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High Salt Concentration (high + salt_concentration)
Selected AbstractsBacillus pumilus SG2 isolated from saline conditions produces and secretes two chitinasesJOURNAL OF APPLIED MICROBIOLOGY, Issue 4 2007G. Ahmadian Abstract Aims: Isolation and characterization of chitinases from a halotolerant Bacillus pumilus. Methods and Results: Bacillus pumilus strain SG2 was isolated from saline conditions. It is able to produce chitinase activity at high salt concentration. SDS-PAGE analysis of the B. pumilus SG2 culture supernatant showed two major bands that were induced by chitin. The amino acid sequence of the two proteins, designated ChiS and ChiL, showed a high homology with the chitinase of B. subtilis CHU26, and chitinase A of B. licheniformis, respectively. N -terminal signal peptide of both proteins was also determined. The molecular weight and isoelectric point of the chitinases were determined to be 63 and 74 kDa, and 4·5 and 5·1, for ChiS and ChiL respectively. The genes encoding for both chitinases were isolated and their sequence determined. The regulation of the chitinase genes is under the control of the catabolite repression system. Conclusions: Secreted chitinase genes and their flanking region on the genome of B. pumilus SG2 have been identified and sequenced. Significance and Impact of the Study: This is the first report of a multiple chitinases-producing B. pumilus halotolerant strain. We have identified two chitinases by using a reverse genetics approach. The chitinases show resistance to salt. [source] Influence of temperature and salinity on the germination of Lotus creticus (L.) from the arid land of TunisiaAFRICAN JOURNAL OF ECOLOGY, Issue 2 2010Mokhtar Rejili Abstract Effects of salinity, temperature and their interactions on the rate and final percentage of germination were evaluated for two populations (Msarref, Oued dkouk) of the invasive glycophyte Lotus creticus Linné, grown under arid environmental conditions of the Tunisia. Seeds that were not treated with NaCl germinated well in a wide range of temperatures. For both populations, maximum germination occurred in distilled water at 25°C and lowest germination for all salinities was at 35°C. Germination was substantially delayed and significantly reduced with an increase in NaCl to levels above 300 mm. Compared to the Oued dkouk population, final germination and germination rate of the Msarref population was completely inhibited at 300 mm NaCl. The interactive effect of temperature and NaCl concentration on final germination and germination rate was significant (P < 0.01), indicating that the germination response to salinity depended on temperature. The inhibition of Oued dkouk population seed germination at high salt concentration was mostly due to osmotic effects while ionic effects were noted at Msarref population. The germination behaviour of the Oued dkouk population would therefore imply adaptive mechanisms to saline environments, while in the Msarref population such mechanisms seem to be absent. Since seed germination is more sensitive to salinity stress than the growth of established plants, the greater tolerance to salinity of Oued dkouk population would be an adaptive feature of this population to saline environment. Résumé L'effet de l'interaction de la salinité et de la température sur la germination de deux populations (Msarref et Oued Dkouk) du lotier de crête (Lotus creticus L.), glycophyte poussant dans des conditions environnementales arides en Tunisie, est étudié. Chez les deux populations, le taux de germination le plus élevé est obtenu à 25°C et le plus faible à 35°C. A 300 mm de NaCl, la germination de la population d'Oued Dkouk est ralentie alors que celle de Msarref est complètement inhibée. L'effet de l'interaction de deux stress est hautement significatif (P < 0,01). Il semble, ainsi, que l'effet de chacun de deux stress est intensifié par l'autre. Cependant, les deux populations montrent un comportement halophytique différent. L'inhibition de la germination, par la salinité, chez Oued Dkouk est due à un effet osmotique alors que chez Mserref, il est ionique. Il en résulte que la population de oued Dkouk présente une capacité adaptative à l'aridité plus importante que celle observée chez