Analysis of the separation of gadolinium isotopes by the ICR method

The problem of separating gadolinium isotopes is discussed. The parameters of isotope separation in a plasma by the ICR method are estimated for a device with given operating parameters. The mean transverse energy 〈E_⊥〉 of the heated ions of the ¹⁵⁷Gd isotope and the heating efficiency η are calculated as functions of the frequency of the RF electric field in the plasma. The dependence of the heating efficiency η on the longitudinal temperature of the plasma flow is investigated. The issue of how the concentration of the target isotope ions at the collector plate depends on the longitudinal coordinate measured from the front edge of the plate is analyzed for different values of the frequency detuning parameter. The extraction coefficient Г for the target isotope is calculated as a function of the distance b between the collector plates for different frequency detunings.     

Whole-cell hydroxylation of n-octane by Escherichia coli strains expressing the CYP153A6 operon

CYP153A6 is a well-studied terminal alkane hydroxylase which has previously been expressed in Pseudomonas putida and Escherichia coli by using the pCom8 plasmid. In this study, CYP153A6 was successfully expressed in E. coli BL21(DE3) by cloning the complete operon from Mycobacterium sp. HXN-1500, also encoding the ferredoxin reductase and ferredoxin, into pET28b(+). LB medium with IPTG as well as auto-induction medium was used to express the proteins under the T7 promoter. A maximum concentration of 1.85?μM of active CYP153A6 was obtained when using auto-induction medium, while with IPTG induction of LB cultures, the P450 concentration peaked at 0.6–0.8?μM. Since more biomass was produced in auto-induction medium, the specific P450 content was often almost the same, 0.5–1.0?μmol P450 g _DCW ^?1 , for both methods. Analytical scale whole-cell biotransformations of n-octane were conducted with resting cells, and it was found that high P450 content in biomass did not necessarily result in high octanol production. Whole cells from LB cultures induced with IPTG gave higher specific and volumetric octanol formation rates than biomass from auto-induction medium. A maximum of 8.7?g octanol L _BRM ^?1 was obtained within 24?h (0.34?g L _BRM ^?1 ?h^?1) with IPTG-induced cells containing only 0.20?μmol P450 g _DCW ^?1 , when glucose (22?g L _BRM ^?1 ) was added for cofactor regeneration.     

Spectroscopic Studies on the Binding of Cobalt(II) 1,10-Phenanthroline Complex to Bovine Serum Albumin

The binding interaction of the cobalt(II) 1,10-phenanthroline complex (Co(phen) ₃ ²⁺ , phen = 1,10-phenanthroline) with bovine serum albumin (BSA) was investigated by fluorescence spectroscopy combined with UV–Vis absorption and circular dichroism measurements under simulative physiological conditions. The experiment results showed that the fluorescence intensity of BSA was dramatically decreased owing to the formation of Co(phen) ₃ ²⁺ –BSA complex. The corresponding association constants (K _a) between Co(phen) ₃ ²⁺ and BSA at four different temperatures were calculated according to the modified Stern–Volmer equation. The enthalpy change (ΔH°) and entropy change (ΔS°) were calculated to be ?2.73 kJ mol^?1 and 82.27 J mol^?1?K^?1, respectively, which suggested that electrostatic interaction and hydrophobic force played major roles in stabilizing the Co(phen) ₃ ²⁺ –BSA complex. Site marker competitive experiments indicated that the binding of Co(phen) ₃ ²⁺ to BSA primarily took place in site I of BSA. A value of 4.11 nm for the average distance r between Co(phen) ₃ ²⁺ (acceptor) and tryptophan residues of BSA (donor) was derived from Förster’s energy transfer theory. The conformational investigation showed that the presence of Co(phen) ₃ ²⁺ resulted in the change of BSA secondary structure and induced the slight unfolding of the polypeptides of protein, which confirmed the microenvironment and conformational changes of BSA molecules.     

