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1.
Secondary chemical shift analysis is the main NMR method for detection of transiently formed secondary structure in intrinsically
disordered proteins. The quality of the secondary chemical shifts is dependent on an appropriate choice of random coil chemical
shifts. We report random coil chemical shifts and sequence correction factors determined for a GGXGG peptide series following
the approach of Schwarzinger et al. (J Am Chem Soc 123(13):2970–2978, 2001). The chemical shifts are determined at neutral pH in order to match the conditions of most studies of intrinsically disordered
proteins. Temperature has a non-negligible effect on the 13C random coil chemical shifts, so temperature coefficients are reported for the random coil chemical shifts to allow extrapolation
to other temperatures. The pH dependence of the histidine random coil chemical shifts is investigated in a titration series,
which allows the accurate random coil chemical shifts to be obtained at any pH. By correcting the random coil chemical shifts
for the effects of temperature and pH, systematic biases of the secondary chemical shifts are minimized, which will improve
the reliability of detection of transient secondary structure in disordered proteins. 相似文献
2.
Jen-Ping Chung Tsu-Liang Chang Albert Yu-Ming Chi Chou Tou Shii 《Plant Cell, Tissue and Organ Culture》2006,87(3):305-314
Embryogenic cell suspensions of Musa AAA and AAB genomic groups were cultured in a maintenance culture medium for 17 generations (lasting for 238 days). The cell growth phases and medium pH changes were also observed correspondingly. Three major growth phases of AAA genomic group have been focused, namely cell releasing, proliferation and globularization phases. During almost all the subculture generations the cell stocks of AAB ‘Raja’ were continuously characterized by proliferating cell aggregates while the globularization phase occurred only for short duration. The medium acidity levels of the cell stocks of AAA ‘Pei-Chiao’ and ‘Robusta’ were commonly scattered in a wider range of pH 3.3–5.3, while the AAB ‘Raja’ were deviated in a narrow range of pH 4.0–4.6. After subculture, culture medium showed biphasic pH changes, which were drastic pH falls followed by an auto-regulated steady-state level. The steady-state pH values in each of the three growth phases (i.e. cell releasing, proliferation and globularization phases) were of 3.3–4.0, 4.0–4.8 and 4.8–5.3 respectively. Morphological bipolarity and the efficiency in the formation of somatic embryos have been thoroughly discussed. Reported research indicates that the condition of pH below 4.6 may prevent the development of embryogenic cells towards polar growth. 相似文献
3.
Biomass granulation in an aerobic:anaerobic-enhanced biological phosphorus removal process in a sequencing batch reactor with varying pH 总被引:1,自引:0,他引:1
Johwan Ahn Simon McIlroy Sarah Schroeder Robert Seviour 《Journal of industrial microbiology & biotechnology》2009,36(7):885-893
Long-term influences of different steady-state pH conditions on microbial community composition were determined by fluorescence
in situ hybridization (FISH) in a laboratory scale reactor configured for enhanced biological phosphorus removal (EBPR). Chemical
profiles were consistent with shifts in populations from polyphosphate-accumulating organisms (PAO) to glycogen-accumulating
organisms (GAO) when pH fell from pH 7.5 to 7.0 and then to 6.5. While biomass was both dispersed and flocculated at pH 7.5,
almost complete granulation occurred gradually after pH was dropped to 7.0, and these granules increased in size as the pH
was reduced further to 6.5. Reverting back to pH 7.5 led to granule breakdown and corresponding increases in anaerobic phosphate
release. Granules consisted almost entirely of Accumulibacter PAO cells, while putative GAO populations were always present in small numbers. Results suggest that low pH may contribute
to granulation under these operational conditions. While chemical profiles suggested the PAO:GAO balance was changing as pH
fell, FISH failed to reveal any marked corresponding increase in GAO abundances. Instead, TEM evidence suggested the Accumulibacter PAO phenotype was becoming more like that of a GAO. These data show how metabolically adaptable the Accumulibacter PAO can be under anaerobic:aerobic conditions in being able to cope with marked changes in plant conditions. They suggest
that decreases in EBPR capacity may not necessarily reflect shifts in community composition, but in the existing population
metabolism. 相似文献
4.
