THE IRREVERSIBLE INHIBITION OF BRAIN L-GLUTAMATE-I-DECARBOXYLASE BY (2RS,3E)-2-METHYL-3,4-DIDEHYDROGLUTAMIC ACID

Abstract— Incubation of chick embryo brain l -glutamate-1-dccarboxylase (GAD, EC 4.1.1.15) with (2RS,3E)-2-methyl-3,4-didehydroglutamic acid (MDG), a substrate analog of l -glutamic acid, results in a time-dependent irreversible inhibition of the enzymic activity. In the presence of 2.0 ± 10^-3 m inhibitor the half-life for inactivation is 11.6min. The inhibitor is a substrate for GAD and requires turnover prior to inactivating the enzyme and is therefore another example of the k _cat class of inactivator. The measured K _l is 6.6 ± 10^-4 m and the k _cat for its turnover is 1.01 ± 10^-3 s-¹ at 37°C (pH 7.2). The inhibitor has no effect on the apoenzymc or the holoenzyme treated with 1.0 ± 10^-3 m hydrazinc. Both l -and d -glutamate, but not mercaptoethanol, reduce the rate of enzymie inactivation by the inhibitor. The exceedingly high specificity implicit in the design of this inhibitor should render it useful in studies designed to uncover the physiological role of GABA.     

Mosquito density, biting rate and cage size effects on repellent tests

Mosquito biting rates and the mean duration of protection (in hours) from bites (MDPB) of Aedes aegypti and Anopheles quadrimaculatus , using the repellent 'deet' ( N , N -diethyl-3-methylbenzamide) on a 50 cm² area of healthy human skin, were observed in small (27 l), medium (≈65 l) and large (125 l) cages containing low, medium or high densities of mosquitoes: respectively, 640, 128 or 49 cm³ of cage volume per female. At the initial treatment rate of ≈ 0.4 μl/cm² (1 ml of 25% deet in ethanol on 650 cm² of skin), the MDPB for deet against Ae. aegypti ranged from 4.5 to 6.5 h and was significantly less (5.0 ± 0.8 h) in large cages compared with medium (6.2 ± 0.9 h) and small (6.2 ± 0.8 h) cages, regardless of the density. Against An. quadrimaculatus the MDPB for deet 0.4 μl/cm² was 1.5–8.0 h, less in small (3.7 ± 2.3 h) and large (2.2 ± 1.1 h) cages at medium (3.7 ± 2.3 h) and high (2.5 ± 1.7 h) mosquito densities, and was longest in medium cages (6.2 ± 2.6 h) at low mosquito densities (5.8 ± 2.8 h). With equinoxial photoperiodicity (light on 06.00–18.00 hours) the biting rate was influenced by the time of observation (08.00, 12.00, 16.00 hours) for Ae. aegypti but not for An. quadrimaculatus. For both species, the biting rate was inversely proportional to mosquito density and the MDPB. The shortest MDPBs were obtained in large cages with high densities of mosquitoes and longest protection times occurred in medium sized cages with low mosquito densities.     

Vasopressin-enhanced urea transport by rat inner medullary collecting duct cells in culture

Abstract. The distal inner medullary collecting duct (IMCD) is critical in the urinary concentrating process, in part because it is the site of vasopressin (AVP)-regulated permeability to urea. The purpose of these experiments was to develop a cell culture model of the IMCD on permeable structure and to characterize the responsiveness to AVP. Rat IMCD cells were grown to confluence on collagen-coated Millipore filters glued onto plastic rings. To assess the time required to achieve confluence, the transepithelial resistance was measured periodically and was found to be stable after 2 weeks, at a maximal value of 595 ± 22 ω cm². In separate monolayers the effect of AVP on inulin and urea permeability was determined. While inulin permeability was unchanged after AVP, urea permeability increased from 6.0 ± 0–4 to peak values of 16.0 ± 3–8(10nM),23.1 ± 3–9(1 μM)and28 1 ± 4–9(10μM) X 10^-6cms^-1 ( n = 24). In 10 other monolayers, after the addition of 1 mM 8-Br-cAMP, urea permeability increased from 5.1 ±0–3 to 8.1 ± 1–6 times 10^-6 cm s^-1 and, after 8-Br-cAMP +3-isobutyl-l-methylxanthine, to 12.2 ± 0–7 times 10^-6 cms^-1. We conclude that rat IMCD cells grown in culture exhibit the characteristics of a 'tight' epithelium. Inulin and urea permeability are not different in the absence of AVP, consistent with high resistance junctional complexes. Furthermore, IMCD cells retain the capacity for AVP-regulated urea permeability, a characteristic feature of this nephron segment in vivo.     