la population Msarref. [source] Effect of lipid oxidation and frozen storage on muscle proteins of Atlantic mackerel (Scomber scombrus)JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 5 2002Suhur Saeed Abstract The effect of storage on the lipids and proteins in Atlantic mackerel stored for up to 24 months at ,20 and ,30,°C was studied. Traditional methods including the peroxide value, thiobarbituric acid-reactive substances (TBARS) and a reverse phase HPLC method were used to determine the primary and secondary lipid oxidation products. All tests showed an increase in lipid oxidation products with storage time and at a higher storage temperature of ,20,°C compared with samples stored at ,30,°C. Antioxidants had a significant effect (P,<,0.01) on the inhibition of lipid oxidation, as shown by the reduction in peroxide value and hydroxides, and malondialdehyde formation. Similarly, deterioration of protein structure and functionality in mackerel stored for 3, 6, 12 and 24 months was greater at ,20 than ,30,°C. ATPase activity in the myosin extract of Atlantic mackerel showed a significant decrease (P,<,0.01) with progressive frozen storage. Protein solubility in high salt concentration (0.6,M NaCl) decreased (P,<,0.01) during storage at both ,20 and ,30,°C but was greater at ,20,°C. Interestingly, antioxidants BHT, vitamin C and vitamin E protected the proteins against complete loss of ATPase activity and protein solubility to a significant level (P,<,0.01) for up to 1 year at ,20,°C compared with samples stored without antioxidants. This study confirms the deleterious effect of lipid oxidation products on protein structure and function in frozen fatty fish. © 2002 Society of Chemical Industry [source] Phenotypic characteristics of rhizobia isolates nodulating Acacia species in the arid and Saharan regions of MoroccoLETTERS IN APPLIED MICROBIOLOGY, Issue 5 2000K. Zerhari The phenotypic characteristics of 48 isolates obtained from root nodules of four Acacia species (Acacia cyanophylla, A. gummifera, A. horrida and A. raddiana) growing in soils collected from the arid and Saharan regions of Morocco were studied. The rhizobia were very diverse with respect to their cross-nodulation patterns, as well as their physiological and biochemical properties. Dendrograms obtained through computer numerical analysis of 52 phenotypic characteristics showed that isolates could fit into four clusters below the boundary level of 0·85 average distance and that they were very distinct from the reference strains. Some interesting isolates for inoculation trials have been identified. They were able to grow at pH ranging from 4 to 9, tolerate a high salt concentration (3% NaCl) and grew at a maximum temperature between 35 and 40 °C. [source] The Effect of Fruit Age on Seed Germinability of a Heterocarpic Species, Atriplex sagittataPLANT BIOLOGY, Issue 6 2004B. Mandák Abstract: Atriplex sagittata is an annual heterocarpic plant that produces three different fruit types (termed A, B, and C). To examine the consequence of heterocarpy on germinability patterns over long time periods, we compared seed germinability of different fruit types that had been stored for up to 8 years. While germinability of non-dormant type C fruits in distilled water was high (up to 100 %) in the first 2 years, it rapidly decreased over time. Dormant fruit types A and B showed increased germinability up to 7 years, though loss of germinability was lower for type B than for type A fruits. Eight-year-old fruits of all types had significantly lower germinability than younger fruits, probably due to loss of viability. Heterocarpy, therefore, ensures that emergence rates for seedlings of A. sagittata will be maintained over relatively long periods, even in years of strong disturbance when all adult plants may be destroyed. The experiment further showed that germinability of all fruit types in high concentrations of salt, as compared with water treatment, changed over the course of 8 years. Whilst dormant types (A and B) of A. sagittata show increased germinability with age of the seed in water treatment, they significantly lose germinability over time with salinity treatment. Type C fruit was not influenced by salt in the first year, but germinability rapidly decreased with time. It