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1.
Harald Kosegarten Franz Grolig Andreas Esch Karl-Heinz Glüsenkamp Konrad Mengel 《Planta》1999,209(4):444-452
A fluorimetric ratio technique was elaborated to measure apoplastic pH in the outer root cortex of maize (Zea mays L.) grown hydroponically. A newly synthesized fluorescent probe, fluorescein boronic acid (pKa = 5.48), which covalently binds to the cell wall of the outer cell layers, was used. Under conditions of saturating ion concentrations
the apoplastic pH was determined along the root axis ranging from 1 to 30 mm behind the root tip. Apoplastic pH was recorded
for root segment areas (1 mm2), and pH values of high statistical significance were obtained. With an external solution of pH 5, the apoplastic pH was
about pH 5.1 in the division zone, between pH 4.8 and 4.9 in the elongation region and about pH 4.9 in the root hair zone.
At an external pH of 8.6, the difference between the external pH and the apoplastic pH was considerably more, with a pH of
5.2–5.3 in all root zones. Addition of 1 mM NH4
+ caused a small apoplastic pH decrease (0.05 of a pH unit) in all root zones. Apoplastic alkalization upon application of
6 mM NO3
− was highest (0.3 of a pH unit) in the zone where root hairs emerge; in the division and early elongation zones, apoplastic
pH increased only transiently. In the presence of 10 mM HCO3
−, NO3
− elicited a higher and persistent alkalization (0.06–0.25 of a pH unit) in all root zones. Application of fusicoccin reduced
apoplastic pH from 4.85 to 4.75 in the elongation zone, while inhibition of the H+-ATPase with vanadate alkalized the apoplast in the root hair zone from pH 5.4 to 5.6. The observed pH differences along the
root axis upon differential N supply and application of HCO3
− provide evidence that this new pH technique is a useful tool with which to measure apoplastic pH, and in future may permit
measurements at microsites at the cell level by use of microscope imaging.
Received: 26 August 1998 / Accepted: 4 May 1999 相似文献
2.
A. De Smul J. Dries L. Goethals H. Grootaerd W. Verstraete 《Applied microbiology and biotechnology》1997,48(3):297-303
In a mesophilic (30–35 °C), sulphidogenic, ethanol-fed expanded-granular-sludge-blanket reactor, sulphate, at loading rates
of up to 10.0–12.0 g Sl−1␣day−1, was removed with an average efficiency of more than 80%. The pH was between 7.7 and 8.3 and the maximal total dissolved
sulphide concentration was up to 20 mM S (650 mg S/l). The alkaline pH was maintained by either a pH-control unit with sodium
hydroxide or by stripping part of the sulphide and CO2 from the recycle with nitrogen gas. The superficial upstream liquid velocity (v
up) was 3.0–4.5 m/h. The ratio of ethanol to sulphur was near stoichiometry. At alkaline pH, the activity of the acetotrophic
sulphate-reducing bacteria, growing on acetate, was strongly enhanced, whereas at pH below 7.7 the acetotrophic sulphate-reducing
bacteria were inhibited by aqueous H2S. With regard to the removal efficiency and operational stability, external stripping with N2 and pH control were equally successful.
Received: 2 December 1996 / Received revision: 13 March 1997 / Accepted: 15 March 1997 相似文献
3.
The purpose of this study was to investigate the effect of cyclodextrins (CDs) on aqueous solubility, stability, and in vitro corneal permeability of delta-8-tetrahydrocannabinol (Δ8-THC). Phase solubility of Δ8-THC was studied in the presence of 2-hydroxypropyl-β-cyclodextrin (HPβCD), randomly methylated-β-cyclodextrin (RMβCD) and
sulfobutyl ether-β-cyclodextrin sodium salt (SβCD). Stability of Δ8-THC in 5% w/v aqueous CD solutions, as a function of pH, was studied following standard protocols. In vitro corneal permeation of Δ8-THC (with and without CDs) across excised rabbit cornea was also determined. Phase-solubility profile of Δ8-THC in the presence of both HPβCD and RMβCD was of the AP type, whereas, with SβCD an AL type was apparent. Aqueous solubility of Δ8-THC increased to 1.65, 2.4, and 0.64 mg/mL in the presence of 25% w/v HPβCD, RMβCD, and SβCD, respectively. Significant degradation of Δ8-THC was not observed within the study period at the pH values studied, except for at pH 1.2. Transcorneal permeation of Δ8-THC was dramatically improved in the presence of CDs. The results demonstrate that CDs significantly increase aqueous solubility,
stability, and transcorneal permeation of Δ8-THC. Thus, topical ophthalmic formulations containing Δ8-THC and modified beta CDs may show markedly improved ocular bioavailability. 相似文献
4.