Competitive blockage of the sodium channel by intracellular magnesium ions in central mammalian neurones

The aim of this study was to determine from macroscopic current analysis how intracellular magnesium ions, Mg _i ²⁺ , interfere with sodium channels of mammalian neurones. It is reported here that permeation across the sodium channel is voltage- and concentration-dependently reduced by Mg _i ²⁺ . This results in a general reduction of sodium membrane conductance and an outward sodium peak current at large positive potentials. 30 mM Mg _i ²⁺ leads to a negative shift of voltage dependence of sodium channel gating parameters, probably due to the surface potential change of the membrane. This shift alone is, however, insufficient to explain the reduction of outward sodium currents. The blockage by Mg _i ²⁺ is decreased upon increasing intracellular or extracellular Na⁺ concentration, which suggests that Mg?' interferes with sodium permeation by competitively occupying sodium channels. Using a kinetic model to describe the sodium permeation, the dissociation constant (at zero membrane potential) of Mg _i ²⁺ for the sodium channel has been calculated to be 8.65 ± 1.51 mM, with its binding site located at 0.26 ± 0.05 electrical distance from the inner membrane. This dissociation constant is smaller than that of Na _i ⁺, which is 83.76 ± 7.60 mM with its binding site located at 0.75 ± 0.23. The low dissociation constant of Mg _i ²⁺ reflects its high affinity for the sodium channel.     

Effect of long-term fertilization and cropping on the potassium supplying capacity of soils

Soil samples from a long term field experiment, to study the K depletion pattern, were analysed for K. The values of supply parameters pK?1/2p (Ca+Mg) and free energy δG _r ⁰ were calculated using the data on water soluble and exchangeable cations. Correlation coefficient values between pK?1/2p (Ca+Mg) vs. total K removed, K removal by pearl millet in 1980 and soil available potassium were positive and statistically significant. This indicated that these soils have reached the stage where they would start responding to potassium application. Also, negative but significant correlation of δG _r ⁰ with pK?1/2p (Ca+Mg) and available K, were found. δG _r ⁰ values were positive indicating the affinity of such soils for K and the values, for K fertilized plots were lower in comparison to plots where no K was applied. pK?1/2p (Ca+Mg) parameter was found to be a better measure of K availability over δG _r ⁰ due to either fixation of K or greater contribution of nonexchangeable K fraction towards plant utilized K.     

Multistage affinity cross-flow filtration: mathematical modelling and analysis

A multistage affinity cross-flow filtration (mACFF) process for protein purification is proposed. The process is mathematically modelled taking into account a case of rapid equilibrium binding of a target protein to its macroligand. The process performance, i.e., dimensionless breakthrough volume (Q _b ⁺ )and recovery yield (REC) to obtain a desired purity is analysed by computer simulations. The results indicate that Q _b ⁺ increases with the increase of stage number (n) due to the increase of affinity binding efficiency. In addition, REC also increases with the increase of n, especially for lower affinity systems, even though the feed loading is the same as the corresponding breakthrough volume that increases with n. Thus both feed loading and recovery yield can be enhanced by raising the stage number. Incompletely permeable membranes reject the target and contaminant proteins. So they delay the appearance of the breakthrough point and compromise the contaminant washing efficiency. Hence although Q _b ⁺ increases with the increase of membrane rejection coefficient (R), REC decreases when the feed loading equals that of Q _b ⁺ . However, when the feed loading is kept unchanged and equals Q _b ⁺ at R=0, REC does not decrease, but slightly increases with the increase of R. This result indicates that incompletely permeable membranes may also be employed for the mACFF process. In general, the model gives a predictive evaluation of the mACFF process successfully.     

Production of H 3 + ions in low-energy collisions between hydrogen molecular ions

The effective cross section for the H ₂ ⁺ + H ₂ ⁺ → H ₃ ⁺ + p reaction in the energy range 5.7–11.5 eV is measured by the split beam method. The cross-section maximum at an energy of ～8 eV is related to the production of the H ₄ ⁺⁺ compound system. The reaction threshold W _thr ≈5 eV provides evidence in favor of the classical model with the H ₂ ⁺ ion charge fixed on one of the two nuclei during the entire collision event.     