follows that the species is able to germinate under high salt concentration in the first year, but this advantage gradually disappears. [source] Positive ion electrospray ionization mass spectrometry of double-stranded DNA/drug complexesRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 24 2001Rajesh Gupta An Erratum has been published for this article in Rapid Communicatons in Mass Spectrometry 16(7) 2002,740,741. Positive ion electrospray ionization mass spectra of 16 base-pair double-stranded (ds)DNA have been obtained with essentially no ions from single-stranded DNA present. Single-stranded DNA was minimized by: (1) careful choice of DNA sequences; (2) the use of a relatively high salt concentration (0.1,M ammonium acetate, pH 8.5), and, (3) a low desolvation temperature (40,°C). Similarly, ESI-MS complexes of dsDNA with cisplatin, daunomycin and distamycin were obtained that contained only negligible amounts of single-stranded DNA. The complexes with daunomycin and distamycin were more stable to strand separation in the gas phase than dsDNA alone. This is in agreement with solution studies and with other recent gas phase results. These data contrast with many earlier ESI-MS studies of dsDNA and DNA/drug complexes in which ions from ssDNA are also normally observed. Copyright © 2001 John Wiley & Sons, Ltd. [source] Purification, crystallization and preliminary crystallographic study of haemoglobin from camel (Camelus dromedarius): a high oxygen-affinity lowland speciesACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 8 2009M. Balasubramanian Haemoglobin is a prototypical allosteric protein that is mainly involved in the transportation of oxygen from the lungs to tissues and of carbon dioxide back to the lungs in an intrinsically coordinated manner to maintain the viability of cells. Haemoglobin from Camelus dromedarius provides an interesting case study of adaptation to life in deserts at extremely high temperatures. An ambition to unravel the integrated structural and functional aspects of the casual survival of this animal at high temperatures led us to specifically work on this problem. The present work reports the preliminary crystallographic study of camel haemoglobin. Camel blood was collected and the haemoglobin was purified by anion-exchange chromatography and crystallized using the hanging-drop vapour-diffusion method under buffered high salt concentration using PEG 3350 as a precipitant. Intensity data were collected using a MAR 345 dtb image-plate detector system. Camel haemoglobin crystallized in the monoclinic space group P21, with one whole biological molecule (,2,2) in the asymmetric unit and unit-cell parameters a = 52.759, b = 116.782, c = 52.807,Å, , = 120.07°. [source] Effects of ionic strength on lysozyme uptake rates in cation exchangers.BIOTECHNOLOGY & BIOENGINEERING, Issue 2 2005I: Uptake in SP Sepharose FF Fluorescence scanning confocal microscopy was used in parallel with batch uptake and breakthrough measurements of transport rates to study the effect of ionic strength on the uptake of lysozyme into SP Sepharose FF. In all cases the adsorption isotherms were near-rectangular. As described previously, the intraparticle profiles changed from slow-moving self-sharpening fronts at low salt concentration, to fast-moving diffuse profiles at high salt concentration, and batch uptake rates correspondingly increased with increasing salt concentration. Shrinking core and homogeneous diffusion frameworks were used successfully to obtain effective diffusivities for the low salt and high salt conditions, respectively. The prediction of column breakthrough was generally good using these frameworks, except for low-salt uptake results. In those cases, the compressibility of the stationary phase coupled with the shrinking core behavior appears to reduce the mass transfer rates at particle-particle contacts, leading to shallower breakthrough curves. In contrast, the fast uptake rates at high ionic strength appear to reduce the importance of mass transfer limitations at the particle contacts, but the confocal results do show a flow rate dependence on the uptake profiles, suggesting that external mass transfer becomes more limiting at high ionic strength. These results show that the complexity of behavior observable at