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1.
Inhibition of microbial xylitol production by acetic acid and its relation with fermentative parameters 总被引:5,自引:0,他引:5
Precipitated sugarcane bagasse hemicellulosic hydrolysate containing acetic acid was fermented by Candida guilliermondii FTI 20037 under different operational conditions (pH 4.0 and 7.0, three aeration rates). At pH 7.0 and k
L
a of 10 (0.75 vvm) and 22.5/h (3.0 vvm) the acetic acid had not been consumed until the end of the fermentations, whereas at
the same pH and k
L
a of 35/h (4.5 vvm) the acid was rapidly consumed and acetic acid inhibition was not important. On the other hand, fermentations
at an initial pH of 4.0 and k
L
a of 22.5 and 35/h required less time for the acid uptake than fermentations at k
L
a of 10/h. The acetic acid assimilation by the yeast indicates the ability of this strain to ferment in partially detoxified
medium, making possible the utilization of the sugarcane bagasse hydrolysate in this bioprocess. The effects on xylitol yield
and production are reported. 相似文献
2.
Four myrosinase (β-thioglucosidase EC. 3.2.3.1) and seven disaccharase (β-fructofuranosidase, EC. 3.2.1.26) isoenzymes were isolated from turnip leaves. The most active enzymes were isolated in pure
form. Myrosinase and disaccharase mol wt was 62.0 × 103 and 69.5 × 103 dalton, respectively, on the basis of gel filtration on Sephadex G-200.
Myrosinase pH profile showed high activity between pH 5 and 7 with the optimum at pH 5.5. The purified enzyme was heat-stable
for 60 min at 30°C with only loss of 24% of activity. Its activity is strongly inhibited (100%) by Pb2+, Ba2+, Cu2+ and Ca2+ ions, and activated (70%) by EDTA at 0.04M. The pure enzyme failed to hydrolyze amylose, glycogen, lactose, maltose, and
sucrose. TheK
m andV
max values of myrosinase using sinigrin as specific substrate was 0.045 mM and 2.5 U, respectively.
The maximal activity of disaccharase enzyme was obtained at pH 4–5 and 35–37°C. The enzyme was heat-stable at 30°C for 30
min with only 10% loss of its activity. Its activity is strongly activated (70–240%) by Ca2+, Ba2+, Cu2+, and EDTA at 0.01M. The enzyme activity is specific to the disaccharide sucrose and failed to hydrolyze other disaccharides (maltose and lactose).
TheK
m andV
max of disaccharase were 0.123 mM and 3.33 U, respectively. 相似文献
3.
Lee Ju-No Lee Jin-Suk Shin Chul-Seung Park Soon-Chul Kim Seung-Wook 《Applied biochemistry and biotechnology》2000,84(1-9):329-342
Possible methods to minimize the toxic effects of SO
x
and NO
x
on the growth of a highly CO2 tolerant and fast-growing microalga, Chlorella sp. KR-1, were investigated. Maintaining the pH of the culturing media at an adequate value was quite important to enhancing
the tolerances of the microalgae to SO
x
and NO
x
. Controlling the pH by adding an alkaline solution, using a low flow rate of gas fed to the culture, and using a high concentration
of inoculating cells were effective methods to maintaining the proper pH of the culture. Controlling the pH was the most effective
method but could be applied only for some specific microalgae. 相似文献
4.
pH and temperature play critical roles in multistep enzymatic conversions. In such conversions, the optimal pH for individual
steps differs greatly. In this article, we describe the production of glucoamylase (from Aspergillus oryzae MTCC152 in solid-state fermentation) and glucose isomerase (from Streptomyces griseus NCIM2020 in submerged fermentation), used in industries for producing high-fructose syrup. Optimum pH for glucoamylase was
found to be 5.0. For glucose isomerase, the optimum pH ranged between 7.0 and 8.5, depending on the type of buffer used. Optimum
temperature for glucoamylase and glucose isomerase was 50 and 60°C, respectively. When both the enzymatic conversions were
performed simultaneously at a compromised pH of 6.5, both the enzymes showed lowered activity. We also studied the kinetics
at different pHs, which allows the two-step reaction to take place simultaneously. This was done by separating two steps by
a thin layer of urease. Ammonia generated by the hydrolysis of urea consumed the hydrogen ions, thereby allowing optimal activity
of glucose isomerase at an acidic pH of 5.0. 相似文献
5.
A synchrotron FTIR microspectroscopy investigation of fungal hyphae grown under optimal and stressed conditions 总被引:1,自引:0,他引:1
Synchrotron FTIR can provide high spatial resolution (<10 μm pixel size) in situ biochemical analyses of intact biotissues,
an area of increasing importance in the post-genomic era, as gene functions and gene networks are coming under direct scrutiny.