Preformulation studies were performed on a hemiglutarate ester prodrug of Δ9-tetrahydrocannabinol (THC-HG), to facilitate the development of stable formulations by hot-melt methods. The various studies
performed included solid-state thermal characterization, pKa, logP, aqueous and pH dependent solubility, pH stability and
effect of moisture, temperature and oxygen on solid-state stability. A hot-melt method was utilized to fabricate THC-HG incorporated
poly (ethylene oxide) (PEO) matrices and the bioadhesive properties, release profiles and post-processing stability of these
matrices were assessed as a function of the polymer molecular weight. The prodrug exhibited a T
g close to 0°C, indicating its amorphous nature. Thermogravimetric analysis revealed a rapid weight loss after 170°C. The prodrug
exhibited a seven-fold higher aqueous solubility as compared to the parent drug (THC). Also, the solubility of the compound
increased with increasing pH, being maximum at pH 8. The prodrug exhibited a v-shaped pH-rate profile, with the degradation
rate minimum between pH 3 and 4. The moisture uptake and drug degradation increased with an increase in relative humidity.
Solid-state stability indicated that the prodrug was stable at −18°C but demonstrated higher degradation at 4°C, 25°C and
40°C (51.6%, 74.5% and 90.1%, respectively) at the end of 3-months. THC-HG was found to be sensitive to the presence of oxygen.
The release of the active from the polymeric matrices decreased, while bioadhesion increased, with an increase in molecular
weight of PEO. 相似文献
5.
Liu J Zhang Z Liu Z Zhu H Dang H Lu J Cui Z 《Marine biotechnology (New York, N.Y.)》2011,13(5):837-844
The aim of this work was to optimize the fermentation parameters in the shake-flask culture of marine bacterium Wangia sp. C52 to increase cold-adapted amylase production using two statistical experimental methods including Plackett–Burman
design, which was applied to find the key ingredients for the best medium composition, and response surface methodology, which
was used to determine the optimal concentrations of these components. The results showed starch, tryptone, and initial pH
had significant effects on the cold-adapted amylase production. A central composite design was then employed to further optimize
these three factors. The experimental results indicated that the optimized composition of medium was 6.38 g L−1 starch, 33.84 g L−1 tryptone, 3.00 g L−1 yeast extract, 30 g L−1 NaCl, 0.60 g L−1 MgSO4 and 0.56 g L−1 CaCl2. The optimized cultivation conditions for amylase production were pH 7.18, a temperature of 20°C, and a shaking speed of
180 rpm. Under the proposed optimized conditions, the amylase experimental yield (676.63 U mL−1) closely matched the yield (685.60 U mL−1) predicted by the statistical model. The optimization of the medium contributed to tenfold higher amylase production than
that of the control in shake-flask experiments. 相似文献
6.
Hai-Nan Su Bin-Bin Xie Xiu-Lan Chen Jin-Xia Wang Xi-Ying Zhang Bai-Cheng Zhou Yu-Zhong Zhang 《Journal of applied phycology》2010,22(1):65-70
Allophycocyanin (APC) is a minor component of phycobiliproteins in cyanobacteria and red algae. This paper describes a simple
and inexpensive extracting method for isolating APC from Spirulina (Arthrospira) platensis with high efficiency. The crude phycobiliprotein extract was pretreated by ammonium sulfate fractionation. Then, by adding
hydroxylapatite into crude phycobiliprotein extract dissolved in 20 mM phosphate buffer (pH 7.0), APC was selectively adsorbed
by hydroxylapatite but C-phycocyanin (C-PC) was not. The hydroxylapatite was collected and APC was extracted from the crude
phycobiliprotein extract. Then, the enriched APC was washed off from the hydroxylapatite using 100 mM phosphate buffer (pH 7.0).
