Qualitative analysis of a model generating long potential waves in Ba-treated nerve cells—I. Reduced systems

This study is related to a model describing the behavior of barium-treatedAplysia neurons generating regular burst-plateau patterns. The model is represented by an autonomous dynamical system, defined inR ⁴ and depending on a small parameter. This paper is restricted to the qualitative study of three “reduced systems” deduced from the “complete system”. Part of the study is performed with the use of the qualitative theory of singular perturbations. The predicted behaviors are compared with experimental results.     

The reaction force and the transition region of a reaction

The reaction force F(R) and the position-dependent reaction force constant κF(R) are defined by F(R)=-∂V(R)/∂R and κ(R)=∂²V(R)/∂R², where V(R) is the potential energy of a reacting system along a coordinate R. The minima and maxima of F(R) provide a natural division of the process into several regions. Those in which F(R) is increasing are where the most dramatic changes in electronic properties take place, and where the system goes from activated reactants (at the force minimum) to activated products (at the force maximum). κ(R) is negative throughout such a region. We summarize evidence supporting the idea that a reaction should be viewed as going through a transition region rather than through a single point transition state. A similar conclusion has come out of transition state spectroscopy. We describe this region as a chemically-active, or electronically-intensive, stage of the reaction, while the ones that precede and follow it are structurally-intensive. Finally, we briefly address the time dependence of the reaction force and the reaction force constant.     

Model-free model elimination: A new step in the model-free dynamic analysis of NMR relaxation data

Model-free analysis is a technique commonly used within the field of NMR spectroscopy to extract atomic resolution, interpretable dynamic information on multiple timescales from the R ₁, R ₂, and steady state NOE. Model-free approaches employ two disparate areas of data analysis, the discipline of mathematical optimisation, specifically the minimisation of a χ² function, and the statistical field of model selection. By searching through a large number of model-free minimisations, which were setup using synthetic relaxation data whereby the true underlying dynamics is known, certain model-free models have been identified to, at times, fail. This has been characterised as either the internal correlation times, τ _e , τ _f , or τ _s , or the global correlation time parameter, local τ _m , heading towards infinity, the result being that the final parameter values are far from the true values. In a number of cases the minimised χ² value of the failed model is significantly lower than that of all other models and, hence, will be the model which is chosen by model selection techniques. If these models are not removed prior to model selection the final model-free results could be far from the truth. By implementing a series of empirical rules involving inequalities these models can be specifically isolated and removed. Model-free analysis should therefore consist of three distinct steps: model-free minimisation, model-free model elimination, and finally model-free model selection. Failure has also been identified to affect the individual Monte Carlo simulations used within error analysis. Each simulation involves an independent randomised relaxation data set and model-free minimisation, thus simulations suffer from exactly the same types of failure as model-free models. Therefore, to prevent these outliers from causing a significant overestimation of the errors the failed Monte Carlo simulations need to be culled prior to calculating the parameter standard deviations.     

A relational theory of biological systems II

The general Theory of Categories is applied to the study of the (M, R)-systems previously defined. A set of axioms is provided which characterize “abstract (M, R)-systems”, defined in terms of the Theory of Categories. It is shown that the replication of the repair components of these systems may be accounted for in a natural way within this framework, thereby obviating the need for anad hoc postulation of a replication mechanism. A time-lag structure is introduced into these abstract (M, R)-systems. In order to apply this structure to a discussion of the “morphology” of these systems, it is necessary to make certain assumptions which relate the morphology to the time lags. By so doing, a system of abstract biology is in effect constructed. In particular, a formulation of a general Principle of Optimal Design is proposed for these systems. It is shown under what conditions the repair mechanism of the system will be localized into a spherical region, suggestive of the nuclear arrangements in cells. The possibility of placing an abstract (M, R)-system into optimal form in more than one way is then investigated, and a necessary and sufficient condition for this occurrence is obtained. Some further implications of the above assumptions are then discussed.     

