Estimation of denitrification potential in a karst aquifer using the <Superscript>15</Superscript>N and <Superscript>18</Superscript>O isotopes of NO<Stack><Subscript>3</Subscript><Superscript>−</Superscript></Stack>

A confined aquifer in the Malm Karst of the Franconian Alb, South Germany was investigated in order to understand the role of the vadose zone in denitrifiaction processes. The concentrations of chemical tracers Sr²⁺ and Cl^– and concentrations of stable isotope ¹⁸O were measured in spring water and precipitation during storm events. Based on these measurements a conceptual model for runoff was constructed. The results indicate that pre-event water, already stored in the system at the beginning of the event, flows downslope on vertical and lateral preferential flow paths. Chemical tracers used in a mixing model for hydrograph separation have shown that the pre-event water contribution is up to 30%. Applying this information to a conceptual runoff generation model, the values of ¹⁵N and ¹⁸O in nitrate could be calculated. Field observations showed the occurence of significant microbial denitrification processes above the soil/bedrock interface before nitrate percolates through to the deeper horizon of the vadose zone. The source of nitrate could be determined and denitrification processes were calculated. Assuming that the nitrate reduction follows a Rayleigh process one could approximate a nitrate input concentration of about 170 mg/l and a residual nitrate concentration of only about 15%. The results of the chemical and isotopic tracers postulate fertilizers as nitrate source with some influence of atmospheric nitrate. The combined application of hydrograph separation and determination of isotope values in ¹⁵N and ¹⁸O of nitrate lead to an improved understanding of microbial processes (nitrification, denitrification) in dynamic systems.     

Determination of the lifetime of D<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack> and HD<Superscript>−</Superscript> ions

A method for determining the lifetime of unstable ions is described. The method is based on measuring the decrease in the ion beam current onto a fixed detector with increasing path length of the ion beam from the ion source to the detector. The measurements performed for D^? ₂ and HD^? molecular ions have shown that their lifetimes are 3.5 ± 0.1 and 4.4 ± 0.1 μs, respectively.     

Synthesis of two-dimensional human walking: a test of the <Emphasis Type="Italic">λ</Emphasis>-model

To test the -model version of the equilibrium point hypothesis both for feasibility and validity with respect to the control of terrestrial locomotion, we developed a two-dimensional, eleven-segment musculoskeletal model of the human body including 14 muscle-tendon complexes per leg, three-segment feet, and a physiologically based model of foot-ground interaction. Human walking was synthesized by numerical integration of the coupled muscle-tendon and rigid body dynamics. To this end a control algorithm based on the -model was implemented in the model providing muscle stimulation patterns that guaranteed dynamically stable walking including a balanced trunk. Thus, the timing of the movement is not preset by a central pattern generator but emerges from the interaction of the musculoskeletal system with the control algorithm. The control parameters were found in a trial-and-error approach. The feedforward part of the control scheme consists of just two target configurations each of which is composed of a set of one nominal length per muscle (-model). Variation of gravity reveals that (1) the synthesized walking patterns are close to ballistic walking and (2) this muscularly induced natural walking can only be initiated and maintained in the range between about a tenth and three times earth-bound gravity. Our walking patterns are robust both against parameter variations and shuffling of the swing leg. We discuss our model with respect to gravity scaling, speed control, feedback delay, and the terms equilibrium point hypothesis and central pattern generator.     

Assessing the Efficiency of the Ability to Intentionally Variate the Power of β<Subscript>2</Subscript> Frequencies in the Frontal Lobes of the Cerebral Cortex

We performed longitudinal examinations by neurofeedback in 17 subjects. The subjects were trained for 12 training seßsions (three weeks) to voluntarily increase the intensity of the ß₂ frequencies in the frontal EEG electrodes of the right (the D scenario) and the left (the S scenario) hemispheres. All the subjects were divided into three groups depending on the training efficacy: a group of subjects that successfully controlled the ß activity in the frontal electrodes of both hemispheres (nine subjects), a group of subjects that successfully controlled this activity only in the right hemisphere (four subjects), and a group of subjects that failed to train during the specified period (four subjects). Analysis of the obtained data showed that the training efficacy depended on the cognitive activity that was focused on achieving the corresponding EEG effects and on the individual personality characteristics.     