the microscopic scale is directly manifested at the column scale and provides a phenomenological basis to interpret and predict column breakthrough. In addition, the results provide heuristics for the optimization of chromatographic conditions. © 2005 Wiley Periodicals, Inc. [source] Expression and purification of F-plasmid RepE and preliminary X-ray crystallographic study of its complex with operator DNAACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 4 2007Chieko Wada The replication initiator factor RepE of the F plasmid in Escherichia coli is an essential protein that stringently regulates the F-plasmid copy number. The RepE protein has a dual function: its monomer functions as a replication initiator, while its dimer acts as a transcriptional repressor of the repE gene. The wild-type dimeric RepE protein was expressed as an N-terminal histidine-tagged protein, purified under native conditions with a high salt concentration and crystallized in complex with the repE operator DNA using the sitting-drop vapour-diffusion technique. The crystals diffracted to a resolution of 3.14,Å after the application of dehydration and crystal annealing and belong to space group P21, with unit-cell parameters a = 60.73, b = 99.32, c = 95.00,Å, , = 108.55°. [source] How applicable is the general adaptation syndrome to the unicellular Tetrahymena?CELL BIOCHEMISTRY AND FUNCTION, Issue 1 2009György Csaba Abstract Hormone receptors, hormones and signal transduction pathways characteristic of higher vertebrates can be observed also in the unicellular Tetrahymena. Previous work showed that stress conditions (starvation, high temperature, high salt concentration, formaldehyde or alcohol treatment) elevated the intracellular level of four hormones (ACTH, endorphin, serotonin and T3). Here, the effect of other stressors (CuSO4 poisoning, tryptophan hydroxylase inhibitor parachlorphenylalanine (PCPA) treatment) on the same and other hormones (epinephrine, insulin, histamine) was studied, using immunocytochemistry and flow cytometric analysis. It was found, that each effect increased the intracellular hormone contents, but some hormones (histamine, T3) were less reactive. Insulin,which is a life-saving factor for Tetrahymena,itself provoked elevation of hormone amounts in association with a stressor, further increased the level of hormones. It was concluded that the ancestor of Selye's General Adaptation Syndrome (GAS) can be found already at unicellular level, and this possibly has a life saving function. Copyright © 2008 John Wiley & Sons, Ltd. [source] Salt-resistant homodimeric bactenecin, a cathelicidin-derived antimicrobial peptideFEBS JOURNAL, Issue 15 2008Ju Y. Lee The cathelicidin antimicrobial peptide bactenecin is a ,-hairpin molecule with a single disulfide bond and broad antimicrobial activity. The proform of bactenecin exists as a dimer, however, and it has been proposed that bactenecin is released as a dimer in vivo, although there has been little study of the dimeric form of bactenecin. To investigate the effect of bactenecin dimerization on its biological activity, we characterized the dimer's effect on phospholipid membranes, the kinetics of its bactericidal activity, and its salt sensitivity. We initially synthesized two bactenecin dimers (antiparallel and parallel) and two monomers (,-hairpin and linear). Under oxidative folding conditions, reduced linear bactenecin preferentially folded into a dimer forming a ladder-like structure via intermolecular disulfide bonding. As compared to the monomer, the dimer had a greater ability to induce lysis of lipid bilayers and was more rapidly bactericidal. Interestingly, the dimer retained antimicrobial activity at physiological salt concentrations (150 mm NaCl), although the monomer was inactivated. This salt resistance was also seen with bactenecin dimer containing one intermolecular disulfide bond, and the bactenecin dimer appears to undergo multimeric oligomerization at high salt concentrations. Overall, dimeric bactenecin shows potent and rapid antimicrobial activity, and resists salt-induced inactivation under physiological conditions through condensation and oligomerization. These characteristics shed light on the features that a peptide would need to serve as an effective therapeutic