EFFECTS OF VARIATION IN INTERCELLULAR ELECTRICAL COUPLING ON SYNAPTIC POTENTIALS IN SMOOTH MUSCLE: A COMPUTATIONAL STUDY

We have computationally explored the effect of quantitative variations in the extent of cell-to-cell electrical coupling on the synaptic potentials generated in smooth muscle. Neuronally produced spontaneous excitatory junction potentials (SEJPs) generated in a cubical “bidomain” model of syncytial tissue were simulated computationally. It was found that SEJP properties vary conspicuously as the principal parameter of interest, the cell–to–cell coupling resistance, R_i, is altered. For example, on increasing R_i, SEJP peak amplitudes at node zero (the node of generation) increase dramatically, while amplitudes at nodes 1 and 2 (which are passively depolarized) become progressively lower fractions of the amplitude of the zeroeth-node SEJP. The time to peak of the SEJPs also increases concomitantly when R_i is elevated. These observations indicate the nature of variations in synaptic potentials that would be expected under conditions of altered intercellular electrical coupling in smooth muscle. We discuss their implications in relation to the physiology of syncytial tissue, and in the context of recent experimental observations made in the presence of a putative inhibitor of cell–to–cell electrical coupling, 1-heptanol.     

Transport of sodium and chloride across earthworm skin in vitro

We present a new invertebrate model for the study of epithelial sodium transport in tight epithelia, the earthworm integument. Dissected segments of earthworm integument were mounted in modified Ussing chambers and perfused with either pond water (PW) or earthworm ringer solution (ERS) on the apical side. In order to investigate ion transport under near-in vivo physiological conditions, measurements were performed under current-clamp conditions by monitoring the transepithelial potential (V _T), as well as the transepithelial resistance (R _T). These were recorded continuously and the virtual short circuit current (I _SC) was calculated. The integument has a high transepithelial resistance (R _T=9,037±502 Ω cm² for PW, n=24, and 11,055±1,320 Ω cm² for ERS, n=32). V _T was −3.7±2.2 mV for PW (n=24) and −1.5±1.0 mV for ERS (n=32), and I _SC was −0.57±0.30 μA/cm² for PW (n=24) and −0.44±0.24 μA/cm² for ERS (n=32). Only under PW, but not under ERS conditions, was there a pronounced inhibition of I _SC by low doses of amiloride or its analogues phenamil and benzamil. The resistance of the paracellular pathway was found to be very high. The terrestrial oligochaete Lumbricus seems especially adapted to the environmental conditions because it has an ultra-tight integument and a very fast up- and down-regulation of apical Na⁺ channels.     

Monoterpenes as novel substrates for oxidation and halo-hydroxylation with chloroperoxidase from Caldariomyces fumago

Chloroperoxidase (CPO) from Caldariomyces fumago was analysed for its ability to oxidize ten different monoterpenes with hydrogen peroxide as oxidant. In the absence of halide ions geraniol and, to a lesser extent, citronellol and nerol were converted into the corresponding aldehydes, whereas terpene hydrocarbons did not serve as substrates under these conditions. In the presence of chloride, bromide and iodide ions, every terpene tested was converted into one or more products. (1S)-(+)-3-carene was chosen as a model substrate for the CPO-catalysed conversion of terpenes in the presence of sodium halides. With chloride, bromide and iodide, the reaction products were the respective (1S,3R,4R,6R)-4-halo-3,7,7-trimethyl-bicyclo[4.1.0]-heptane-3-ols, as identified by ¹H and ¹³C nuclear magnetic resonance. These product formations turned out to be strictly regio- and stereoselective and proceeded very rapidly and almost quantitatively. Initial specific activities of halohydrin formation increased from 4.22 U mg⁻¹ with chloride to 12.22 U mg⁻¹ with bromide and 37.11 U mg⁻¹ with iodide as the respective halide ion. These results represent the first examples of the application of CPO as a highly efficient biocatalyst for monoterpene functionalization. This is a promising strategy for ‘green’ terpene chemistry overcoming drawbacks usually associated with cofactor-dependent oxygenases, whole-cell biocatalysts and conventional chemical methods used for terpene conversions.     