THE UPTAKE OF γ-[3H]AMINOBUTYRIC ACID BY SLICES FROM VARIOUS REGIONS OF RAT BRAIN AND THE EFFECT OF LITHIUM

Abstract— Slices from various regions of rat brain, incubated at 25°C, rapidly accumulate [³H]GABA from the surrounding medium until after 60min tissue:medium ratios as high as 300 may be achieved. Kinetic analysis has demonstrated two distinct uptake systems for GABA in all the brain regions examined. One system has a relatively high substrate affinity ( K_m = 1.2 ± 10^-5 M) while the other has a lower affinity ( K_m = 4 ± 10^-4 M). Studies at low GABA concentration (5 ± 10^-8 M), as well as estimates of maximum velocities, have shown that the distribution of the high affinity uptake system is heterogeneous. Cortex, hypothala mus, midbrain and hippocampus have relatively high uptake rates while the striatum, cerebellum and pons and medulla have a lower uptake rate. Maximum velocities for the low affinity uptake system show much less regional variation.
Lithium, either added to the incubation medium or fed to rats, had no effect on the uptake of GABA by cortical slices.     

Biological activity of 6-(2,3,4-trihydroxy-3-methylbutylamino)purine, an oxidation product of zeatin

6-(2,3,4-Trihydroxy-3-methylbutylamino)purine was identified as an oxidation product of cis -zeatin and is biologically as active as the parent compound. A comparison of trans -zeatin, cis -zeatin and (±)-dihydrozeatin indicated that trans -zeatin and (±)-dihydrozeatin were more active in the soybean callus bioassay than cis -zeatin. Both the trans - and cis -isomers of zeatin did, however, give an optimum response at 10^-5 M. Dihydrozeatin was more active at concentrations of 10^-6 and 10^-5 M than trans -zeatin. The significance of the formation of 6-(2,3,4-trihydroxy-3-methylbutylamino)purine with respect to stereochemistry and the oxidation of cytokinins with an unsaturated isopentenyl side chain is discussed.     

Formulation of a flowable liquid concentrate of Bacillus thuringiensis serotype H-14 spores and crystals as mosquito larvicide

A.O. EJIOFOR AND N. OKAFOR. 1991. Bacillus thuringiensis serotype H-14 spores and crystals, produced in 5 1 fermenters, were centrifuged and resuspended in emulsified palm olein to give 3.2 × 10¹¹ colony forming units (cfu)/ml. The suspension was mixed with a cassava—molasses—palm olein—charcoal (CMPC-2) mixture which served as the carrier, adhesive, dispersant and protectant. The final concentration of the formulation was 3.2 × 10⁹ cfu/ml. The lethal concentrations capable of killing 50% of the test population (LC₅₀) of CMPC-2 during 0, 1 and 2 years of storage at 32 ± 4.C were 0.056, 0.058 and 0.058 mg/ml respectively as against 0.054, 0.051 and 0.054 mg/ml for the Institut Pasteur Standard—1978 (IPS-78) during the corresponding period. The² tests showed that the results were homogeneous at P = 0.05. The relative potencies of the preparation were 964.3, 879.3 and 931 International toxic units (ITU) Aedes aegypti as compared with the 1000 ITU assigned to IPS-78. At 95% confidence limits there was no significant difference between the potencies of CMPC-2 and IPS-78. Field tests showed that CMPC-2 provided between 87.5 and 100% control of natural populations of Aedes spp. and Cutex spp. Sedimentation tests showed that CMPC-2 settled markedly during storage. This, therefore, required that the product be thoroughly shaken before use.     

Effect of 2-chloroethylphosphonic acid on capsule formation and alkaloid content in Papaver somniferum

Application of different concentrations of ethephon (2-chloroethylphosphonic acid) to Papaver somniferum L. at the times of stem elongation, bud, and capsule formation produced different effects. Ethephon (10^-2 M ) retarded growth of the plant and inhibited capsule formation during stem elongation, significantly reduced capsule size during the flowering period, but did not alter capsule development during capsule formation. When applied during the period of stem elongation, ethephon (10^-3 M and 10^-4 M ) reduced capsule size; alkaloid accumulation was reduced by ethephon at a concentration of 10^-3 M , but slightly increased by 10^-4 M . Ethephon (10^-3 M and 10^-4 M ) did not alter capsule development or alkaloid content significantly when applied during bud formation, but stimulated capsule size and alkaloid content when applied during capsule formation. Pretreating the plants with Ag⁺ (silver nitrate) did not reverse the ethephon effect. The results suggest that capsule maturation and alkaloid accumulation in P. somniferum are modified by ethylene, which is produced as a result of exogenous ethephon treatment.     