agent. [source] Use of associating polymers as multifunctional thickeners: studies of Their structure in aqueous solutions via nmr, qels, fluorescence, And rheology measurementsINTERNATIONAL JOURNAL OF COSMETIC SCIENCE, Issue 5 2007Katsunori Yoshida The solution properties of an associating polymer were studied by NMR, quasi-elastic light scattering (QELS), fluorescence, and rheology measurements. An associative thickening (AT) polymer was designed having a nonionic poly(ethylene oxide) backbone with long alkyl chains at both ends to achieve high viscosity even at relatively high salt concentrations and over a wide pH range. This study focuses on the associative state of the polymer in aqueous solutions at various polymer concentrations. In a fluorescence probe study using pyrene a spectral change in the I3/I1 ratio was observed for pyrene at a polymer concentration (Cp) of 3 x 10 -4%, indicating an apparent critical concentration (cmc) of the amphiphilic polymer. The viscosity, self-diffusion coefficient (Dsel), and hydrodynamic size (Rh) distribution measurements at various Cp all suggest that there is a second transition at Cp, 0.4%. Although we observed the discontinuity in viscosity, Dsel, and Rh at Cp, 0.4%, no changes in the relaxation times (T1 and T2) were recognized for either the alkyl chain or the ethylene oxide moiety of the polymer at C p= 0.1,1%. These data suggest that there are no structural changes or phase transitions at Cp, 0.4%, but that intermicellar networks are presumably formed by bridging of the end alkyl groups of the polymer, which is driven by hydrophobic forces. Because the polymer forms networks by hydrophobic interaction and the polymer itself is nonionic, the viscosity of the polymer solution was influenced very little by either the addition of salt or a pH change, as would be expected. The dynamic viscoelastic study revealed that the polymer solution exhibits a single mode Maxwell type relaxation behavior with a terminal relaxation time of about 0.61 s, which imparts a unique flow appearance to the polymer solutions. The time course measurements of the dynamic elastic modulus of the stratum corneum revealed that the polymer has excellent potential for skin softening. It was concluded that the associative thickening polymer not only is a useful thickener with a salt and pH tolerance but also has beneficial skincare effects. [source] The growth limits of a large number of Listeria monocytogenes strains at combinations of stresses show serotype- and niche-specific traitsJOURNAL OF APPLIED MICROBIOLOGY, Issue 5 2008S. Van Der Veen Abstract Aims:, The aim of this study was to associate the growth limits of Listeria monocytogenes during exposure to combined stresses with specific serotypes or origins of isolation, and identify potential genetic markers. Methods and Results:, The growth of 138 strains was assessed at different temperatures using combinations of low pH, sodium lactate, and high salt concentrations in brain heart infusion broth. None of the strains was able to grow at pH , 4·4, aw , 0·92, or pH , 5·0 combined with aw , 0·94. In addition, none of the strains grew at pH , 5·2 and NaLac , 2%. At 30°C, the serotype 4b strains showed the highest tolerance to low pH and high NaCl concentrations at both pH neutral (pH 7·4) and mild acidic conditions (pH 5·5). At 7°C, the serotype 1/2b strains showed the highest tolerance to high NaCl concentrations at both pH 7·4 and 5·5. Serotype 1/2b meat isolates showed the highest tolerance to low pH in the presence of 2% sodium lactate at 7°C. ORF2110 and gadD1T1 were identified as potential biomarkers for phenotypic differences. Conclusions:, Differences in growth limits were identified between specific L. monocytogenes strains and serotypes, which could in some cases be associated with specific genetic markers. Significance and Impact of the Study:, Our data confirm the growth limits of L. monocytogenes as set out by the European Union for ready-to-eat foods and provides an additional criterion. The association of L. monocytogenes serotypes with certain stress responses might explain the abundance of certain serotypes in retail foods while others are common in clinical cases. [source] Effect of Water Phase Salt Content and Storage Temperature on Listeria monocytogenes