<Emphasis Type="Italic">Shewanella upenei</Emphasis> sp. nov., a lipolytic bacterium isolated from bensasi goatfish <Emphasis Type="Italic">Upeneus bensasi</Emphasis>

A Gram-staining-negative, motile, non-spore-forming and rod-shaped bacterial strain, 20-23R^T, was isolated from intestine of bensasi goatfish, Upeneus bensasi, and its taxonomic position was investigated by using a polyphasic study. Phylogenetic analyses based on 16S rRNA gene sequences revealed that strain 20-23R^T belonged to the genus Shewanella. Strain 20-23R^T exhibited 16S rRNA gene sequence similarity values of 99.5, 99.2, and 97.5% to Shewanella algae ATCC 51192^T, Shewanella haliotis DW01^T, and Shewanella chilikensis JC5^T, respectively. Strain 20-23R^T exhibited 93.1–96.0% 16S rRNA gene sequence similarity to the other Shewanella species. It also exhibited 98.3–98.4% gyrB sequence similarity to the type strains of S. algae and S. haliotis. Strain 20-23R^T contained simultaneously both menaquinones and ubiquinones; the predominant menaquinone was MK-7 and the predominant ubiquinones were Q-8 and Q-7. The fatty acid profiles of strain 20–23R^T, S. algae KCTC 22552^T and S. haliotis KCTC 12896^T were similar; major components were iso-C_15:0, C_16:0, C_16:1 ω7c and/or iso-C_15:0 2-OH and C_17:1 ω8c. The DNA G+C content of strain 20-23R^T was 53.9 mol%. Differential phenotypic properties and genetic distinctiveness of strain 20–23R^T, together with the phylogenetic distinctiveness, revealed that this strain is distinguishable from recognized Shewanella species. On the basis of the data presented, strain 20-23R^T represents a novel species of the genus Shewanella, for which the name Shewanella upenei sp. nov. is proposed. The type strain is 20–23R^T (=KCTC 22806^T =CCUG 58400^T).     

Leaf respiration/photosynthesis relationship and variation: an investigation of 39 woody and herbaceous species in east subtropical China

Thirty-nine plant species including woody and herbaceous species grown in wet and warm subtropical regions were collected and classified into woody and herb functional groups. Net photosynthesis (P _n) and dark respiration (R) were measured at constant 25°C under neither water nor nitrogen limited condition to assess whether the R/P _n ratio was constant across different species and functional groups. Our results suggest that P _n and R were highly skewed among the 39 species, ranging from 5 to 25 and 1 to 5 μmol m⁻² s⁻¹, respectively, while R/P _n ratio was normally distributed at 0.1–0.3. Mean R/P _n ratio was 0.19 for 39 species, and 0.20 and 0.18 for woody and herbs, respectively, showing no significant difference between the two groups. Leaf P _n, R, and R/P _n ratios exhibited large variations across 39 species while R/P _n ratio in our subtropical species was considerably higher than other studies. Our results also indicated that the difference within each group was even larger than between the two groups. Based on the pooled data set at global scale, and considering R/P _n ratios performance under a combination of wet and warm conditions, the mean R/P _n ratio of 0.19 fell between the R/P _n ratio of 0.23 under dry and warm conditions and the R/P _n ratio of 0.07 under cold regardless of the precipitation conditions. The comparison with published data sets indicated significant effects of long-term precipitation and temperature on leaf R/P _n ratios at global scale, and we found that the plants adapting to warm and wet climates including our thirty-nine species tend to have a lower R/P _n ratio.     