The critical micellar concentration (CMC) of stearoylcarnitine was determined at different pH values at room temperature by fluorescence spectroscopy, monitoring the spectral changes of 8-anilinonaphthalene-1-sulfonate (ANS). The CMC was found to vary with pH, increasing from about 10 μM at pH 3.0 to ca. 25 μM at pH 7.0, but decreasing slightly with further increase in pH to approximately 19 μM at pH 10.0. Differential scanning calorimetry (DSC) shows that stearoylcarnitine dispersed in water at low concentration undergoes a broad thermotropic phase transition at 44.5°C, with a transition enthalpy of 15.0 kcal/mol. The transition temperature (T
t) shifts to ca. 50.5°C in the presence of 1 mM EDTA or when the concentration is increased significantly. The turbidity of aqueous dispersions of stearoylcarnitine was found to be considerably high at low temperatures, which decreases quite abruptly over a short temperature range, indicating that a transition occurs from a phase of large aggregates to one of much smaller aggregates, most likely micelles. The phase transition temperature was determined as 29.1°C at pH 3.0, which increased with increasing pH up to a value of 55.3°C at pH 8.6 and remains nearly constant thereafter up to pH 11.2. The pH dependence of CMC and T
t suggest that the pK
a of the carboxyl group of long chain acylcarnitines shifts to higher temperatures upon aggregation (micelles or bilayer membranes). 相似文献
5.
Soret spectral contributions of the α-subunit heme pocket have been evaluated by performing static titrations of apohemoglobin
A with CNProtohemin under varied experimental conditions. Increasing the temperature from 5 to 30°C in 0.05 M potassium phosphate buffer, pH 7, resulted in a decreasingly prominent hypsochromic shifts reflecting altered the vinyl–globin
interactions. Studies at 10°C in over pH range of 6.7–8.0 revealed a profile for the spectral shifts approximating the side
chain pK value (7.4) a histidyl residue. These overall spectral changes correspond to ΔE of ≤7 kJ/mol indicative of electrostatic noncovalent interactions. Further our current molecular modeling studies indicate
that the spatial arrangement and critical noncovalent interactions of tyrosine 42 and histidine 45 (aromatic residues unique to the α-subunit) make significant contribution to the Soret spectra. Most interestingly, phylogenetic
analyses have revealed the presence of a histidyl triad in the α-chain of all vertebrates that form heterotetramers. 相似文献
6.
David J. Wilton Ryo Kitahara Kazuyuki Akasaka Mike P. Williamson 《Journal of biomolecular NMR》2009,44(1):25-33
Pressure-dependent 13C chemical shifts have been measured for aliphatic carbons in barnase and Protein G. Up to 200 MPa (2 kbar), most shift changes
are linear, demonstrating pressure-independent compressibilities. CH3, CH2 and CH carbon shifts change on average by +0.23, −0.09 and −0.18 ppm, respectively, due to a combination of bond shortening
and changes in bond angles, the latter matching one explanation for the γ-gauche effect. In addition, there is a residue-specific component, arising from both local compression and conformational
change. To assess the relative magnitudes of these effects, residue-specific shift changes for protein G were converted into
structural restraints and used to calculate the change in structure with pressure, using a genetic algorithm to convert shift
changes into dihedral angle restraints. The results demonstrate that residual 13Cα shifts are dominated by dihedral angle changes and can be used to calculate structural change, whereas 13Cβ shifts retain significant dependence on local compression, making them less useful as structural restraints. 相似文献
7.