Ionic balance,proton efflux,nitrate reductase activity and growth ofHippophaë rhamnoides L. ssp.rhamnoides as influenced by combined-N nutrition or N2 fixation

Growth of 2-month-old nonnodulatedHippophaë rhamnoides seedlings supplied with combined N was compared with that of nodulated seedlings grown on zero N. Plant growth was significantly better with combined N than with N₂ fixation and, although not statistically significant for individual harvests, tended to be highest in the presence of NH ₄ ⁺ , a mixture of NH ₄ ⁺ and NO ₃ ^? producing the highest yields. Growth was severely reduced when solely dependent on N₂ fixation and, unlike the combined-N plants, shoot to root ratios had only slightly increased after an initial decrease. An apparently insufficient nodule mass (nodule weight ratio <5 per cent) during the greater part of the experimental period is suggested as the main cause of the growth reduction in N₂-fixing plants. Thein vivo nitrate reductase activity (NRA) of NO ₃ ^? dependent plants was almost entirely located in the roots. However, when grown with a combination of NO ₃ ^? and NH ₄ ⁺ , root NRA was decreased by approximately 85 per cent.H. rhamnoides demonstrated in the mixed supply a strong preference for uptake of N as NH ₄ ⁺ , NO ₃ ^? contributing only for approximately 20 per cent to the total N assimilation. Specific rates of N acquisition and ion uptake were generally highest in NO ₃ ^? +NH ₄ ⁺ plants. The generation of organic anions per unit total plant dry weight was approximately 40 per cent less in the NH ₄ ⁺ plants than in the NO ₃ ^? plants. Measured extrusions of H⁺ or OH^? (HCO ₃ ^? ) were generally in good agreement with calculated values on the basis of plant composition, and the acidity generated with N₂ fixation amounted to 0.45–0.55 meq H⁺. (mmol N_org)^?1. Without acidity control and in the presence of NH ₄ ⁺ , specific rates of ion uptake and carboxylate generation were strongly depressed and growth was reduced by 30–35 per cent. Growth of nonnodulatedH. rhamnoides plants ceased at the lower pH limit of 3.1–3.2 and deterioration set in; in the case of N₂-fixing plants the nutrient solution pH stabilized at a value of 3.8–3.9 without any apparent adverse effects upon plant performance. The chemical composition of experimental and field-growing plants is being compared and some comments are made on the nitrogen supply characteristics of their natural sites.     

Nitrate-use traits of understory plants as potential regulators of vegetation distribution on a slope in a Japanese cedar plantation

Background and aims

Plant physiological traits and their relation to soil N availability was investigated as regulators of the distribution of understory shrub species along a slope in a Japanese cedar (Cryptomeria japonica) plantation in central Japan.

Methods

At the study site, previous studies demonstrated that both net and gross soil nitrification rates are high on the lower slope and there are dramatic declines in different sections of the slope gradient. We examined the distributions of understory plant species and their nitrate (NO ₃ ^? -N) use traits, and compared the results with the soil traits.

Results

Our results show that boundaries between different dominant understory species correspond to boundaries between different soil types. Leucosceptrum stellipilum occurs on soil with high net and gross nitrification rates. Hydrangea hirta is dominant on soil with high net and low gross nitrification rates. Pieris japonica occurs on soil with very low net and gross nitrification rates. Dominant understory species have species-specific physiological traits in their use of NO ₃ ^? -N. Pieris japonica lacks the capacity to use NO ₃ ^? -N as a N source, but other species do use NO ₃ ^? -N. Lindera triloba, whose distribution is unrelated to soil NO ₃ ^? -N availability, changes the extent to which it uses NO ₃ ^? -N in response to soil NO ₃ ^? -N availability.

Conclusions

Our results indicate that differences in the physiological capabilities and adaptabilities of plant species in using NO ₃ ^? -N as a N source regulate their distribution ranges. The identity of the major form of available soil N is therefore an environmental factor that influences plant distributions.     