Measurement of net ecosystem production and ecosystem respiration in a Zoysia japonica grassland,central Japan,by the chamber method

Measuring light, temperature, soil moisture, and growth provides a better understanding of net ecosystem production (NEP), ecosystem respiration (R _eco), and their response functions. Here, we studied the variations in NEP and R _eco in a grassland dominated by a perennial warm-season C₄ grass, Zoysia japonica. We used the chamber method to measure NEP and R _eco from August to September 2007. Biomass and leaf area index (LAI) were also measured to observe their effects on NEP and R _eco. Diurnal variations in NEP and R _eco were predicted well by light intensity (PPFD) and by soil temperature, respectively. Maximum NEP (NEP_max) values on days of year 221, 233, 247, and 262, were 2.44, 2.55, 3.90, and 4.17 μmol m⁻² s⁻¹, respectively. Throughout the growing period, the apparent quantum yield (α) increased with increasing NEP_max that ranged from 0.0154 to 0.0515, and NEP responded to the soil temperature changes by 44% and R _eco changes by 48%, and R _eco responded from 88 to 94% with the soil temperature diurnally. NEP’s light response and R _eco’s temperature response were affected by soil water content; more than 27% of the variation in NEP and 67% of the variation in R _eco could be explained by this parameter. NEP was strongly correlated with biomass and LAI, but R _eco was not, because environmental variables affected R _eco more strongly than growth parameters. Using the light response of NEP, the temperature response of R _eco, and meteorological data, daily NEP and R _eco were estimated at 0.67, 0.81, 1.17, and 1.56 g C m⁻², and at 2.88, 2.50, 3.51, and 3.04 g C m⁻², respectively, on days of year 221, 233, 247, and 262. The corresponding daily gross primary production (NEP + R _eco) was 3.5, 3.3, 4.6, and 4.6 g C m⁻².     

Nondestructive,simple, and accurate model for estimation of the individual leaf area of som (<Emphasis Type="Italic">Persea bombycina</Emphasis>)

Nondestructive approach of modeling leaf area could be useful for plant growth estimation especially when number of available plants is limited and/or experiment demands repeated estimation of leaf area over a time scale. A total of 1,280 leaves were selected randomly from eight different morphotypes of som (Persea bombycina) established at randomized complete block design under recommended cultural regimes in field. Maximum leaf laminar width (B), length (L) and their squares B², L²; leaf area (LA), and lamina length × width (L×B) were determined over two successive seasons. Leaf parameters were significantly affected by morphotypes; but seasons had nonsignificant impacts on tested features. Therefore, pooled seasonal morphotype means of each parameter were used to establish relationship with LA. L and its square L² did not provide accurate models for LA predictions. Considerably better models were obtained by using B (y = 2.984 + 7.9664 x, R ² = 0.615, P≥0.001, n = 119) and B² (y = 12.784+ 0.9604 x, R ² = 0.605, P≥0.001, n = 119) as independent variables. However, maximum accuracy of prediction of LA could be achieved through a simple linear relationship of L×B (y = 8.2203 + 0.4224 x, R ² = 0.843, P≥0.0001, n = 119). The model (LA:L×B) was validated with randomly selected leaf samples (n = 360) of som morphotypes and highly significant (P≤0.001) linear function was found between actual and predicted LAs. Therefore, the last model may consider adequate to predict leaf area of all cultivars of som with sufficient fidelity.     

Cardiovascular control via angiotensin II and circulating catecholamines in the spiny dogfish, Squalus acanthias

The contributions of circulating angiotensin II (Ang II) and catecholamines to cardiovascular control in the spiny dogfish were investigated by monitoring the effects of exogenous and endogenous dogfish [Asn¹, Pro³, Ile⁵]-Ang II (dfAng II) on plasma catecholamine levels and blood pressure regulation. Bolus intravenous injections of dfAng II (30–1200 pmol kg⁻¹) elicited dose-dependent increases in plasma adrenaline and noradrenaline concentrations, caudal artery pressure (P _CA), and systemic vascular resistance (R _S), and a decrease in cardiac output (Q). Similar injections of Ang II in dogfish pre-treated with the α-adrenoceptor antagonist yohimbine (4 mg kg⁻¹) also elicited dose-dependent increases in plasma catecholamine levels yet the cardiovascular effects were abolished. Dogfish treated with yohimbine were hypotensive and had elevated levels of plasma Ang II and catecholamines. Intravenous injection of the smooth muscle relaxant papaverine (10 mg kg⁻¹) elicited a transient decrease in P _CA and R _S, and increases in plasma Ang II and catecholamine levels. In dogfish first treated with lisinopril (10⁻⁴ mol kg⁻¹), an angiotensin converting enzyme inhibitor, papaverine treatment caused a more prolonged and greater decrease in P _CA and R _S, an attenuated increase in plasma catecholamines, and no change in plasma Ang II. By itself, lisinopril treatment had little effect on P _CA, and no effect on R _S, plasma Ang II or catecholamines. In yohimbine-treated dogfish, papaverine treatment elicited marked decreases in P _CA, R _S, and Q, and increases in plasma Ang II and catecholamines. Among the three papaverine treatments, there was a positive linear relationship between plasma Ang II and catecholamine concentrations, and the cardiovascular and hormonal changes were most pronounced in the yohimbine + papaverine treatment. Therefore, under resting normotensive conditions, while Ang II does not appear to be involved in cardiovascular control, catecholamines play an important role. However, during a hypotensive stress elicited by vascular smooth muscle relaxation, Ang II indirectly contributes to cardiovascular control by dose-dependently stimulating catecholamine release. Accepted: 24 February 1999     