In this simple extracting method it was easy to remove C-PC and isolate APC in large amounts. The absorbance ratio A
650/A
280 of extracted APC reached 2.0. The recovery yield was 70%, representing 4.61 mg · g−1 wet weight. The extracted APC could be further purified by a simple anion-exchange chromatography with a pH gradient from
5.6 to 4.0. The absorbance ratio A
650/A
280 of the purified APC reached 5.0, and the overall recovery yield was 43%, representing 2.83 mg · g−1 wet weight. Its purity was confirmed by native polyacrylamide gel electrophoresis (PAGE) and sodium dodecyl sulfate-PAGE. 相似文献
7.
M. J. Artolozaga E. Kubátová J. Volc H. M. Kalisz 《Applied microbiology and biotechnology》1997,47(5):508-514
Pyranose 2-oxidase (P2O) was purified 43-fold to apparent homogeneity from the basidiomycete Phanerochaete chrysosporium using liquid chromatography on phenyl Sepharose, Mono Q (twice) and phenyl Superose. The native enzyme has a molecular mass
of about 250 kDa (based on native PAGE) and is composed of four identical subunits of 65 kDa. It contains three isoforms of
isoelectric point (pI) 5.0, 5.05 and 5.15 and does not appear to be a glycoprotein. P2O is optimally stable at pH 8.0 and
up to 60 °C. It is active over a broad pH range (5.0–9.0) with maximum activity at pH 8.0–8.5 and at 55 °C, and a broad substrate
specificity. d-Glucose is the preferred substrate, but 1-β-aurothioglucose, 6-deoxy-d-glucose, l-sorbose, d-xylose, 5-thioglucose, d-glucono-1,5-lactone, maltose and 2-deoxy-d-glucose are also oxidised at relatively high rates. A Ping Pong Bi Bi mechanism was demonstrated for the P2O reaction at
pH 8.0, with a catalytic constant (k
cat) of 111.0 s−1 and an affinity constant (K
m) of 1.43 mM for d-glucose and 83.2 μM for oxygen. Whereas the steady-state kinetics for glucose oxidation were unaffected by the medium at
pH ≥ 7.0, at low pH both pH and buffer composition affected the P2O kinetics with the k
cat/K
m value decreasing with decreasing pH. The greatest effect was observed in acetate buffer (0.1 M, pH 4.5), where the k
cat decreased to 60.9 s−1 and the K
m increased to 240 mM. The activity of P2O was completely inhibited by 10 mM HgCl2, AgNO3 and ZnCl2, and 50% by lead acetate, CuCl2 and MnCl2.
Received: 28 August 1996 / Received revision: 25 November 1996 / Accepted: 29 November 1996 相似文献
8.
C. E. Crocker J. J. Cech Jr. 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1998,168(1):50-60
The effect of environmental hypercapnia on respiratory and acid-base variables was studied in white sturgeon, Acipenser transmontanus. Blood PCO2, PO2, pH, hemoglobin concentration, and plasma lactate, glucose, catecholamines and cortisol were measured first under normocapnia
(water PCO2 < 0.5 Torr, 1 Torr = 133.32 Pa), then under hypercapnia (25–35 Torr) and a final return to normocapnia at 19 ± 0.5 °C. Acute
(≤ 2h) hypercapnia significantly increased arterial PCO2 (8-fold increase), ventilation frequency (2-fold increase), plasma HCO3
− (2.3-fold) and decreased arterial pH (to 7.15 ± 0.02). After 24 h, norepinephrine, epinephrine and cortisol, were significantly
increased, and arterial pH reached its nadir (7.10 ± 0.03). During the 72- and 96-h-periods, arterial PCO2 (24 ± 4.4 Torr) and ventilatory frequency (105 ± 5 breaths min−1) stabilized, HCO3
− reached its apparent maximum (23.6 ± 0.0 mmol−1), glucose decreased by 32%, and pH increased significantly to 7.31 + 0.03. The return to normocapnia completely restored
arterial PCO2 (2.5 ± 0.14 Torr), HCO3
− (7.4 ± 0.59 mmol · l−1), ventilation frequency (71 ± 7 breaths · min−1), and pH (7.75 ± 0.04). Overall, hypercapnia produced a respiratory acidosis, hyperventilation, a transient norepinephrine
“spike”, and increased plasma catecholamines, cortisol, and arterial PO2. The respiratory acidosis was only partially compensated (35% pH restoration) 96 h after the onset of hypercapnia and resulted
in a significantly decreased blood-O2 affinity (Bohr effect), as determined by construction of in vitro blood O2 equilibrium curves at 15 °C and 20 °C. Prolonged exposure to hypercapnia may lead to acid-base disturbances and negatively
affect growth of white sturgeon.