Survival in Chum Salmon (Oncorhynchus keta) Roe and Caviar (Ikura)JOURNAL OF FOOD SCIENCE, Issue 5 2007Joong-Han Shin ABSTRACT:, Salmon caviar, or ikura, is a ready-to-eat food prepared by curing the salmon roe in a brine solution. Other seasonings or flavorants may be added, depending upon the characteristics of the product desired. Listeria monocytogenes growth is a potential risk, since it can grow at high salt concentrations (>10%) and in some products at temperatures as low as 3 °C. Ikura was prepared from chum salmon (Oncorhynchus keta) roe by adding food-grade NaCl to yield water phase salt contents (WPS) of 0.22% (no added salt), 2.39%± 0.18%, 3.50%± 0.19%, and 4.36%± 0.36%. A cocktail containing L. monocytogenes (ATCC 19114, 7644, 19113) was incorporated into the ikura at 2 inoculum levels (log 2.4 and 4.2 CFU/g), and stored at 3 or 7 °C for up to 30 d. L. monocytogenes was recovered by plating onto modified Oxford media. Aerobic microflora were analyzed on plate count agar. Samples were tested at 0, 5, 10, 20, and 30 d. L. monocytogenes did not grow in chum salmon ikura held at 3 °C during 30 d at any salt level tested; however, the addition of salt at these levels did little to inhibit Listeria growth at 7 °C and counts reached 5 to 6 logs CFU/g. Components in the salmon egg intracellular fluid appear to inhibit the growth of L. monocytogenes. Total aerobic microflora levels were slightly lower in products with higher salt contents. These results indicate that temperature control is critical for ikura and similar products, but that products with lower salt contents can be safe, as long as good refrigeration is maintained. [source] Antibiotics that inhibit cell wall biosynthesis induce expression of the Bacillus subtilis,W and ,M regulonsMOLECULAR MICROBIOLOGY, Issue 5 2002Min Cao Summary Bacillus subtilis encodes seven extracytoplasmic function (ECF) sigma factors. The ,W regulon includes functions involved in detoxification and protection against antimicrobials, whereas ,M is essential for growth at high salt concentrations. We now report that antibiotics that inhibit cell wall biosynthesis induce both ,W and ,M regulons as monitored using DNA microarrays. Induction of selected ,W -dependent genes was confirmed using lacZ reporter fusions and Northern blot analysis. The ability of vancomycin to induce the ,W regulon is dependent on both ,W and the cognate anti- , , RsiW, but is independent of the transition state regulator AbrB. These results suggest that the membrane-localized RsiW anti- ,W factor mediates the transcriptional response to cell wall stress. Our findings are consistent with the idea that one function of ECF , factors is to coordinate antibiosis stress responses and cell envelope homeostasis. [source] Acquisition of double-stranded DNA-binding ability in a hybrid protein between Escherichia coli CspA and the cold shock domain of human YB-1MOLECULAR MICROBIOLOGY, Issue 3 2000Nan Wang Escherichia coli CspA, a major cold shock protein, is dramatically induced upon temperature downshift. As it binds co-operatively to single-stranded DNA (ssDNA) and RNA without apparent sequence specificity, it has been proposed that CspA acts as an RNA chaperone to facilitate transcription and translation at low temperature. CspA consists of a five-stranded ,-barrel structure containing two RNA-binding motifs, RNP1 and RNP2. Eukaryotic Y-box proteins, such as human YB-1, are a family of nucleic acid-binding proteins that share a region of high homology with CspA (43% identity), termed the cold shock domain (CSD). Their cellular functions are very diverse and are associated with growth-related processes. Here, we replaced the six-residue loop region of CspA between the ,3 and ,4 strands with the corresponding region of the CSD of human YB-1 protein. The resulting hybrid protein became capable of binding to double-stranded DNA (dsDNA) in addition to ssDNA and RNA. The dsDNA-binding ability of an RNP1 point mutant (F20L) of the hybrid was almost unchanged. On the other hand, the dsDNA-binding ability of the hybrid protein was abolished in high salt concentrations in contrast to its ssDNA-binding ability. These results indicate that the loop region between the ,3 and ,4 strands of Y-box proteins, which is a little longer and more basic