Evaluating HapMap SNP data transferability in a large-scale genotyping project involving 175 cancer-associated genes

One of the many potential uses of the HapMap project is its application to the investigation of complex disease aetiology among a wide range of populations. This study aims to assess the transferability of HapMap SNP data to the Spanish population in the context of cancer research. We have carried out a genotyping study in Spanish subjects involving 175 candidate cancer genes using an indirect gene-based approach and compared results with those for HapMap CEU subjects. Allele frequencies were very consistent between the two samples, with a high positive correlation (R) of 0.91 (P<<1×10⁻⁶). Linkage disequilibrium patterns and block structures across each gene were also very similar, with disequilibrium coefficient (r ²) highly correlated (R=0.95, P<<1×10⁻⁶). We found that of the 21 genes that contained at least one block larger than 60 kb, nine (ATM, ATR, BRCA1, ERCC6, FANCC, RAD17, RAD50, RAD54B and XRCC4) belonged to the GO category “DNA repair”. Haplotype frequencies per gene were also highly correlated (mean R=0.93), as was haplotype diversity (R=0.91, P<<1×10⁻⁶). “Yin yang” haplotypes were observed for 43% of the genes analysed and 18% of those were identical to the ancestral haplotype (identified in Chimpazee). Finally, the portability of tagSNPs identified in the HapMap CEU data using pairwise r ² thresholds of 0.8 and 0.5 was assessed by applying these to the Spanish and current HapMap data for 66 genes. In general, the HapMap tagSNPs performed very well. Our results show generally high concordance with HapMap data in allele frequencies and haplotype distributions and confirm the applicability of HapMap SNP data to the study of complex diseases among the Spanish population. Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Segmental expression of claudin proteins correlates with tight junction barrier properties in rat intestine

In tubular epithelia, barrier function varies in a segment-specific way. The aim of this study was to correlate the presence of tight junction proteins and paracellular barrier properties along rat intestine. Tissue segments of duodenum, jejunum, ileum, and colon were stripped of submucosal cell layers and mounted in Ussing chambers for impedance spectroscopy to measure epithelial resistance (R ^epi). In parallel, expression of tight junction proteins was analysed by Western blots and immune fluorescence confocal microscopy. Colon showed highest R ^epi, followed by duodenum, jejunum, and ileum. In small intestine, common transepithelial resistance (R ^trans or TER) overestimated true R ^epi by ~60%. In colon, strongest expression of “tightening” claudins 1, 3, 4, 5, and 8 was detected. In accordance with R ^epi the most proximal of the small intestinal segments, duodenum exhibited highest expression of “tightening” claudins and lowest expression of claudins mediating permeability, namely claudin-2, -7, and -12, compared to jejunum and ileum. These results correspond to the specific role of the duodenum as the first segment facing the acidic gastric content.     