Presence of Ornithine in the Urate-binding α<Subscript>1</Subscript>—<Subscript>2</Subscript>Globulin

THE urate-binding α₁–α₂ globulin has been isolated from human plasma in a highly purified state¹. The protein was purified by DEAE-‘Sephadex’, ammonium sulphate precipitation and semi-preparative Polyacrylamide gel electrophoresis. The urate-binding α₁–α₂ globulin is a rod-shaped glycoprotein, containing 12.1% carbohydrate, with an isoelectric point of 4.6 and a molecular weight of 67,000 ± 4,000. Amino-acid analysis indicated an unknown basic compound which appeared as an extra peak just in front of lysine¹. To identify this compound, high voltage paper electrophoresis has been carried out on a plate electrophoresis apparatus in pyridine-acetate buffer pH 3.5. A spot separated out corresponding to ornithine. Amino-acid analysis on a BC-200 automatic analyser (Bio-Cal Instruments Co., West Germany), with a 54 cm column at 55° C and with 0.35 M sodium citrate buffer, pH 5.28, as elution buffer at a flow-rate of 150 ml./h, showed that ornithine was present. The presence of ornithine in the protein hydrolysate was also verified by gas chromatography/mass spectrometry².     

A computer-aided quantum chemical study of the N<Stack><Subscript>15</Subscript><Superscript>−</Superscript></Stack> cluster

Ab initio (RHF, MP2) and Density Functional Theory (DFT) methods have been used to examine six isomers of the N15m cluster with the 6-31+G* basis set. Different from the known odd-numbered anionic N7m, N9m, and N11m clusters, in which the open-chain structures are the most stable species, the most stable N15m isomer is structure 1 (C1), which may be considered as a complex between the fragments cyclic N5m (D5h) and staggered N10 (D2d). The decomposition pathways of structure 2 (CS), containing two aromatic N5 rings connected by a N5 chain, and the open-chain structure 3 (C2v) were studied at the B3LYP/6-31+G* level of theory. Relative energies were refined at the level of B3LYP/6-311+G(3df,2p)//B3LYP/6-31+G*+ZPE (B3LYP/6-31+G*). The barriers for N2 and N5m (D5h) fission reactions for structure 2 are predicted to be 18.2 and 14.2 kcal x mol(-1), respectively. The corresponding N2+N3m fission barrier for structure 3 is predicted to be 11.2 kcal x mol(-1). Supplementary material is available for this article if you access the article at http://dx.doi.org/10.1007/s00894-003-0118-0. A link in the frame on the left on that page takes you directly to the supplementary material. Figure Structure 1 of the N15m cluster, showing bond distances in A and bond angles in degrees     

H<Superscript>−</Superscript> ion density in the plasma of a low-voltage cesium-hydrogen discharge as a function of the cathode emission current

It was shown theoretically that the increase in the cathode emission current in a low-voltage cesium-hydrogen discharge to ≈10 A/cm² leads to an increase in the electron temperature in the anode plasma to T _e ≥ 1 eV. In this regime, the rate constant for the production of H^? ions via dissociative electron attachment to vibrationally excited H₂ molecules is close to its maximum value and the density of H^? ions is maximal (about 10¹³ cm^?3) in the anode plasma.     

α<Subscript>1</Subscript>-Thymosin, α<Subscript>2</Subscript>-interferon,and the LKEKK syntetic peptide inhibit the binding of the B subunit of the cholera toxin to intestinal epithelial cell membranes

The ¹²⁵I-labeled B-subunit of the cholera toxin ([125I]CT-B, specific activity of 98 Ci/mmol) was prepared. This subunit was shown to be bound to the membranes which were isolated from epithelial cells of a mucous tunic of the rat thin intestine with high affinity (K _d = 3.7 nM). The binding of the labeled protein was inhibited by the unlabeled α₂-interferon (IFN-α₂), α₁-thymosin, (TM-α₁), and the LKEKK synthetic peptide corresponding to the 16–20 sequence of TM-α₁ and the 131–135 sequence of human IFN-α₂ (Ki 1.0, 1.5, and 2.0 nM, respectively), whereas the KKEKL unlabeled synthetic peptide did not inhibit the binding (K _i > 100 μМ). The LKEKK peptide and CT-B were shown to dose-dependently increase an activity of the soluble guanylate cyclase (sGC) in the concentration range from 10 to 1000 nM. Thus, the binding of TM- α₁, IFN-α₂, and the LKEKK peptide to the CT-B receptor on a surface of the epithelial cells of the mucous tunic of the rat thin intestine resulted in an increase in the intracellular level of cGMP.     

