2020. In situ measurements on bioluminescence was carried out during nighttime to quantify the response of G. spinifera to various mechanical stimuli. The bioluminescence intensity (BI) was measured using Glowtracka, an advanced single channel sensor, attached to a Conductivity–Temperature–Depth Profiler. In steady environment, without any external stimuli, the bioluminescence generated due to the movement of fishes and shrimps in the water column was not detected by the sensor. However, stimuli such as a hand splash, oar and swimming movements, and a mixer could generate measurable bioluminescence responses. An abundance of?~?2.7?×?10⁶ cells L^?1 of G. spinifera with exceptionally high chlorophyll a of 25 mg m^?3 was recorded. The BI in response to hand splash was recorded as high as 1.6?×?10¹¹ photons cm^?2 s^?1. Similarly, BI of?~?1–6?×?10¹⁰ photons cm^?2 s^?1 with a cumulative bioluminescence of?~?2.51?×?10¹² photons cm^?2 (for 35 s) was recorded when there is a mixer with a constant force of 494 N/800 rpm min^?1. The response of G. spinifera was spontaneous with no time lapse between application of stimuli and the bioluminescence response. Interestingly, in natural environment, application of stimulus for longer time periods (10 min) does not lower the bioluminescence intensity due to the replenishment of water thrusted in by the mixer from surrounding areas. We also demonstrated that the bioluminescence intensity decreases with increase in distance from the source of stimuli (mixer) (av. 1.84?×?10¹⁰ photons cm^?2 s^?1 at 0.2 m to av. 0.05?×?10¹⁰ photons cm^?2 s^?1 at 1 m). The BI was highest in the periphery of the turbulent wake generated by the stimuli (av. 3.1?×?10¹⁰ photons cm^?2 s^?1) compared to the center (av. 1.8?×?10¹⁰ photons cm^?2 s^?1). When the stimuli was applied vertically down, the BI decreased from 0.2 m (0.3?×?10¹⁰ photons cm^?2 s^?1) to 0.5 m (0.10?×?10¹⁰ photons cm^?2 s^?1). Our study demonstrates that the BI of G. spinifera increases with increase in mechanical stimuli and decreases with increase in distance from the stimuli.

     

Abscisic Acid-Induced Starch Accumulation in Bioenergy Crop Duckweed <Emphasis Type="Italic">Spirodela polyrrhiza</Emphasis>

Spirodela polyrrhiza, a fast-growing duckweed with high starch and low lignin content, shows promise as a feedstock for bioenergy. Abscisic acid (ABA) is a biological hormone that controls plant growth and stress response. The effects of different ABA concentrations (0, 1.0 × 10^?5, 1.0 × 10^?4, 1.0 × 10^?3, 1.0 × 10^?2, and 1.0 × 10^?1 mg/L) on duckweed biomass growth, carbon dioxide fixation, formation of photosynthetic pigments (Chlorophyll a (Chla), Chlorophyll b (Chlb), and carotenoids), the activities of soluble starch synthase (SSS) and starch branching enzyme (SBE), and the starch content of biomass were investigated in this study. ABA at concentrations lower than 1.0 × 10^?3 mg/L promoted carbon dioxide fixation, whereas it inhibited carbon dioxide fixation at concentrations over 1.0 × 10^?3 mg/L. ABA enhanced SSS and SBE activities at concentrations lower than 1.0 × 10^?2 mg/L. ABA treatment increased the content of Chla, Chlb, and carotenoids and resulted in the enhancement of starch content. Chla content gradually increased with the increasing concentration of ABA (1.0 × 10^?5 to 1.0 × 10^?2 mg/L). After culturing for 10 days, starch content in 1.0 × 10^?2 mg/L ABA medium reached 35.3% of dry weight (DW), which was the highest level in this study. This suggests that there is a great potential to develop a technology to increase starch accumulation in duckweed which can be used as an alternative to corn, sugarcane, or other food crops as a starch source.     

Acetylcholine potentiation of field stimulated rat vas deferens: A pre-synaptic muscarinic mechanism?