Diffusion regulated growth characteristics of a spherical prevascular carcinoma

Recently a mathematical model of the prevascular phases of tumor growth by diffusion has been investigated (S. A. Maggelakis and J. A. Adam,Math. Comput. Modeling, in press). In this paper we examine in detail the results and implications of that mathematical model, particularly in the light of recent experimental work carried out on multicellular spheroids. The overall growth characteristics are determined in the present model by four parameters:Q, γ, b, andδ, which depend on information about inhibitor production rates, oxygen consumption rates, volume loss and cell proliferation rates, and measures of the degree of non-uniformity of the various diffusion processes that take place. The integro-differential growth equation is solved for the outer spheroid radiusR ₀(t) and three related inner radii subject to the solution of the governing time-independent diffusion equations (under conditions of diffusive equilibrium) and the appropriate boundary conditions. Hopefully, future experimental work will enable reasonable bounds to be placed on parameter values referred to in this model: meanwhile, specific experimentally-provided initial data can be used to predict subsequent growth characteristics ofin vitro multicellular spheroids. This will be one objective of future studies.     

Isolation and characterization of highly (R)-specific N-acetyl-1-phenylethylamine amidohydrolase, a new enzyme from Arthrobacter aurescens AcR5b

A new amidohydrolase deacetylating several N-acetyl-1-phenylethylamine derivatives (R)-specifically was found in Arthrobacter aurescens AcR5b. The strain was isolated from a wet haystack by enrichment culture with (R)-N-acetyl-1-phenylethylamine as the sole carbon source. (R) and (S )-N-acetyl-1-phenylethylamine do not serve as inducers for acylase formation. By improving the growth conditions the enzyme production was increased 47-fold. The amidohydrolase was purified to homogeneity leading to a 5.2-fold increase of the specific activity with a recovery of 67%. A molecular mass of 220 kDa was estimated by gel filtration. Sodium dodecyl sulfate/polyacrylamide gel electrophorosis shows two subunits with molecular masses of 16 kDa and 89 kDa. The optimum pH and temperature were pH 8 and 50 °C, respectively. The enzyme was stable in the range of pH 7–9 and at temperatures up to 30 °C. The enzyme activity was inhibited by Cu²⁺, Co²⁺, Ni²⁺, and Zn²⁺, and this inhibition was reversed by EDTA.M Received: 20 September 1996 / Received version: 23 December 1996 / Accepted: 30 December 1996     

Frequency switching in a two-compartmental model of the dopaminergic neuron

Mid-brain dopaminergic (DA) neurons display two functionally distinct modes of electrical activity: low- and high-frequency firing. The high-frequency firing is linked to important behavioral events in vivo. However, it cannot be elicited by standard manipulations in vitro. We had suggested a two-compartmental model of the DA cell that united data on firing frequencies under different experimental conditions. We now analyze dynamics of this model. The analysis was possible due to introduction of timescale separation among variables. We formulate the requirements for low and high frequencies. We found that the modulation of the SK current gating controls the frequency rise under applied depolarization. This provides a new mechanism that limits the frequency in the control conditions and allows high-frequency responses to depolarization if the SK current gating is downregulated. The mechanism is based on changing Ca^2 + balance and can also be achieved by direct modulation of the balance. Interestingly, such changes do not affect the high-frequency oscillations under NMDA. Therefore, altering Ca^2 + balance allows combining the high-frequency response to NMDA activation with the inability of other treatments to effectively elevate the frequency. We conclude that manipulations affecting Ca^2 + balance are most effective in controlling the frequency range. This modeling prediction gives a clue to the mechanism of the high-frequency firing in the DA neuron in vivo and in vitro.     