Protease-catalyzed synthesis of the tripeptide CCK<Subscript>26–28</Subscript>, a fragment of CCK-8

Summary. Two enzymatically synthetic strategies of the tripeptide derivative PhAc-Asp(OMe)-Tyr-Met-OAl are reported. The second strategy gains the advantage of more economical starting materials, less reaction steps and a higher overall isolated yield of this tripeptide fragment over the first strategy. The effect of the acyl-donor ester concentration and structure, the C-α protecting group of the nucleophile, reaction media, enzyme and the carrier on the tripeptide derivative synthesis were studied. This tripeptide selected is a fragment of the cholecystokinin C-terminal octapeptide (CCK-8), a potential therapeutic agent in the control of gastrointestinal function and also a drug candidate for the treatment of epilepsy.     

The effect of metal ions on the binding of ethanol to human alcohol dehydrogenase β<Subscript>2</Subscript>β<Subscript>2</Subscript>

Molecular docking simulations were performed in this study to investigate the importance of both structural and catalytic zinc ions in the human alcohol dehydrogenase beta(2)beta(2) on substrate binding. The structural zinc ion is not only important in maintaining the structural integrity of the enzyme, but also plays an important role in determining substrate binding. The replacement of the catalytic zinc ion or both catalytic and structural zinc ions with Cu(2+) results in better substrate binding affinity than with the wild-type enzyme. The width of the bottleneck formed by L116 and V294 in the substrate binding pocket plays an important role for substrate entrance. In addition, unfavorable contacts between the substrate and T48 and F93 prevent the substrate from moving too close to the metal ion. The optimal binding position occurs between 1.9 and 2.4 A from the catalytic metal ion.     

The neural γ<Subscript>2</Subscript>α<Subscript>1</Subscript>β<Subscript>2</Subscript>α<Subscript>1</Subscript>β<Subscript>2</Subscript> gamma amino butyric acid ion channel receptor: structural analysis of the effects of the ivermectin molecule and disulfide bridges

While ~30% of the human genome encodes membrane proteins, only a handful of structures of membrane proteins have been resolved to high resolution. Here, we studied the structure of a member of the Cys-loop ligand gated ion channel protein superfamily of receptors, human type A γ₂α₁β₂α₁β₂ gamma amino butyric acid receptor complex in a lipid bilayer environment. Studying the correlation between the structure and function of the gamma amino butyric acid receptor may enhance our understanding of the molecular basis of ion channel dysfunctions linked with epilepsy, ataxia, migraine, schizophrenia and other neurodegenerative diseases. The structure of human γ₂α₁β₂α₁β₂ has been modeled based on the X-ray structure of the Caenorhabditis elegans glutamate-gated chloride channel via homology modeling. The template provided the first inhibitory channel structure for the Cys-loop superfamily of ligand-gated ion channels. The only available template structure before this glutamate-gated chloride channel was a cation selective channel which had very low sequence identity with gamma aminobutyric acid receptor. Here, our aim was to study the effect of structural corrections originating from modeling on a more reliable template structure. The homology model was analyzed for structural properties via a 100 ns molecular dynamics (MD) study. Due to the structural shifts and the removal of an open channel potentiator molecule, ivermectin, from the template structure, helical packing changes were observed in the transmembrane segment. Namely removal of ivermectin molecule caused a closure around the Leu 9 position along the ion channel. In terms of the structural shifts, there are three potential disulfide bridges between the M1 and M3 helices of the γ₂ and 2 α₁ subunits in the model. The effect of these disulfide bridges was investigated via monitoring the differences in root mean square fluctuations (RMSF) of individual amino acids and principal component analysis of the MD trajectory of the two homology models—one with the disulfide bridge and one with protonated Cys residues. In all subunit types, RMSF of the transmembrane domain helices are reduced in the presence of disulfide bridges. Additionally, loop A, loop F and loop C fluctuations were affected in the extracellular domain. In cross-correlation analysis of the trajectory, the two model structures displayed different coupling in between the M2–M3 linker region, protruding from the membrane, and the β1-β2/D loop and cys-loop regions in the extracellular domain. Correlations of the C loop, which collapses directly over the bound ligand molecule, were also affected by differences in the packing of transmembrane helices. Finally, more localized correlations were observed in the transmembrane helices when disulfide bridges were present in the model. The differences observed in this study suggest that dynamic coupling at the interface of extracellular and ion channel domains differs from the coupling introduced by disulfide bridges in the transmembrane region. We hope that this hypothesis will be tested experimentally in the near future.     