Acetylcholine (ACh) was found to markedly enhance the nerve stimulation induced twitch response of isolated, field-stimulated rat vas deferens (RVD). The ED₂₀₀ (concentration which enhances the twitch response to 200% of control) for this potentiation was 6 × 10^?6M with the maximum twitch response being increased by more than 3 fold (325 ± 30%). Carbachol (ED₂₀₀ = 8.5 × 10^?7M) showed identical results. With each drug the potentiation was competitively antagonized by atropine (10^?7?10^?5M). Physostigmine 10^?8?10^?6M) both enhanced the basal twitch response (215 ± 8% of control at 10^?5M) and the sensitivity of the RVD to ACh (ED₂₀₀ = 3.3 × 10^?7M) but not to carbachol. Atropine, on the other hand reduced the basal twitch response by 18 ± 3% at 10^?5M. Hemicholinium (10^?4M) also reduced the basal twitch responses by 23 ± 5%. ACh (10^?7M?10^?5M) did not modify the responses of unstimulated RVD to norepinephrine or KCl suggesting a pre-synaptic site of action. Taken together these results are compatible with the presence of a pre-junctional, excitatory muscarinic mechanism in the field stimulated RVD. That this cholinergic system may be of physiological significance is supported by the observations that atropine and hemicholinium depress while physostigmine enhances the twitch response in the absence of exogenous ACh.     

Progressive increase with time after sensitization in the functional affinity of T lymphocytes

The dose response relationship in peritoneal cell migration inhibition, elicited by various concentrations of ABA-Tyr, was studied in guinea pigs sensitized with a standard dose of ABA-Tyr. The reactivity to 2 × 10^?7 or 2 × 10^?8 mole/ml appeared at 2 wk, and remained at the maximum level from 4 wk to 8 mo after sensitization. The inhibition by 2 × 10^?9 mole/ml increased up to 4 mo and 2 × 10^?10 mole/ml was first inhibitory at $\text{6}\text{1}\text{2}$ mo. The change in the slope of the dose response curve was a property of the ABA-specific cells. As there is no B-cell response to ABA-Tyr, the finding shows that the functional affinity of specific T cells progressively increases with time after sensitization.     

Catalytic properties of three lactate dehydrogenases from potato tubers (Solanum tuberosum)

Two l-lactate dehydrogenase isoenzymes and one dl-lactate dehydrogenase could be separated from potato tubers by polyacrylamide-gel electrophoresis. The enzymes are specific for lactate, while β-hydroxybutyric acid, glycolic acid, and glyoxylic acid are not oxidized. Their pH optima are pH 6.9 for the oxidation and 8.0 for the reduction reaction.The K_m values for l-lactate for the two isoenzymes are 2.00 × 10^?2 and 1.82 × 10^?2, m. In the reverse reaction the affinities for pyruvate are 3.24 × 10^?4 and 3.34 × 10^?4, m. Both enzymes have similar affinities for NAD and NADH (3.00 × 10^?4; 4.00 × 10^?4, and 8.35 × 10^?4; 5.25 × 10^?4, m).The dl-lactate oxidoreductase may transfer electrons either to NAD or N-methyl-phenazinemethosulfate. The K_m values of this enzyme for l-lactate are 4.5 × 10^?2, m and for d-lactate 3.34 × 10^?2, m. Its affinity for pyruvate is 4.75 × 10^?4, m. The enzyme is inhibited by excess NAD (K_m = 1.54 × 10^?4, M) and has an affinity toward NADH (K_m = 5.00 × 10^?3, M) which is about one tenth of that of the two isoenzymes of l-lactate dehydrogenase.     

Carbon dynamics in an ultra-oligotrophic epishelf lake (Beaver Lake, Antarctica) in summer