A. V. Alova A. A. Bulychev A. A. Cherkashin 《Biochemistry (Moscow) Supplemental Series A: Membrane and Cell Biology》2012,6(3):227-234
Activities of ion pumps and H+-conducting channels in the plasmalemma of illuminated characean algae are distributed inhomogeneously along the internode,
which accounts for the shifts of surface pH up to 3.5 units between various cells regions. Spatial variations in cytoplasmic
properties provide the basis for uneven distribution of photosynthetic activity along the cell length and might affect the
operation of H+-transporting systems at the tonoplast. In order to visualize the longitudinal distribution of the vacuolar pH in Chara corallina internodal cells, the pH microelectrode was inserted into the vacuole and the cell sap was gradually displaced along the
cell during intracellular perfusion with an artificial medium. Fluorescein was added to the perfusion medium as a fluorescent
marker to detect the arrival of the replacing medium into the area of pH and fluorescence measurements. In light-adapted cells,
nonuniform longitudinal pH profiles were observed, with pH shifts as large as 2–2.5 units. In dark-adapted cells, the pH shifts
in longitudinal profiles did not exceed 0.5 pH units. The occurrence of large pH changes within the vacuole of individual
internodes indicates the possibility of nonuniform distribution of the tonoplast H+-transporting systems in different regions of the illuminated cell. 相似文献
8.
Dietary fibres from Ulva lactuca (L.) Thuret (sea lettuce) and Enteromorpha compressa (L.) Grev. (A.O. nori) were measured according to a ‘standard’ method and a ‘physiological’ protocol simulating the gastric
and intestinal environments. U. lactuca contained 15.8–8.0% soluble and 24.2–32.6% insoluble fibres according to the ‘standard’ and ‘physiological’ methods, respectively.
For E. compressa, these values were 14.9–15.9 and 21.6–28.7%, respectively. For both algae, the composition suggests that the soluble fibres
were xylorhamnoglycuronans sulphates and insoluble fibres were essentially composed of glucans. No marked chemical compositional
variation was observed between soluble fractions extracted under the simulated gastric and intestinal conditions. Fibres in
both algae are hydrophilic but the water holding capacities were higher after extraction of soluble fibres (5.5–9.5 g g−1 for the dry algae; 14.0–16.0 g g−1 for the standard insoluble fibres). Water soluble fibres demonstrated low intrinsic viscosities at 37 °C in buffers, particularly
those from E. compressa (36.0–36.5 ml g−1), and was affected by pH for those of U. lactuca (147.5 ml g−1 at pH 3.0 and 175.0 ml g−1 at pH 7.3). 相似文献
9.
Autolytic degradation of yeast RNA occurs in many foods and beverages and can impact on the sensory quality of the product,
but the resulting complex mixture of nucleotides, nucleosides and nucleobases has not been properly characterised. In this
study, yeast autolysis was induced by incubating cell suspensions of Saccharomyces cerevisiae at 30–60 °C (pH 7.0), and at pH 4.0–7.0 (40 °C) for 10–14 days, and the RNA degradation products formed during the process
were determined by reversed-phase HPLC. Up to 95% of cell RNA was degraded, with consequent leakage into the extracellular
environment of mainly 3′-, 5′- and 2′-ribonucleotides, and lesser amounts of polynucleotides, ribonucleosides and nucleobases.
The rate of RNA degradation and the composition of the breakdown products varied with temperature and pH. RNA degradation
was fastest at 50 °C (pH 7.0). Autolysis at lower temperatures (30 °C and 40 °C) and at pH 5.0 and 6.0 favoured the formation
of 3′-nucleotides, whereas autolysis at 40 °C and 50 °C (pH 7.0) favoured 5′- and 2′-nucleotides. The best conditions for
the formation of the two flavour-enhancing nucleotides, 5′-AMP and 5′-GMP, were 50 °C (pH 7.0) and pH 4.0 (40 °C), respectively. 相似文献
10.
Biochemical characterisation of the esterase activities of wine lactic acid bacteria 总被引:1,自引:0,他引:1
Esters are an important group of volatile compounds that can contribute to wine flavour. Wine lactic acid bacteria (LAB) have
been shown to produce esterases capable of hydrolysing ester substrates. This study aims to characterise the esterase activities
of nine LAB strains under important wine conditions, namely, acidic conditions, low temperature (to 10°C) and in the presence
of ethanol (2–18% v/v). Esterase substrate specificity was also examined using seven different ester substrates. The bacteria
were generally found to have a broad pH activity range, with the majority of strains showing maximum activity close to pH 6.0.
Exceptions included an Oenococcus oeni strain that retained most activity even down to a pH of 4.0. Most strains exhibited highest activity across the range 30–40°C.