“Chelatable iron pool”: inositol 1,2,3-trisphosphate fulfils the conditions required to be a safe cellular iron ligand

Mammalian cells contain a pool of iron that is not strongly bound to proteins, which can be detected with fluorescent chelating probes. The cellular ligands of this biologically important “chelatable”, “labile” or “transit” iron are not known. Proposed ligands are problematic, because they are saturated by magnesium under cellular conditions and/or because they are not “safe”, i.e. they allow iron to catalyse hydroxyl radical formation. Among small cellular molecules, certain inositol phosphates (InsPs) excel at complexing Fe³⁺ in such a “safe” manner in vitro. However, we previously calculated that the most abundant InsP, inositol hexakisphosphate, cannot interact with Fe³⁺ in the presence of cellular concentrations of Mg²⁺. In this work, we study the metal complexation behaviour of inositol 1,2,3-trisphosphate [Ins(1,2,3)P ₃], a cellular constituent of unknown function and the simplest InsP to display high-affinity, “safe”, iron complexation. We report thermodynamic constants for the interaction of Ins(1,2,3)P ₃ with Na⁺, K⁺, Mg²⁺, Ca²⁺, Cu²⁺, Fe²⁺ and Fe³⁺. Our calculations indicate that Ins(1,2,3)P ₃ can be expected to complex all available Fe³⁺ in a quantitative, 1:1 reaction, both in cytosol/nucleus and in acidic compartments, in which an important labile iron subpool is thought to exist. In addition, we calculate that the fluorescent iron probe calcein would strip Fe³⁺ from Ins(1,2,3)P ₃ under cellular conditions, and hence labile iron detected using this probe may include iron bound to Ins(1,2,3)P ₃. Therefore Ins(1,2,3)P ₃ is the first viable proposal for a transit iron ligand. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Existence of traveling wave solutions in a diffusive predator-prey model

 We establish the existence of traveling front solutions and small amplitude traveling wave train solutions for a reaction-diffusion system based on a predator-prey model with Holling type-II functional response. The traveling front solutions are equivalent to heteroclinic orbits in R ⁴ and the small amplitude traveling wave train solutions are equivalent to small amplitude periodic orbits in R ⁴ . The methods used to prove the results are the shooting argument and the Hopf bifurcation theorem. Received: 25 May 2001 / Revised version: 5 August 2002 / Published online: 19 November 2002 RID="*" ID="*" Research was supported by the National Natural Science Foundations (NNSF) of China. RID="*" ID="*" Research was partially supported by the Natural Sciences and Engineering Research Council (NSERC) of Canada. On leave from the Department of Mathematics and Statistics, Dalhousie University, Halifax, Nova Scotia B3H 3J5, Canada. Mathematics Subject Classification (2000): 34C35, 35K57 Key words or phrases: Traveling wave solution – Wazewski set – Shooting argument – Hopf bifurcation Acknowledgements. We would like to thank the two referees for their careful reading and helpful comments.     

Enantioselective biocatalytic hydrolysis of (<Emphasis Type="Italic">R</Emphasis>,<Emphasis Type="Italic">S</Emphasis>)-mandelonitrile for production of (<Emphasis Type="Italic">R</Emphasis>)-(−)-mandelic acid by a newly isolated mutant strain

(R)-(−)-Mandelic acid (R-MA) is an important intermediate with broad uses. Recently, R-MA production using nitrilase has been gaining more and more attention due to its higher productivity and enantioselectivity. In this work, a new bacterium WT10, which exhibited favorable nitrilase activity and excellent enantioselectivity for production of R-MA by enantioselective biocatalytic hydrolysis of (R,S)-mandelonitrile, was isolated and identified as a strain of Alcaligenes faecalis. In order to improve its nitrilase activity for industrial application, the wild-type strain WT10 was further subjected to mutagenesis using a combined LiCl–ultraviolet irradiation and low energy N⁺ ion beams implantation technique. A valuable mutant strain A. faecalis ZJUTB10 was obtained. The nitrilase specific activity of the mutant strain was greatly improved up to 350.8 U g⁻¹, in comparison with wild-type strain WT10 of 53.09 U g⁻¹. The reaction conditions for R-MA production by mutant strain A. faecalis ZJUTB10 were also optimized. Nitrilase activity in mutant strain showed a broad pH optimum at pH 7.7–8.5. The optimal temperature was 35°C. The highest production rate reached 9.3 mmol h⁻¹ g⁻¹. The results showed that mutant strain A. faecalis ZJUTB10 was a new candidate for efficient R-MA production from (R,S)-mandelonitrile and could potentially be used in industrial production.