Calculation of the ion distribution function over transverse velocities under ICR heating conditions and separation parameters of a collector of heated ions

The ion distribution function over transverse velocities and the ion heating efficiency (which is defined as the fraction η of ions heated above a certain energy W_min) are calculated in the context of a plasma method for isotope separation on the basis of ion cyclotron resonance heating. The ion distribution function over longitudinal velocities is assumed to be linear in the range of low velocities. It is shown that, when the ions are heated to high energies, the averaged ion distribution function over transverse velocities becomes highly nonequilibrium and has two peaks. Results are presented from calculations of the ion heating efficiency η for W_min=40 eV and for different values of the parameter p that characterizes the ratio of the wavelength λ of the antenna electric field to the length L of the heating region. The relative roles of the time-of-flight and the Doppler broadening are analyzed, and the separation parameters of a collector of heated ions are estimated.     

Relation between electron exchange and nuclear vibrations in the H 2 + +H 2 + → H 3 + +p exothermic ion-molecular reaction

The effective cross section for the H ₂ ⁺ +H ₂ ⁺ → H ₃ ⁺ +p reaction in the energy range 5.7–11.5 eV is measured by the split beam method. The maximum of the cross section at an energy of ～8 eV is related to the production of the H ₄ ⁺⁺ compound system. The reaction threshold W _thr≈5 eV provides evidence in favor of the classical model of the H ₂ ⁺ ion with the charge fixed on one of the nuclei throughout the collision event.     

Modification of the canonical profile transport model on the basis of new DIII-D experiments

Recent DIII-D experiments have shown that the stiffness of the ion temperature profile κ _i ^PC in the region 0.4 < ρ < 0.7 increases by one order of magnitude with increasing radius. At ρ < 0.4, the stiffness is low and the ion temperature profile is “soft.” The stiffness of the temperature profile also increases with decreasing the toroidal rotation velocity. The approximation of the experimental stiffness profiles allows one to modify the canonical profile transport model. The heat conductivity κ _i ⁰ in the plasma core is determined by minimizing the r.m.s. deviations of the calculated ion temperature from the measured one. This procedure also makes it possible to determine how κ _i ⁰ depends on the central ion temperature.     

Charge separation in Rhodobacter sphaeroides mutant reaction centers with increased midpoint potential of the primary electron donor

Primary charge separation dynamics in four mutant reaction centers (RCs) of the purple bacterium Rhodobacter sphaeroides with increased midpoint potential of the primary electron donor P (M160LH, L131LH, M197FH, and M160LH + L131LH + M197FH) have been studied by femtosecond transient absorption spectroscopy at room temperature. The decay of the excited singlet state in the wild-type and mutant RCs is complex and has two main exponential components, which indicates heterogeneity of electron transfer rates or the presence of reverse electron transfer reactions. The radical anion band of monomeric bacteriochlorophyll B_A at 1020 nm was first observed in transient absorbance difference spectra of single mutants. This band remains visible, although with somewhat reduced amplitude, even at delays up to tens of picoseconds when stimulated emission is absent and the reaction centers are in the P⁺H _A ^? state. The presence of this band in this time period indicates the existence of thermodynamic equilibrium between the P⁺B _A ^? H_A and P⁺B_AH _A ^? states. The data give grounds for assuming that the value of the energy difference between the states P*, P⁺B _A ^? H_A, and P⁺B_AH _A ^? at early times is of the same order of magnitude as the energy kT at room temperature. Besides, monomeric bacteriochlorophyll B_A is found to be an immediate electron acceptor in the single mutant RCs, where electron transfer is hampered due to increased energy of the P⁺B _A ^? state with respect to P*.     