1. Microbial plankton dynamics in an ultra‐oligotrophic epishelf lake (Beaver Lake, Antarctica) were investigated over an austral summer (December 2002 to January 2003). The aim was to characterise carbon cycling in an environmentally extreme lake. 2. The lake had an unusual temperature profile with peak temperatures of 1.3–1.9 °C between 20 and 25 m. Photosynthetically active radiation penetrated to the lake bottom (110 m) on occasions. The ice cover underwent marked thinning and melting during the study period. 3. Chlorophyll a concentrations were consistently low, usually below 1 μg L^?1, with highest concentrations close to the lake bottom, where the photosynthetic elements showed strong autofluorescence. Mean photosynthetic nanoflagellates ranged between 34.9 × 10⁴ L^?1 ± 33.5 (23rd December) and 130.9 × 10⁴ L^?1 ± 112.3 (4th December). Highest photosynthetic activity was usually recorded below 25 m. Rates of carbon fixation varied between 0.089 μg C L^?1 h^?1 ± 0.002 and 0.579 μg C L^?1 h^?1 ± 0.156. Primary production was limited by low temperature and orthophosphate availability. 4. Mean bacterial concentration throughout the water column ranged between 9.3 × 10⁷ L^?1 ± 1.2 (23rd December) and 14.0 × 10⁷ L^?1 ± 1.8 (28th January). Bacterial production was low, less than 10% of primary production and ranged between 2.1 ng C L^?1 h^?1 ± 0.8 and 12 ng C L^?1 h^?1 ± 0.9. Highest rates coincided with times of highest primary production. On occasion dissolved organic carbon (DOC) concentrations dropped to 20 μg L^?1, probably below accurate limits of detection, suggesting that carbon substratum and phosphorus may have limited bacterial growth. 5. Heterotrophic nanoflagellates varied significantly over the summer from a mean of 26.6 × 10⁴ L^?1 ± 14.2 (23rd December) to 133.8 × 10⁴ L^?1 ± 33.5 (14th December). They imposed a significant grazing impact on the bacterioplankton, removing in excess of 100% of bacterial production in December. 6. The total organic carbon pool [DOC and particulate organic carbon (POC)] was below 600 μg L^?1. The ratio of DOC : POC ranged between 0.44 : 1 and 2.8 : 1 in the upper 40 m of the water column, and 1.8 : 1 and 3.7 : 1 in the lower waters. The microbial plankton contributed 1–29% of POC, thus detrital POC made up the largest fraction of the POC pool. 7. Beaver Lake is an extreme lacustrine ecosystem where heterotrophic processes occasionally appear to be carbon limited. Significant summer ice‐melt, not seen in a previous opportunistic sampling, may be having an impact on the carbon cycle.     

Selective signaling of fluoride anion based on imidazole moieties

The imidazole ring unit in both 2‐(2′‐hydroxyphenyl)‐benzimidazole (ligand a) and a europium(III) complex exhibited specific luminescent responses in the presence of fluoride anions. UV‐visible and ¹H‐nuclear magnetic resonance spectra showed that the NH bond of the imidazole ring can form a hydrogen bond with added fluoride anions. The detection limits are 5 × 10^?6 m for organic ligand and 1.0 × 10^?6 m for the europium complex respectively. The response times are less than 3 s. The europium complex exhibits a linear response in a concentration range lower than 1.0 × 10^?6 m (Y = ?666.86X + 730.1). Copyright © 2011 John Wiley & Sons, Ltd.     

The Effect of Manganese-induced Cytotoxicity on mRNA Expressions of HSP27, HSP40, HSP60, HSP70 and HSP90 in Chicken Spleen Lymphocytes in Vitro

The purpose of this study was to investigate the effect of manganese (Mn)-induced cytotoxicity on heat shock proteins in chicken spleen lymphocytes. Lymphocytes were cultured in medium in the absence and presence of MnCl₂ (2?×?10^?4, 4?×?10^?4, 6?×?10^?4, 8?×?10^?4, 10?×?10^?4, and 12?×?10^?4 mmol/L) for 12, 24, 36, and 48 h in vitro. Then, the mRNA levels of HSP27, HSP40, HSP60, HSP70, and HSP90 were examined by real-time quantitative PCR. The results showed that the mRNA levels of HSP27, HSP40, HSP60, HSP70, and HSP90 in all treatment groups at all time points, except mRNA levels of HSP27 at 48 h, had the same tendency. As manganese concentration increased, the mRNA expression of the heat shock proteins first increased and then decreased. In other words, we demonstrated that the mRNA expression of the heat shock proteins was induced at lower concentrations of manganese and was inhibited at higher concentrations. Mn had a dosage-dependent effect on HSP27, HSP40, HSP60, HSP70, and HSP90 mRNA expression in chicken spleen lymphocytes in vitro.