Accepted: 17 August 1997 相似文献
9.
A number of nutritional factors influencing growth and glucose oxidase (EC 1.1.3.4) production by a newly isolated strain
of Penicillium pinophilum were investigated. The most important factors for glucose oxidase production were the use of sucrose as the carbon source,
and growth of the fungus at non-optimal pH 6.5. The enzyme was purified to apparent homogeneity with a yield of 74%, including
an efficient extraction step of the mycelium mass at pH 3.0, cation-exchange chromatography and gel filtration. The relative
molecular mass (M
r) of native glucose oxidase was determined to be 154 700 ± 4970, and 77 700 for the denatured subunit. Electron-microscopic
examinations revealed a sandwich-shaped dimeric molecule with subunit dimensions of 5.0 × 8.0 nm. Glucose oxidase is a glycoprotein
that contains tightly bound FAD with an estimated stoichiometry of 1.76 mol/mol enzyme. The enzyme is specific for d-glucose, for which a K
m value of 6.2 mM was determined. The pH optimum was determined in the range pH 4.0–6.0. Glucose oxidase showed high stability
on storage in sodium citrate (pH 5.0) and in potassium phosphate (pH 6.0), each 100 mM. The half-life of the activity was
considerably more than 305 days at 4 °C and 30 °C, and 213 days at 40 °C. The enzyme was unstable at temperatures above 40 °C
in the range pH 2.0–4.0 and at a pH above 7.0.
Received: 18 November 1996 / Received revision: 3 March 1997 / Accepted: 7 March 1997 相似文献
10.
The lipA gene, a structural gene encoding for protein of molecular mass 48 kDa, and lipB gene, encoding for a lipase-specific chaperone with molecular mass of 35 kDa, of Pseudomonas aeruginosa B2264 were co-expressed in heterologous host Escherichia coli BL21 (DE3) to obtain in vivo expression of functional lipase. The recombinant lipase was expressed with histidine tag at
its N terminus and was purified to homogeneity using nickel affinity chromatography. The amino acid sequence of LipA and LipB
of P. aeruginosa B2264 was 99–100% identical with the corresponding sequence of LipA and LipB of P. aeruginosa LST-03 and P. aeruginosa PA01, but it has less identity with Pseudomonas cepacia (Burkholderia cepacia) as it showed only 37.6% and 23.3% identity with the B. cepacia LipA and LipB sequence, respectively. The molecular mass of the recombinant lipase was found to be 48 kDa. The recombinant
lipase exhibited optimal activity at pH 8.0 and 37°C, though it was active between pH 5.0 and pH 9.0 and up to 45°C. K
m and V
max values for recombinant P. aeruginosa lipase were found to be 151.5 ± 29 μM and 217 ± 22.5 μmol min−1 mg−1 protein, respectively. 相似文献
11.
Improved Bioavailability of Poorly Water-Soluble Drug Curcumin in Cellulose Acetate Solid Dispersion
Curcumin (Cur), one of the most widely used natural active constituents with a great variety of beneficial biological and
pharmacological activities, is a practically water-insoluble substance with a short biologic half-life. The aim of this study
was to develop a sustained-release solid dispersion by employing water-insoluble carrier cellulose acetate for solubility
enhancement, release control, and oral bioavailability improvement of Cur. Solid dispersions were characterized by solubility,
in vitro drug release, Fourier transform infrared spectroscopy, X-ray diffractometry, and differential scanning calorimetry studies.
The in vivo performance was assessed by a pharmacokinetic study. Solid-state characterization techniques revealed the amorphous nature
of Cur in solid dispersions. Solubility/dissolution of Cur was enhanced in the formulations in comparison with pure drug.
Sustained-release profiles of Cur from the solid dispersions were ideally controlled in vitro up to 12 h. The optimized formulation provided an improved pharmacokinetic parameter (C
max = 187.03 ng/ml, t
max = 1.95 h) in rats as compared with pure drug (C
max = 87.06 ng/ml, t
max = 0.66 h). The information from this study suggests that the developed solid dispersions successfully enhanced the solubility
and sustained release of poorly water-soluble drug Cur, thus improving its oral bioavailability effectively. 相似文献
12.