The cytotoxic and photodynamic inactivation of micro-organisms by Rose Bengal

Rose Bengal was cytotoxic to the following bacteria at the concentrations given in parentheses (highest concentrations of dye in mol/1 at which growth occurred on nutrient medium): Brochothrix thermosphacta and Deinococcus radiodurans (1 times 10^-6 or less); Streptococcus, Micrococcus, Staphylococcus, Bacillus, Arthrobacter and Kurthia spp. (1 times 10^-5–1 x 10^-4), and Pseudomonas spp. and Enterobacteriaceae (5 times 10^-3–1 x 10^-2 or greater). These organisms were killed rapidly when suspended in illuminated (170 μE/m²/s) solutions of Rose Bengal (1 times 10^-4 mol/1) providing oxygen was present. Singlet oxygen was identified as the lethal agent, because the rate of killing was increased by dissolving the dye in deuterium oxide while the organisms were protected against photoinactivation by L-histidine or crocetin. Yeasts from chilled foods were killed in illuminated solutions of Rose Bengal but a light intensity of 315 μE/m²/s was needed for a death rate comparable with that of bacteria. The yeasts present in a range of chilled meat and dairy products failed to form colonies on Rose Bengal (5 times 10^-5 mol/1) media exposed continuously to modest illumination (55–80 μE/m²/s).     

2,4-Dichlorophenoxyacetic acid inhibition of potassium transport in barley seedlings

Growth, potassium uptake and translocation as well as transpiration rates were measured in intact low-salt barley seedlings ( Hordeum vulgare L. cv. Union) in the presence of different 2,4-D concentrations at pH 6.5. Growth was only affected at 10^-3 M .
Above 10^-7 M 2,4-D both uptake by the roots and transport to the shoots were inhibited. The inhibition at 10^-5 M remained constant for at least 24 h. Furthermore inhibition of uptake was measurable within 1 h. Excised roots and roots of intact plants showed the same uptake pattern.
It is suggested that the observed effects were caused by 2,4-D-induced changes in uptake and translocation systems in the roots. Pre-treatment with 10^-5 M 2,4-D had no effect upon subsequent potassium uptake. Transpiration was reduced within 1 h in 10^-4 or 10^-3 M 2,4-D, probably due to changes in water transport or root permeability.     

A behavioural test of the sensitivity of a nocturnal mosquito, Anopheles gambiae, to dim white, red and infra-red light

Abstract. A behavioural test was used to determine the light sensitivity of the nocturnal mosquito Anopheles gambiae Giles s.s. to low intensities of 'white' light (tungsten filament), 'red' light (white light filtered by a darkroom safelight filter) and 'infra-red' light) of two types (white light filtered by a λ>700 nm filter, and light-emitting diodes with λ>900 nm). Mosquitoes were placed in a 20 cm diameter flight-tunnel and their 'optomotor' response to a pattern of stripes moving across their visual field (at 14.5 cm s^-1) was recorded with infra-red-sensitive video. In free-flight, with ample light, the mosquitoes controlled their flight speed and direction in relation to the stripe movement, so that the stripes always appeared to move across their visual field from front to back. They did this by flying either with the moving stripes fast enough to overtake them (19.5 ± 0.7 cm s^-1), or against them more slowly (10.3 ± 0.7 cm s^-1)- The net ground speed of the mosquitoes was thus c. 4–5 cm s^-1. This response was significant down to 10^-5 W m^-2 in 'white' light, and 10^-3 W m^-2 in 'red' light. At light intensities below threshold and in infra-red light, however, they appeared to fly at random with respect to the stripe movement. The assumption commonly made, that mosquitoes do not 'see' in red light, may thus have to be revised.     