Increasing ethanol concentration stimulated activity in some of the strains. In particular, O. oeni showed an increase in activity up to a maximum ethanol concentration of around 16%. Generally, strains were found to have
greater activity towards short-chained esters (C2–C8) compared to long-chained esters (C10–C18). Even though the optimal physicochemical
conditions for enzyme activity differed from those found in wine, these findings are of potential importance to oenology because
significant activities remained under wine-like conditions. 相似文献
11.
G. I. Karavaiko T. F. Kondrat’eva E. E. Savari N. V. Grigor’eva Z. A. Avakyan 《Microbiology》2000,69(2):167-173
The role played by a bacterial community composed ofPseudomonas putida, strain 21;Pseudomonas stutzeri, strain 18; andPseudomonas sp., strain 5, and by physical and chemical factors in the degradation of CN− and SCN− was studied. It was shown that the degradation of CN− is determined both by the action of bacteria and by abiotic physical and chemical factors (pH, O2, temperature, the medium agitation rate, etc.). The contribution of chemical degradation was found to increase drastically
at pH below 9.0; when air was blown through the medium (irrespective of the pH value); under active agitation of the medium;
and when the medium surface interfacing air was increased. Even at elevated pH values (9.0-9.2), suboptimal for bacterial
growth, the microbial degradation could account for at most 20–25 mg/1 of CN−, regardless of its initial concentration. When CN− and SCN− were concurrently present in the medium, the former compound was the first to be degraded by microorganisms. The rate of
bacterial degradation of SCN− under continuous cultivation in a chain of reactors was found to depend on its concentration, the medium flow rate, agitation
rate, and the pattern of carbon source supply and could exceed 1 g/(l day). CN− and SCN− are utilized by bacteria solely as nitrogen sources. The mechanism of CN− and SCN− degradation by the microbial community is discussed.
Deceased. 相似文献
12.
We describe short-term changes in foraging behavior by wild Yakushima macaques (Macaca fuscata yakui),which inhabit a warm-temperate broad—leaved forest on Yakushima Island (30°N, 131°E), Japan. Rapid changes of dietary composition,
activity budget, and range use by the monkeys occurred from May to June, apparently associated with changes in the availability
of the fruit of Myrica rubraBefore the fruit ripened, monkeys spent less time moving and more time feeding on many species of leaves, which accounted
for 40% of feeding time. However, when M. rubrabegan to ripen, they fed intensively on the fruit, which accounted for three-fourths of feeding time,though the activity budget remained unaffected As fiuit of M. rubradecreased,the monkeys fed more on the fruit of other species and on insects, and spent more time moving at higher speeds. There marked
shifts in foraging pattern occurred within only two months. In terms of moving cost and dietary quality,Yakushima macaques shifted their foraging pattern according to the availability of M. rubrafrom a “low-cost, low-yield” strategy to a “low-cost, high-yield” strategy, and then to a more costly strategy. The ability
to make such rapid shifts in foraging pattern may allow the macaques to effectively use the highly variable food supply within
their small range. 相似文献
13.
Mika Murata Masaru Nagai Makoto Takao Akira Suzuki Takuo Sakai Takao Terashita 《Mycoscience》2001,42(5):479-482
Trehalase from the culture filtrate ofLentinula edodes was purified and characterized. Molecular masses were estimated to be 158 kDa and 79–91 kDa by gel filtration and SDS-PAGE
under the reduced condition, respectively. The enzyme was composed of two identical subunits and contained carbohydrate molecules.
The optimum temperature and pH were obtained at around 40°C and pH 5.0, respectively. The enzyme was stable up to 40°C and
in a range pH of 4–10 at 30°C. It cleaved α-1,1 linkages of trehalose, but not α-1,4, α-1,6 or β-1,4 glycosyl linkages, and
was defined as an acid trehalase. 相似文献
14.