Caroline Mirande Pascale Mosoni Christel Béra-Maillet Annick Bernalier-Donadille Evelyne Forano 《Applied microbiology and biotechnology》2010,87(6):2097-2105
A xylanase gene xyn10A was isolated from the human gut bacterium Bacteroides xylanisolvens XB1A and the gene product was characterized. Xyn10A is a 40-kDa xylanase composed of a glycoside hydrolase family 10 catalytic
domain with a signal peptide. A recombinant His-tagged Xyn10A was produced in Escherichia coli and purified. It was active on oat spelt and birchwood xylans and on wheat arabinoxylans. It cleaved xylotetraose, xylopentaose,
and xylohexaose but not xylobiose, clearly indicating that Xyn10A is a xylanase. Surprisingly, it showed a low activity against
carboxymethylcellulose but no activity at all against aryl-cellobioside and cellooligosaccharides. The enzyme exhibited K
m and V
max of 1.6 mg ml−1 and 118 μmol min−1 mg−1 on oat spelt xylan, and its optimal temperature and pH for activity were 37°C and pH 6.0, respectively. Its catalytic properties
(k
cat/K
m = 3,300 ml mg−1 min−1) suggested that Xyn10A is one of the most active GH10 xylanase described to date. Phylogenetic analyses showed that Xyn10A
was closely related to other GH10 xylanases from human Bacteroides. The xyn10A gene was expressed in B. xylanisolvens XB1A cultured with glucose, xylose or xylans, and the protein was associated with the cells. Xyn10A is the first family 10
xylanase characterized from B. xylanisolvens XB1A. 相似文献
13.
This article reports rate constants for thiol–thioester exchange (k
ex), and for acid-mediated (k
a), base-mediated (k
b), and pH-independent (k
w) hydrolysis of S-methyl thioacetate and S-phenyl 5-dimethylamino-5-oxo-thiopentanoate—model alkyl and aryl thioalkanoates, respectively—in water. Reactions such as
thiol–thioester exchange or aminolysis could have generated molecular complexity on early Earth, but for thioesters to have
played important roles in the origin of life, constructive reactions would have needed to compete effectively with hydrolysis
under prebiotic conditions. Knowledge of the kinetics of competition between exchange and hydrolysis is also useful in the
optimization of systems where exchange is used in applications such as self-assembly or reversible binding. For the alkyl
thioester S-methyl thioacetate, which has been synthesized in simulated prebiotic hydrothermal vents, k
a = 1.5 × 10−5 M−1 s−1, k
b = 1.6 × 10−1 M−1 s−1, and k
w = 3.6 × 10−8 s−1. At pH 7 and 23°C, the half-life for hydrolysis is 155 days. The second-order rate constant for thiol–thioester exchange
between S-methyl thioacetate and 2-sulfonatoethanethiolate is k
ex = 1.7 M−1 s−1. At pH 7 and 23°C, with [R″S(H)] = 1 mM, the half-life of the exchange reaction is 38 h. These results confirm that conditions
(pH, temperature, pK
a of the thiol) exist where prebiotically relevant thioesters can survive hydrolysis in water for long periods of time and
rates of thiol–thioester exchange exceed those of hydrolysis by several orders of magnitude. 相似文献
14.
U. Matrubutham J. E. Thonnard G. S. Sayler 《Applied microbiology and biotechnology》1997,47(5):604-609
Pseudomonas fluorescens HK44 is a bioluminescent bioreporter synthesizing light in the presence of naphthalene or salicylate. Upon immobilization,
HK44 is useful as an in situ or on-line biosensor of bioavailable naphthalene and salicylate in waste streams or contaminated
fields. The bioreporting efficacy of alginate/SrCl2-immobilized HK44 was investigated in simulated groundwater with different pH regimes. When induced with complex (salicylate
plus auxiliary energy supplements) and simple (salicylate as the sole energy supplement) inducer solutions, the specific light
response was steadier at pH 6 than at pH 7 in a 35-day study. There was no bioluminescence response from cells incubated in
groundwater samples with pH below 6. The rate of the luminescence reaction was stable at pH 6 irrespective of the type of
inducer solution, indicating the robust physiological status of the bioreporter bacteria. In addition, the quantity of light
synthesized was at least one order of magnitude higher with complex inducer solution than with simple inducer solution. The
numbers of viable and cultivable cells remained constant in groundwater at pH 6 and 7 (approx. 107 g−1 beads). The numbers decreased by four orders of magnitude (107 to 103) to zero in groundwaters with pH below 6. This study suggested that HK44 is useful for long-term biosensor applications in
moderately acidic to neutral groundwater conditions.