than that of CspA, plays an important role in their binding to dsDNA. [source] Effect of Salt Stress on Carbon Metabolism and Bacteroid Respiration in Root Nodules of Common Bean (Phaseolus vulgaris L.)PLANT BIOLOGY, Issue 4 2000A. Ferri Abstract: In the present work, we examined the effect of salinity on growth, N fixation and carbon metabolism in the nodule cytosol and bacteroids of Phaseolus vulgaris, and measured the O2 consumption by bacteroids incubated with or without the addition of exogenous respiratory substrates. The aim was to ascertain whether the compounds that accumulate under salt stress can increase bacteroid respiration and whether this capacity changes in response to salinity in root nodules of Phaseolus vulgaris. The plants were grown in a controlled environment chamber, and 50, 100 mM or no NaCl (control) was added to the nutrient solution. Two harvests were made, at the vegetative growth period and at the beginning of the reproductive period. The enzyme activities in the nodule cytosol were reduced by the salt treatments, while in the bacteroid cytosol the enzyme activities increased at high salt concentrations at the first harvest and for ADH in all treatments. The data presented here confirm that succinate and malate are the preferred substrates for bacteroid respiration in common bean, but these bacteroids may also utilize glucose, either in control or under saline conditions. The addition of proline or lactate to the incubation medium significantly raised oxygen consumption in the bacteroids isolated from plants treated with salt. [source] Probing protein structure and dynamics by second-derivative ultraviolet absorption analysis of cation,, interactionsPROTEIN SCIENCE, Issue 10 2006Laura H. Lucas Abstract We describe an alternate approach for studying protein structure using the detection of ultraviolet (UV) absorbance peak shifts of aromatic amino acid side chains induced by the presence of salts. The method is based on the hypothesis that salt cations (Li+, Na+, and Cs+) of varying sizes can differentially diffuse through protein matrices and interact with benzyl, phenyl, and indole groups through cation,, interactions. We have investigated the potential of this method to probe protein dynamics by measuring high resolution second-derivative UV spectra as a function of salt concentration for eight proteins of varying physical and chemical properties and the N -acetylated C -ethyl esterified amino acids to represent totally exposed side chains. We show that small shifts in the wavelength maxima for Phe, Tyr, and Trp in the presence of high salt concentrations can be reliably measured and that the magnitude and direction of the peak shifts are influenced by several factors, including protein size, charge, and the local environment and solvent accessibility of the aromatic groups. Evaluating the empirical UV spectral data in light of known protein structural information shows that probing cation,, interactions in proteins reveals unique information about the influence of structure on aromatic side chain spectroscopic behavior. [source] Structure and epimerase activity of anthocyanidin reductase from Vitis viniferaACTA CRYSTALLOGRAPHICA SECTION D, Issue 9 2009Mahmoud Gargouri Together with leucoanthocyanidin reductase, anthocyanidin reductase (ANR) is one of the two enzymes of the flavonoid-biosynthesis pathway that produces the flavan-3-ol monomers required for the formation of proanthocyanidins or condensed tannins. It has been shown to catalyse the double reduction of anthocyanidins to form 2R,3R -flavan-3-ols, which can be further transformed to the 2S,3R isomers by non-enzymatic epimerization. ANR from grape (Vitis vinifera) was expressed in Escherichia coli and purified. Unexpectedly, RP-HPLC, LC-MS and NMR experiments clearly established that the enzyme produces a 50:50 mixture of 2,3- cis and 2,3- trans flavan-3-ols which have been identified by chiral chromatography to be 2S,3S - and 2S,3R -flavan-3-ols, i.e. the naturally rare (+)-epicatechin and (,)-catechin, when cyanidin is used as the substrate of the reaction. The first three-dimensional structure of ANR is described at a resolution of 2.2,Å and explains the inactivity of the enzyme in the presence of high salt concentrations. [source] | |||||||||||||