An inhibitor of trypsin and chymotrypsin was purified from horse gram (Dolichos biflorus) beans. The concentration of the inhibitor which provided total inhibition was 0.27 Μg/Μg tryptic enzyme and 0.46 Μg/Μg chymotryptic
enzyme. The inhibitor was stable at 37‡C between pH of 3 to 11 and at 97‡C, upto pH 5.0 only. While the activities were rapidly
lost in 0.1N NaO H the loss was only 5 0% in 0.1N HCl when kept for 2 h at 97‡C. On heating at pH 7.8, it remained stable
upto 80‡C with a gradual loss in activities at 97‡C and a total loss occurring by autoclaving at 15 psi for 10 min. Reduction
of disulphide bonds by 2-mercapto-ethanol, pronase digestion and boiling in the presence of 1 M NaCl led to reduction in the
activities. However, the inhibitor was resistant to the action of pepsin and subtilisin and to urea at 37‡C. 相似文献
15.
Citric acid production from sucrose using a recombinant strain of the yeast Yarrowia lipolytica 总被引:1,自引:0,他引:1
Förster A Aurich A Mauersberger S Barth G 《Applied microbiology and biotechnology》2007,75(6):1409-1417
The yeast Yarrowia lipolytica is able to secrete high amounts of several organic acids under conditions of growth limitation and carbon source excess.
Here we report the production of citric acid (CA) in a fed-batch cultivation process on sucrose using the recombinant Y. lipolytica strain H222-S4(p67ICL1) T5, harbouring the invertase encoding ScSUC2 gene of Saccharomyces cerevisiae under the inducible XPR2 promoter control and multiple ICL1 copies (10–15). The pH-dependent expression of invertase was low at pH 5.0 and was identified as limiting factor of the CA-production
bioprocess. The invertase expression was sufficiently enhanced at pH 6.0–6.8 and resulted in production of 127–140 g l−1 CA with a yield Y
CA of 0.75–0.82 g g−1, whereas at pH 5.0, 87 g l −1 with a yield Y
CA of 0.51 gg−1 were produced. The CA-productivity Q
CA increased from 0.40 g l −1 h−1 at pH 5.0 up to 0.73 g l −1 h−1 at pH 6.8. Accumulation of glucose and fructose at high invertase expression level at pH 6.8 indicated a limitation of CA
production by sugar uptake. The strain H222-S4(p67ICL1) T5 also exhibited a gene–dose-dependent high isocitrate lyase expression
resulting in strong reduction (<5%) of isocitric acid, a by-product during CA production. 相似文献
16.
A. Bevilacqua M. R. Corbo M. Mastromatteo M. Sinigaglia 《World journal of microbiology & biotechnology》2008,24(9):1721-1729
A four variables-five levels Central Composite Design (CCD) was developed to model the individual and interactive effects
of carbohydrates (lactose or maltose), yeast extract, di-ammonium hydrogen citrate and pH on the biomass production (Abs600 nm), viable and cultivable cell number and acidifying ability of a probiotic strain of Lactobacillus plantarum, isolated from table olives “Bella di Cerignola”. pH values were modeled through a negative Gompertz equation, in order to
obtain the parameter α (metabolic adaptation time). This value and the biomass were submitted to a stepwise procedure and
second order polynomial equations were derived. The parameter α was affected by the initial pH and lactose; the effect of
the maltose, however, was not significant. The biomass production increased with increasing of yeast extract, di-ammonium
hydrogen citrate and maltose concentrations and was maximum at pH 6.0 and 20 g l−1 of lactose. 相似文献
17.
Flagella-based motility of extremely alkaliphilic Bacillus species is completely dependent upon Na+. Little motility is observed at pH values < ∼8.0. Here we examine the number of flagella/cell as a function of growth pH
in the facultative alkaliphile Bacillus pseudofirmus OF4 and a derivative selected for increased motility on soft agar plates. Flagella were produced by both strains during growth
in a pH range from 7.5 to 10.3. The number of flagella/cell and flagellin levels of cells were not strongly dependent on growth
pH over this range in either strain although both of these parameters were higher in the up-motile strain. Assays of the swimming
speed indicated no motility at pH < 8 with 10 mM Na+, but significant motility at pH 7 at much higher Na+ concentrations. At pH 8–10, the swimming speed increased with the increase of Na+ concentration up to 230 mM, with fastest swimming at pH 10. Motility of the up-motile strain was greatly increased relative
to wild-type on soft agar at alkaline pH but not in liquid except when polyvinylpyrrolidone was added to increase viscosity.