With this technique, we can simultaneously assess multiple aspects of cell biochemistry and cytoplasmic composition. In this
paper, we report the first results of our synchrotron FTIR examination of hyphae of three important fungal model systems,
each with sequenced genomes and a wealth of research: Aspergillus, Neurospora, and Rhizopus. We have analyzed the FTIR maps of Aspergillus nidulans cells containing the hypA1 allele, a well-characterized single-gene temperature-sensitive morphogenetic mutation. The hypA1 cells resemble wildtype at 28 °C but have growth defects at 42 °C. We have also investigated Neurospora and Rhizopus cultures grown in media with optimal or elevated pH. Significant differences between the spectra of the three fungi are likely
related to differences in composition and structure. In addition, high spatial resolution synchrotron FTIR spectroscopy provides
an outstanding method for monitoring subtle subcellular changes that accompany environmental stress.
Figure Photomicrographs and FTIR spectra acquired along Rhizopus hyphae grown at pH 6.5 (a) and pH 8.5 (b). Scale bars 50 μm 相似文献
6.
Effects of pH and Temperature on Recombinant Manganese Peroxidase Production and Stability 总被引:1,自引:0,他引:1
Jiang F Kongsaeree P Schilke K Lajoie C Kelly C 《Applied biochemistry and biotechnology》2008,146(1-3):15-27
The enzyme manganese peroxidase (MnP) is produced by numerous white-rot fungi to overcome biomass recalcitrance caused by
lignin. MnP acts directly on lignin and increases access of the woody structure to synergistic wood-degrading enzymes such
as cellulases and xylanases. Recombinant MnP (rMnP) can be produced in the yeast Pichia pastoris αMnP1-1 in fed-batch fermentations. The effects of pH and temperature on recombinant manganese peroxidase (rMnP) production
by P. pastoris αMnP1-1 were investigated in shake flask and fed-batch fermentations. The optimum pH and temperature for a standardized fed-batch
fermentation process for rMnP production in P. pastoris αMnP1-1 were determined to be pH 6 and 30 °C, respectively. P. pastoris αMnP1-1 constitutively expresses the manganese peroxidase (mnp1) complementary DNA from Phanerochaete chrysosporium, and the rMnP has similar kinetic characteristics and pH activity and stability ranges as the wild-type MnP (wtMnP). Cultivation
of P. chrysosporium mycelia in stationary flasks for production of heme peroxidases is commonly conducted at low pH (pH 4.2). However, shake
flask and fed-batch fermentation experiments with P. pastoris αMnP1-1 demonstrated that rMnP production is highest at pH 6, with rMnP concentrations in the medium declining rapidly at
pH less than 5.5, although cell growth rates were similar from pH 4–7. Investigations of the cause of low rMnP production
at low pH were consistent with the hypothesis that intracellular proteases are released from dead and lysed yeast cells during
the fermentation that are active against rMnP at pH less than 5.5. 相似文献
7.
A. Amini V. Barclay T. Rundlöf S. Jönsson A. Karlsson T. Arvidsson 《Chromatographia》2006,63(3-4):143-148
This paper reports the determination of caffeine, ephedrine and pseudo-ephedrine in a dietary product by two rapid and simple
methods utilising capillary electrophoresis (CE). The solutes were extracted from the product using 0.2 M HCl and determined
by CE with background electrolytes containing 7.5% highly sulfated-β-cyclodextrin (7–11 sulfate groups per β-CD molecule) at pH 2.5 and pH 7.6. Determination of ephedrine and pseudo-ephedrine was accomplished at pH 2.5 with the anode
at the detection side of the capillary whereas caffeine was quantified at pH 7.6 with a normal electrophoresis polarity mode.
Triethanolamine was added to the running buffer at pH 2.5 in order to reverse the electroosmotic flow (EOF) and thereby speed
up the separation of ephedrine and pseudo-ephedrine.
Revised: 18 November 2005 and 2 January 2006 相似文献
8.
Penna Thereza Christina Vessoni Chiarini Eb Machoshvili Irene Alexeevna Ishii Marina Pessoa Adalberto 《Applied biochemistry and biotechnology》2002,98(1-9):791-802
The recombinant green fluorescent protein (gfp
uv
) was expressed by Escherichia coli DH5-α cells transformed with the plasmid pGFPuv. The gfp
uv
was selectively permeabilized from the cells in buffer solution (25 mM Tris-HCl, pH 8.0), after freezing (−70°C for 15 h), by four freeze (−20°C)/thaw cycles interlaid by sonication. The average
content of released gfp
uv
(experiment 2) was 7.76, 34.58, 39.38, 12.90, and 5.38%, for the initial freezing (−70°C) and the first, second, third and
fourth freeze/thaw cycles, respectively. Superfusion on freezing was observed between −11°C and −14°C, after which it reached
−20°C at 0.83°C/min. 相似文献
9.