CHARACTERISTICS OF D-GLUCOSAMINE UPTAKE BY RAT BRAIN SYNAPTOSOMES

Abstract— The uptake of D-glucosamine by rat brain synaptosomes is studied as a function of time, temperature and synaptosomal protein and substrate concentrations. The rate of D-glucosamine uptake, after correcting for simple diffusion, obeys Michaelis-Menten kinetics. The apparent kinetic constants for the uptake process are K_m = 2.5 0.8 m m , V_max = 3.7 ± 1.2 nmol/mg protein/min. D-Glucose, D-mannose, 2-deoxy-D-glucose and 3-0-methyl-o-glucose are potent inhibitors of D-glucosamine uptake. 2-Deoxy-D-glucose and D-glucosamine inhibit the uptake of one another in a simple competitive manner, indicating their sharing of a common transport system. Cytochalasin B, phloretin and phloridzin are powerful competitive inhibitors of D-glucosamine uptake with apparent inhibitor constants ( K₁ ) of 7.0 × 10^-5, 2.3 × 10^-3 and 0.4 mM, respectively. The uptake is unaffected by Na⁺, Li⁺ and Mg²⁺, partially inhibited by NH₄⁺, Mn²⁺ and Ca²⁺, and slightly stimulated by PO₄-ions. D-Glucosamine uptake is also sensitive to inhibition by several sulfhydryl reagents, thus implying the involvement of sulfhydryl groups in the transport process. The apparent affinity constants for synaptosomal transport for both D-glucosamine and 2-deoxy-D-glucose are about 4 times greater in 7-day-old than in the adult rat brains.     

Interaction of triacontanol with gibberellin in control of lettuce seed germination

Triacontanol at concentrations from 2.3 × 10^-9 M to 2.3 × 10^-7 M did not affect the germination of lettuce ( Lactuca sativa L., cv. Grand Rapids) seeds in darkness, stimulated by light at 25°C or by benzyladenine at 31°C. Stimulation of seed germination by gibberellin A₃ (10^-5 M ) was significantly inhibited by triacontanol; the most effective concentration was 4.6 × 10^-8 M. Pulse experiments demonstrated that triacontanol was ineffective when applied later than gibberellin, whereas an inverse sequence of treatment caused an inhibition comparable to that resulting from continuous treatment of seeds with both factors. Possible interaction of triacontanol with gibberellin receptor is discussed.     

Longevity of the freshwater anostracan Streptocephalus mackini (Crustacean: Anostraca) in relation to food (Chlorella vulgaris) concentration

SUMMARY 1. Temporary ponds are inhabited by a variety of invertebrates, of which anostracans are an important group. We studied the lifetables of male and female anostracan Streptocephalus mackini at 3 algal concentrations (0.5 × 10⁶, 1.0 × 10⁶ and 1.5 × 10⁶ cells mL⁻¹).
2. Regardless of sex, S. mackini showed better survivorship at lower food levels. The longest average lifespan observed was 85 ± 2 days for males fed Chlorella at 0.5 × 10⁶ cells mL⁻¹.
3. Both net reproductive rate and generation time decreased with increasing food level. The highest net reproductive rate was about 120 cysts per female. The longest generation time of about 40 days, observed at 0.5 × 10⁶ cells mL⁻¹, was more than three times that at 1.5 × 10⁶ cells mL⁻¹.
4. The rate of population increase ( r ) was nearly the same (0.31 ± 0.06) at high (1.5 × 10⁶ cells mL⁻¹) and intermediate (1.0 × 10⁶ cells mL⁻¹) food levels. The r -value at low food level (0.5 × 10⁶ cells mL⁻¹ of Chlorella ) was 0.20 ± 0.01 per day.     

Effect of some factors on determination of viable microbial cells by peroxyoxalate chemiluminescence method

The effects of physical and chemical factors on the production of H₂O₂ from Escherichia coli cells were studied. When 20 mmol 1^-1 Tris-HCl buffer was used for this purpose the electron transport system (ETS) showed the highest activity at pH 7.6-8.2. KCN promoted the production of H₂O₂ from E. coli cells, and the optimum concentration was changed in different reaction times and pH values. Glucose, 5 mg ml^-1, increased the ETS activity about twofold. The other substrates and surfactants did not increase the chemiluminescence intensity. NaNO₂ and Na₂SO₄ in inorganic salts significantly reduced the ETS activity above 70%. In addition, the optimum temperature for the production of H₂O₂ was 30°C in this study. When glucose (5 mg ml^-1) and KCN (0.2 mmol 1^-1) were added to the reaction buffer containing 0.5 mmol 1^-1 menadione, the detectable minimum cell densities (averages of triplicate assay) of E. coli, Enterobacter cloacae and Serratia marcescens were 5 times 10³ cells ml^-1, 10⁴ cells ml^-1 and 10⁴ cells ml^-1 respectively.     