The up-motile phenotype, with increased flagella/cell may support bundle formation that particularly enhances motility under
a subset of conditions with specific challenges. 相似文献
18.
Uchida H Hojyo M Fujii Y Maeda Y Kajimura R Yamanaka H Sakurai A Sakakibara M Aisaka K 《Applied microbiology and biotechnology》2007,74(4):805-812
Formate oxidase was found in cell-free extracts of Debaryomyces vanrijiae MH201, a soil isolate. After purification by column chromatography, the preparation showed a protein band corresponding to
a molecular mass (MM) of 64 kDa on sodium dodecyl sulfate–polyacrylamide gel electrophoresis. The MM, estimated by a gel filtration,
was 99 kDa. The preparation showed two and three bands on isoelectric focusing under denaturing and native conditions, respectively.
These results suggest that the preparation contained three isoforms, each of which might be composed of αα, αβ, and ββ subunits
with apparently similar MM. The preparation acted on formate with K
m and V
max values of 11.7 mM and 262 μmol min−1 mg−1, respectively, at pH 4.5 and 25°C, but showed no evidence of activity on the other compounds tested. The optimum pH and temperature
were pH 4.0 and 35°C, respectively. The preparation showed activities of 85% of the initial activity after storage at pH 6.0
and 4°C for 8 weeks. When 10 mM formaldehyde was reacted with 2.0 U ml−1 of the enzyme preparation at pH 5.5 and room temperature in the presence of 2.0 U ml−1 of a microbial aldehyde oxidase and 100 U ml−1 of catalase for 180 min, neither of formate nor formaldehyde was detected, suggesting that the reaction involved the quantitative
conversion of formaldehyde to carbon dioxide. 相似文献
19.
Bing-xue Li Ning Zhang Qing Peng Tie Yin Fei-fei Guan Gui-li Wang Ying Li 《Applied microbiology and biotechnology》2009,84(2):293-300
A black yeast strain “NG” was isolated from strawberry fruit and identified as Aureobasidium pullulans. Strain NG displayed yeast-like cell (YL), swollen cell (SC), septate swollen cell (SSC), meristematic structure (MS), and
chlamydospore (CH) morphologies. pH was the key factor regulating cell morphogenesis of strain NG. Differentiation of YL controlled
by extracellular pH had no relationship with nutrition level. YL was maintained at pH >6.0, but was transformed into SC at
pH ∼4.5. SC, a stable cell type of A. pullulans, could bud, septate, or transform into MS or CH, in response to nutrition level and low pH. SC produced swollen cell blastospores
(SCB) at pH 2.1 with abundant nutrition, and could transform into MS at lower pH (1.5). SC was induced to form CH by low level
nutrition and pH <3, and this transition was suppressed by adjusting pH to ∼4.5. Crude polysaccharides without pigment (melanin)
were produced by SC of strain NG. Pullulan content of the polysaccharides was very high (98.37%). Fourier-transform infrared
spectroscopy confirmed that chemical structures of the polysaccharides and standard pullulan were identical. Swollen cells
produced 2.08 mg/ml non-pigmented polysaccharides at 96 h in YPD medium. Controlling pH of fermentation is an effective and
convenient method to harvest SC for melanin-free pullulan production. 相似文献
20.
Glucoamylase II (EC 3.2.1.3) fromAspergillus niger has 31 % α-helix, 36 %Β- structure and rest aperiodic structure at pH 4.8 as analysed by the method of Provencher and Glockner (1981,Biochemistry, 20,33). In the near ultra-violet circular dichroism spectrum the enzyme exhibits peaks at 304, 289, 282 and 257 nm and troughs
at 285, 277 and 265 nm respectively. The enzyme activity and structure showed greater stability at pH 4.8 than at pH 7.0,
were highly sensitive to alkaline pH but less sensitive to acid pH values. The enzyme retained most of its catalytic activity
and structure even on partial removal of carbohydrate moieties by periodate treatment but was less stable at higher temperatures
and storage at 30‡C. Reduction of the periodate treated enzyme did not reverse the loss of stability. Binding of the synthetic
substrate,p-nitrophenyl-α-D-glucoside, perturbed the environment around aromatic amino acids and caused a decrease in the
ordered structure. 相似文献