Sequence specific <Superscript>1</Superscript>H, <Superscript>13</Superscript>C and <Superscript>15</Superscript>N resonance assignments of a cataract-related variant G57W of human γS-crystallin

γS-crystallin is a major structural component of the human eye lens, which maintains its stability over the lifetime of an organism with negligible turnover. The G57W mutant of human γS-crystallin (abbreviated hereafter as γS-G57W) is associated with dominant congenital cataracts. In order to provide a structural basis for the ability of γS-G57W causing cataract, we have cloned, overexpressed, isolated and purified the protein. The 2D [¹⁵N–¹H]-HSQC spectrum recorded with uniformly ¹³C/¹⁵N-labelled γS-G57W was highly dispersed indicating the protein to adopt an ordered conformation. In this paper, we report almost complete sequence-specific ¹H, ¹³C and ¹⁵N resonance assignments of γS-G57W using a suite of heteronuclear 3D NMR experiments.     

Beginning a new Period celebrating the 60<Superscript>th</Superscript> anniversary of the journal <Emphasis Type="Italic">Scientia Sinica—(Science China)</Emphasis>

Funded by the Chinese Academy of Sciences,Science in China (Scientia Sinica) was first published in 1950 and will celebrate its 60th anniversary in 2010. During its earlier     

An optical material for the detection of trace S<Subscript>2</Subscript>O<Subscript>3</Subscript><Superscript>2−</Superscript> in milk based on a copper complex

A novel S₂O₃ ^2? luminescent sensor (Cu²⁺-p-CPIP) was developed and the presence of S₂O₃ ^2? caused an obvious fluorescence enhancement at 420 nm upon excitation at 330 nm, which could be distinguished with the naked eye under a UV lamp. Remarkably, the compound exhibited excellent selective and sensitive response to S₂O₃ ^2? over other common anions with a micromolar limit of detection (0.442 μM) in DMSO/H₂O (v/v, 1:1) buffer. The absorbance intensity and the color of Cu²⁺-p -CPIP solution changed gradually with the increase of S₂O₃ ^2? concentration. The proposed method was applied to the determination of S₂O₃ ^2? in milk samples and the recoveries were 97.5–105%. The preparation of Cu²⁺-p -CPIP exhibited the quick, simple and facile advantages. The results showed that Cu²⁺-p -CPIP can be a good candidate for simple, rapid and sensitive colorimetric detection of S₂O₃ ^2? in aqueous solution.     

Accuracy of the StressEraser<Superscript>®</Superscript> in the Detection of Cardiac Rhythms

StressEraser is a commercially marketed biofeedback device designed to enhance heart rate variability. StressEraser makes its internal calculations on beat-to-beat measures of finger pulse intervals. However, the accuracy and precision of StressEraser in quantifying interbeat intervals using finger pulse intervals has not been evaluated against standard laboratory equipment using R-R intervals. Accuracy was assessed by simultaneously recording interbeat intervals using StressEraser and a standard laboratory ECG system. The interbeat intervals were highly correlated between the systems. The average deviation in interbeat interval recordings between the systems was approximately 6 ms. Moreover, correlations approached unity between the systems on estimates of heart period, heart rate, and heart rate variability. Feedback from StressEraser is based on an interbeat time series that provides sufficient information to provide an excellent estimate of the dynamic changes in heart rate and heart rate variability. The slight variations between StressEraser and the laboratory equipment in quantifying heart rate and heart rate variability are due to features related to monitoring heart rate with finger pulse: (1) a lack in precision in the peak of the finger pulse relative to the clearly defined inflection point in the R-wave, and (2) contribution of variations in pulse transit time.     

Modulation of the conductance of a 2,2′-bipyridine-functionalized peptidic ion channel by Ni<Superscript>2+</Superscript>

An alpha-helical amphipathic peptide with the sequence H2N-(LSSLLSL)3-CONH2 was obtained by solid phase synthesis and a 2,2'-bipyridine was coupled to its N-terminus, which allows complexation of Ni2+. Complexation of the 2,2'-bipyridine residues was proven by UV/Vis spectroscopy. The peptide helices were inserted into lipid bilayers (nano black lipid membranes, nano-BLMs) that suspend the pores of porous alumina substrates with a pore diameter of 60 nm by applying a potential difference. From single channel recordings, we were able to distinguish four distinct conductance states, which we attribute to an increasing number of peptide helices participating in the conducting helix bundle. Addition of Ni2+ in micromolar concentrations altered the conductance behaviour of the formed ion channels in nano-BLMs considerably. The first two conductance states appear much more prominent demonstrating that the complexation of bipyridine by Ni2+ results in a considerable confinement of the observed multiple conductance states. However, the conductance levels were independent of the presence of Ni2+. Moreover, from a detailed analysis of the open lifetimes of the channels, we conclude that the complexation of Ni2+ diminishes the frequency of channel events with larger open times.