Effects of pollutants in fresh waters on European non-salmonid fish I: Non-metals

As part of a programme of acquiring data for preparing standards to safeguard European, nonsalmonid, freshwater fish from pollution, toxicity tests were carried out in hard, well-aerated water. Asymptotic median lethal concentrations (LC50s) of undissociated ammonia, cyanide, nitrite and phenol to one or more of three species were determined. The LC50s were as follows: to common carp 16mg1^-1 as NO₂–N; to perch 0.1 mg1^-1 as HCN; to roach 0.35 mg1^-1 as NH₃-N, 0-11mg1^-1 as HCN, 10.1 mg1^-1 asNO₂-Nand 10mg^-1 as phenol. In order to define these LC50s, exposure periods within the range 0.3 days (phenol) to 14 days (nitrite) were required. Comparisons are made with other data and the tentative water quality 'criteria' proposed by the European Inland Fisheries Advisory Commission.     

3,5-Dichlorophenoxyacetic acid as a growth retardant

Tomato seedlings, grown in the glasshouse, were sprayed with solutions of 3,5-dichlorophenoxyacetic acid as sodium salt at 2 times 10^-5, 4 times 10^-5 and 10^-4 M. The treated plants became dark-green, dwarfed, and compact. After 6–7 weeks normal growth was resumed. Measurements and analytical data on treated and control plants are presented.     

A Simple Cranial Window Technique for Optical Monitoring of Cerebrocortical Microcirculation and NAD/NADH Redox State. Effect of Mitochondrial Electron Transport Inhibitors and Anoxic Anoxia

Abstract: Fluorescence of NADH and vascular volume of the brain cortex of chloralose-anesthetized cats were measured by surface fluororeflectometry. A cranial window and superfusion technique was elaborated for the topical inhibition of mitochondrial electron transport in the brain cortex by amytal (inhibits at site I) and cyanide (inhibits at site III). The changes in NAD/NADH redox state and CVV evoked by these electron transport inhibitors were compared with those elicited by anoxic anoxia. Amytal (10^-3-10^-1 M ) and cyanide (10^-5-10^-2 M ) resulted in a concentration-dependent and reversible increase in cortical NAD reduction and vascular volume, but the cerebrocortical vessels were almost completely dilatated long before maximum NAD reduction was reached. Cyanide at 10^-2 M increased cortical NAD reduction and vascular volume as much as anoxic anoxia. Amytal at 10^-1 M induced approximately half of the NAD reduction evoked by 10^-2 M cyanide or anoxic anoxia, but resulted in only slightly less vasodilatation than that following cyanide and anoxic anoxia. Since amytal inhibits mitochondrial electron transport at site I—and cyanide and anoxia at site III—but induces a comparable degree of vasodilatation, it is concluded that cytochrome oxidase cannot be the single molecular oxygen sensor in the brain cortex.     

A developmental study of Glycine max cell and protoplast isolation in relation to leaf age and photosynthetic competence

Leaf mesophyll cells were isolated from developing first trifoliate leaves of Glycine max (L.) Merr cv. Fiskeby V using a mechanical isolation procedure combined with low speed centrifugation. Cell yields of 17 ± 1.7% were routinely obtained with 55–75% intactness, as assessed by staining techniques, fluorescence transients and the ability of cells to convert to protoplasts after enzyme treatment. Rates of leaf photosynthesis were maximal in 27-day-old plants [280 μmol O₂ evolved (mg chlorophyll)^-1h^-1], from which isolated cells and protoplasts gave rates of up to 140 μmol O₂ evolved (mg chlorophyll)^-1 h^-1. Results are discussed in relation to leaf development and cell status during the attainment of photosynthetic competence.     

Effect of alcohols on the association of photosynthetic fructose-1,6-bisphosphatase to thylakoid membranes

Aliphatic alcohols have a positive effect on the assoociation of pea ( Pisum sativum L. cv. Lincoln) chloroplast fructose- 1,6-bisphosphatase (FBPase; EC 3.1.3.11) with thylakoid membranes. The alcohol concentration needed to obtain a fixed percentage of enzyme association decreased with increased length of the aliphatic chain of the alcohol; maximum binding was obtained when the lysis medium contained, in molar fractions (or v/v percentages): 48×10^-4(T4 (2.4%), 26×10^-3 (10%), 40×10^-3 (15%), 76×10^-3 (21%), and 13×10^-2 (24%), of 1-butanol, 1-propanol, 2-propanol, ethanol, and methanol, respectively. A good correlation of binding with the octanol/water partition coefficient was observed. Since this coefficient constitutes a measure of hydrophobicity, we suggest that the binding of FBPase to the membranes occurs via hydrophobic clusters of both components.