Received: 6 August 1996 / Received revision: 12 December 1996 / Accepted: 4 January 1997 相似文献
15.
Ethanol production by recombinant Escherichia coli strain FBR5 from dilute acid pretreated wheat straw (WS) by separate hydrolysis and fermentation (SHF) and simultaneous saccharification
and fermentation (SSF) was studied. The yield of total sugars from dilute acid (0.5% H2SO4) pretreated (160 °C, 10 min) and enzymatically saccharified (pH 5.0, 45 °C, 72 h) WS (86 g/l) was 50.0 ± 1.4 g/l. The hydrolyzate
contained 1,184 ± 19 mg furfural and 161 ± 1 mg hydroxymethyl furfural per liter. The recombinant E. coli FBR5 could not grow at all at pH controlled at 4.5 to 6.5 in the non-abated wheat straw hydrolyzate (WSH) at 35 °C. However,
it produced 21.9 ± 0.3 g ethanol from non-abated WSH (total sugars, 44.1 ± 0.4 g/l) in 90 h including the lag time of 24 h
at controlled pH 7.0 and 35 °C. The bioabatement of WS was performed by growing Coniochaeta ligniaria NRRL 30616 in the liquid portion of the pretreated WS aerobically at pH 6.5 and 30 °C for 15 h. The bacterium produced 21.6 ± 0.5 g
ethanol per liter in 40 h from the bioabated enzymatically saccharified WSH (total sugars, 44.1 ± 0.4 g) at pH 6.0. It produced
24.9 ± 0.3 g ethanol in 96 h and 26.7 ± 0.0 g ethanol in 72 h per liter from bioabated WSH by batch SSF and fed-batch SSF,
respectively. SSF offered a distinct advantage over SHF with respect to reducing total time required to produce ethanol from
the bioabated WS. Also, fed-batch SSF performed better than the batch SSF with respect to shortening the time requirement
and increase in ethanol yield. 相似文献
16.
Juozas Kulys Kastis Krikstopaitis Arturas Ziemys 《Journal of biological inorganic chemistry》2000,5(3):333-340
N -substituted phenothiazines (PTs) and phenoxazines (POs) catalyzed by fungal Coprinus cinereus peroxidase and Polyporus pinsitus laccase were investigated at pH 4–10. In the case of peroxidase, an apparent bimolecular rate constant (expressed as k
cat/K
m) varied from 1 ×107 M−1 s−1to 2.6×108 M−1 s−1 at pH 7.0. The constants for PO oxidation were higher in comparison to PT. pH dependence revealed two or three ionizable
groups with pK
a values of 4.9–5.7 and 7.7–9.7 that significantly affected the activity of peroxidase. Single-turnover experiments showed
that the limiting step of PT oxidation was reduction of compound II and second-order rate constants were obtained which were
consistent with the constants at steady-state conditions. Laccase-catalyzed PT and PO oxidation rates were lower; apparent
bimolecular rate constants varied from 1.8×105 M−1 s−1 to 2.0×107 M−1 s−1 at pH 5.3. PO constants were higher in comparison to PT, as was the case with peroxidase. The dependence of the apparent
bimolecular constants of compound II or copper type 1 reduction, in the case of peroxidase or laccase, respectively, was analyzed
in the framework of the Marcus outer-sphere electron-transfer theory. Peroxidase-catalyzed reactions with PT, as well as PO,
fitted the same hyperbolic dependence with a maximal oxidation rate of 1.6×108 M−1 s−1 and a reorganization energy of 0.30 eV. The respective parameters for laccase were 5.0×107 M−1 s−1 and 0.29 eV.
Received: 20 September 1999 / Accepted: 24 February 2000 相似文献
17.
Patricia A. M. Williams Juan Zinczuk Enrique J. Baran 《Biological trace element research》2010,134(2):220-225
The interaction of the VO2+ cation with the monoisoamyl ester of meso-2,3-dimercaptosuccinic acid (MiADMSA) was investigated by electron absorption spectroscopy in aqueous solutions at different
pH values. The spectral behavior, complemented with a spectrophotometric titration, shows the generation of a [VO(MiADMSA)2]4− complex in which the oxocation interacts with two pairs of deprotonated –SH groups of the ester. Besides, MiADMSA rapidly
reduces VO3− to VO2+, which might be chelated by an excess of the ester, and also produces relatively rapid reduction of V2O5 suspensions at pH = 6.5. The results of this study suggest that MiADMSA might be a potentially useful detoxification agent
for vanadium. 相似文献
18.