Dark induction of nitrate reductase in the halophilic alga Dunaliella salina

The effect of nitrogen starvation on the NO₃-dependent induction of nitrate reductase (NR) and nitrite reductases (NIR) has been investigated in the halophilic alga Dunaliella salina. When D. salina cells previously grown in a medium with NH ₄ ⁺ as the only nitrogen source (NH ₄ ⁺ -cells) were transferred into NO ₃ ^? medium, NR was induced in the light. In contrast, when cells previously grown in N-free medium were transferred into a medium containing NO ₃ ^? , NR was induced in light or in darkness. Nitrate-dependent NR induction, in darkness, in D. salina cells previously grown at a photon flux density of 500 umol · m^?2 s^?1 was observed after 4 h preculture in N-free medium, whilst in cells grown at 100 umol · m^?2 s^?1 NR induction was observed after 7–8 h. An inhibitor of mRNA synthesis (6-methylpurine) did not inhibit NO ₃ ^? -induced NR synthesis when the cells, previously grown in NH ₄ ⁺ medium, were transferred into NO ₃ ^? medium (at time 0 h) after 4-h-N starvation. However, when 6-methylpurine was added simultaneously with the transfer of the cells from NH ₄ ⁺ to NO ₃ ^? medium (at time 0 h), NO ₃ ^? induced NR synthesis was completely inhibited. The activity of NIR decreased in N-starved cells and the addition of NO ₃ ^? to those cells greatly stimulated NIR activity in the light. The ability to induce NR in darkness was observed when glutamine synthetase activity reached its maximal level during N starvation. Although cells grown in NO ₃ ^? medium exhibited high NR activity, only 0.33% of the total NR was found in intact chloroplasts. We suggest that the ability, to induce NR in darkness is dependent on the level of N starvation, and that NR in D. salina is located in the cytosol. Light seems to play an indirect regulatory role on NO ₃ ^? uptake and NR induction due to the expression of NR and NO ₃ ^? -transporter mRNAs.     

NO 3 − transport across the plasma membrane of Arabidopsis thaliana root hairs: Kinetic control by pH and membrane voltage

High-affinity nitrate transport was examined in intact root hair cells of Arabidopsis thaliana using electrophysiological recordings to characterise the response of the plasma membrane to NO ₃ ^? challenge and to quantify transport activity. The NO ₃ ^? -associated membrane current was determined using a three-electrode voltage clamp to bring membrane voltage under experimental control and to compensate for current dissipation along the longitudinal cell axis. Nitrate transport was evident in the roots of seedlings grown in the absence of a nitrogen source, but only 4–6 days postgermination. In 6-day-old seedlings, additions of 5–100 μm NO ₃ ^? to the bathing medium resulted in membrane depolarizations of 8–43 mV, and membrane voltage (V _m) recovered on washing NO ₃ ^? from the bath. Voltage clamp measurements carried out immediately before and following NO ₃ ^? additions showed that the NO ₃ ^? -evoked depolarizations were the consequence of an inward-directed current that appeared across the entire range of accessible voltages (?300 to +50 mV). Both membrane depolarizations and NO ₃ ^? -evoked currents recorded at the free-running voltage displayed quasi-Michaelian kinetics, with apparent values for K_m of 23 ± 6 and 44 ± 11 μm, respectively and, for the current, a maximum of 5.1 ± 0.9 μA cm^?2. The NO ₃ ^? current showed a pronounced voltage sensitivity within the normal physiological range between ?250 and ?100 mV, as could be demonstrated under voltage clamp, and increasing the bathing pH from 6.1 to 7.4–8.0 reduced the current and the associated membrane depolarizations 3- to 8-fold. Analyses showed a well-defined interaction between the kinetic variables of membrane voltage, pH_o and [NO ₃ ^? ]_o. At a constant pH_o of 6.1, depolarization from ?250 to ?150 mV resulted in an approximate 3-fold reduction in the maximum current but a 10% rise in the apparent affinity for NO ₃ ^? . By contrast, the same depolarization effected an approximate 20% fall in the K_m for transport as a function in [H⁺]_o. These, and additional characteristics of the transport current implicate a carrier cycle in which NO ₃ ^? binding is kinetically isolated from the rate-limiting step of membrane charge transit, and they indicate a charge-coupling stoichiometry of 2(H⁺) per NO ₃ ^? anion transported across the membrane. The results concur with previous studies showing a high-affinity NO ₃ ^? transport system in Arabidopsis that is inducible following a period of nitrogen-limiting growth, but they underline the importance of voltage as a kinetic factor controlling NO ₃ ^? transport at the plant plasma membrane.     

Ammonium nutrition increases water absorption in rice seedlings (Oryza sativa L.) under water stress

Water stress is a primary limitation on plant growth. In previous studies, it has been found that ammonium enhances the tolerance of rice plants to water stress, but how water is related to nitrogen form and water stress remains unknown. To study the effects of nitrogen form (NH ₄ ⁺ , NO ₃ ^? , and a mixture of NH ₄ ⁺ and NO ₃ ^? ) on the growth and water absorption of rice (Oryza sativa L.) seedlings, a hydroponic experiment with water stress, simulated by the addition of polyethylene glycol (PEG, 10% w/v, MW 6000), was conducted in a greenhouse. The results showed that, compared with non-water stress, under water stress, the fresh weight of rice seedlings increased by 14% with NH ₄ ⁺ nutrition, whereas it had decreased by about 20% with either NO ₃ ^? or mixed nitrogen nutrition. No significant difference was found in the transpiration rate of excised shoots or in xylem exudation of excised roots in NH ₄ ⁺ supply between the two water situations, whereas xylem flow decreased by 57% and 24% under water stress in NO ₃ ^? and mixed nutrition, and root hydraulic conductivity decreased by 29% and 54% in plants in NH ₄ ⁺ and NO ₃ ^? nutrition conditions, respectively. Although water absorption ability decreased in both NH ₄ ⁺ and NO ₃ ^? nutrition, aquaporin activity was higher in NH ₄ ⁺ than in NO ₃ ^? nutrition, regardless of water stress. We conclude that NH ₄ ⁺ nutrition can improve water handling in rice seedlings and subsequently enhance their resistance to drought.     

Partitioning of previously-accumulated nitrate to translocation,reduction, and efflux in corn roots

The effect of nitrate uptake, or its absence, on the utilization of nitrate previously accumulated by dark-grown, decpitated maize (Zea mays L., cv. DeKalb XL-45) seedlings was examined. Five-d-old plants that had been pretreated with 50 mM ¹⁴NO ₃ ^? for 20 h were exposed for 8 h to nutrient solutions containing either no nitrate or 50 mM ¹⁵NO ₃ ^? , 98.7 atom % ¹⁵N. The ambient solution, xylem exudate, and plant tissue were analyzed to determine the quantities of previously-accumulated (endogenous) ¹⁴NO ₃ ^? that were translocated to the xylem, lost to the solution, or reduced within the tissue during the 8-h period. Energy was continuously available to the roots from the attached endosperm. In the absence of incoming nitrate, appreciable reduction and translocation of the endogenous ¹⁴NO ₃ ^? occurred, but efflux of ¹⁴NO ₃ ^? to the external solution was minimal. In contrast, during ¹⁵NO ₃ ^? uptake, there was considerable efflux of ¹⁴NO ₃ ^? as well as translocation of ¹⁴NO ₃ ^? to the xylem, but little ¹⁴NO ₃ ^? was reduced. Thus there appeared to be an inverse relationship between ¹⁴NO ₃ ^? efflux and reduction. The data are tentatively interpreted on the basis of a model which envisages (a) two storage locations within roots, one of which primarily supplies nitrate for translocation and the other of which primarily supplies nitrate for outward passage through plasmalemma, and (b) the majority of nitrate reduction as occurring during or immediately following influx across the plasmalemma, with endogenous ¹⁴NO ₃ ^? initially moving outward being recycled inward and thereby being reduced.     

Genetic polymorphisms of blood proteins in the troops of Japanese macaques,Macaca fuscata: IV. Erythrocyte esterase polymorphism inMacaca fuscata

Genetic variation at the locus controlling A₁ band of erythrocyte esterase was found in the Japanese macaque,Macaca fuscata. Existence of four alleles,Es-A ₁ ¹ ,Es-A ₁ ² ,Es-A ₁ ³ , andEs-A ₁ ⁴ , controlling the mobility of the band and codominance relation between them were postulated. A majority of the troops examined were monomorphic inEs-A ₁ 1-1 phenotype, and the variant phenotypes were observed to occur only in Yugawara-Ihama, Arashiyama, and Koshima areas.