The biodegradation of tributyl phosphate (Bu3-P, TBP), releasing phosphate at a high enough concentration locally to precipitate uranium from solution, was demonstrated
by a mixed culture consisting primarily of pseudomonads. The effect of various parameters on Bu3-P biodegradation by growing cells is described. Growth at the expense of Bu3-P as the carbon and phosphorus source occurred over a pH range from 6.5 to 8, and optimally at pH 7. Bu3-P biodegradation was optimal at 30 °C, reduced at 20 °C and negligible at 4 °C and 37 °C. Incorporation of Cu or Cd inhibited,
and Ni, Co and Mn reduced its degradation. Inorganic phosphate (above 10 mM) and kerosene (up to 1 g/l) reduced Bu3-P biodegradation significantly, but nitrate had no effect. Sulphate (10–100 mM) was inhibitory. When pregrown biomass was used
the fastest rates of tributyl and dibutyl phosphate biodegradation were 25 μmol h−1 mg protein−1 and 37 μmol h−1 mg protein−1 respectively. Microcarrier-immobilised biomass decontaminated uranium-bearing acid mine waste water by uranium phosphate
precipitation at the expense of Bu3-P hydrolysis in the presence of 35 mM SO4
2−. At pH 4.5, 79% of the UO2
2+ was removed at a flow rate of 1.4 ml/h on a 7-ml test column.
Received: 2 June 1997 / Received revision: 15 September 1997 / Accepted: 19 September 1997 相似文献
19.
G. R. V. Babu O. K. Vijaya V. L. Ross J. H. Wolfram K. D. Chapatwala 《Applied microbiology and biotechnology》1996,45(1-2):273-277
Our isolate, Pseudomonas putida, is known to be capable of utilizing cyanides as the sole source of carbon (C) and nitrogen (N) both in the form of free cells
and cells immobilized in calcium alginate. In the present study, the cell-free extract(s) were prepared from the cells of
P. putida grown in the presence of sodium cyanide. The ability of enzyme(s) to convert cyanides, cyanates, thiocyanates, formamide and
cyanide-containing mine waters into ammonia (NH3) was studied at pH 7.5 and pH 9.5. The kinetic analysis of cyanide and formamide conversion into NH3 at pH 7.5 and pH 9.5 by the cell-free extract(s) of P. putida was also studied. The K
m and V
max values for cyanide/formamide were found to be 4.3/8 mM and 142/227 μmol NH3 released mg protein-1 min-1 respectively at pH 7.5 and 5/16.67 mM and 181/434 μmol NH3 released mg protein-1 h-1 respectively at pH 9.5. The study thus concludes that the cell-free extract(s) of P. putida is able to metabolize not only cyanides, cyanates, thiocyanates, and formamide but also cyanide-containing mine waters to
NH3.
Received: 10 April 1995/Received revision: 24 July 1995/Accepted: 22 August 1995 相似文献
20.
Acinetobacter sp. XMZ-26 (ACCC 05422) was isolated from soil samples obtained from glaciers in Xinjiang Province, China. The partial nucleotide
sequence of a lipase gene was obtained by touchdown PCR using degenerate primers designed based on the conserved domains of
cold-adapted lipases. Subsequently, a complete gene sequence encoding a 317 amino acid polypeptide was identified. Our novel
lipase gene, lipA, was overexpressed in Escherichia coli. The recombinant protein (LipA) was purified by Ni-affinity chromatography, and then deeply characterised. The LipA resulted
to hydrolyse pNP esters of fatty acids with acyl chain length from C2 to C16, and the preferred substrate was pNP octanoate showing a k
cat = 560.52 ± 28.32 s−1, K
m = 0.075 ± 0.008 mM, and a k
cat/K
m = 7,377.29 ± 118.88 s−1 mM−1. Maximal LipA activity was observed at a temperature of 15°C and pH 10.0 using pNP decanoate as substrate. That LipA peaked at such a low temperature and remained most activity between 5°C and 35°C indicated
that it was a cold-adapted enzyme. Remarkably, this lipase retained much of its activity in the presence of commercial detergents
and organic solvents, including Ninol, Triton X-100, methanol, PEG-600, and DMSO. This cold-adapted lipase may find applications
in the detergent industry and organic synthesis. 相似文献