5,10,15,20-tetrakis(phenoxy acetic acid) porphyrin (PAAP) was covalently linked to Merrifield chloromethylated resin. Characterization
of PAAP and the modified polymeric matrix were performed by 1H NMR, FTIR and elemental analysis. The sorbent was used for the separation and enrichment of the d-electron metals (Mn(II), Co(II), Ni(II), Cu(II) and Zn(II)) at pH 6–8 and of the f-electron metals U(VI) and Th(IV) at pH 4–5. The metals ions were preconcentrated with a concentration factor range of 115–215
and then determined by flame atomic absorption spectrometry or visible spectrophotometry using Arsenazo(III). The retained
metals were eluted with 2.0 mol L−1 HNO3 in the case of the d-electron metals and 0.1/0.25 mol L−1 HCl in the case of the f-electron metals. The procedure was validated by analyzing the NIST standard reference material 2709 (San Joaquin Soil).
Correspondence: Melek Merdivan, Chemistry Department, Faculty of Arts and Sciences, Dokuz Eylul University, 35160 Buca, Izmir,
Turkey 相似文献
10.
Microorganisms producing lipase were isolated from soil and sewage samples and screened for enantioselective resolution of
(R,S)-methyl mandelate to (R)-mandelic acid. A strain designated as GXU56 was obtained and identified as Burkholderia sp. Preparing immobilized GXU56 lipase by simple adsorption on octyl sepharose CL-4B, the optimum temperature was shifted
from 40 °C (free lipase) to 50 °C (immobilized lipase), and the optimum pH was shifted from 8.0 (free lipase) to 7.2 (immobilized
lipase). The immobilized enzyme displayed excellent stability in the pH range of 5.0–8.0, at the temperatures below 50 °C
and in organic solvents compared with free enzyme. Enantioselectivity ratio for (R)-mandelic acid (E) was dramatically improved from 29.2 to more than 300 by applying immobilized lipase in the resolution of (R,S)-methyl mandelate. After five cycles of use of immobilized lipase, conversion and enantiomeric excess of (R)-mandelic acid were 34.5% and 98.5%, respectively, with enantioselectivity ratio for (R)-mandelic acid (E) of 230. Thus, octyl-sepharose-immobilized GXU56 lipase can be used as a bio-resolution reagent for producing (R)-mandelic acid. 相似文献
11.
The extraction characteristics of some selected metals from an aqueous buffered solution by LIX51. a fluorinated commercial
β-diketone extractant, have been investigated. The pH 1/2 (pH at which 50% of the metal ion is extracted) and the logK
ex
values for the extracted metals by 5% (v/v) L1X51 in methylisobutylkctone(MIBK) have been obtained. The order of extraction
of metals with LIX51 as a function of pH 1/2 value is: Cu(II) < Pd(II) < Co(II) < Zn(II) < Fe(H) < Ph(II) < Mn(II) < Cd(II)
< Ni(II). 相似文献
12.
Xylanase from Bacillus pumilus strain MK001 was immobilized on different matrices following varied immobilization methods. Entrapment using gelatin (GE)
(40.0%), physical adsorption on chitin (CH) (35.0%), ionic binding with Q-sepharose (Q-S) (45.0%), and covalent binding with
HP-20 beads (42.0%) showed the maximum xylanase immobilization efficiency. The optimum pH of immobilized xylanase shifted
up to 1.0 unit (pH 7.0) as compared to free enzyme (pH 6.0). The immobilized xylanase exhibited higher pH stability (up to
28.0%) in the alkaline pH range (7.0–10.0) as compared to free enzyme. Optimum temperature of immobilized xylanase was observed
to be 8 °C higher (68.0 °C) than free enzyme (60.0 °C). The free xylanase retained 50.0% activity, whereas xylanase immobilized
on HP-20, Q-S, CH, and GE retained 68.0, 64.0, 58.0, and 57.0% residual activity, respectively, after 3 h of incubation at
80.0 °C. The immobilized xylanase registered marginal increase and decrease in K
m and V
max values, respectively, as compared to free enzyme. The immobilized xylanase retained up to 70.0% of its initial hydrolysis
activity after seven enzyme reaction cycles. The immobilized xylanase was found to produce higher levels of high-quality xylo-oligosaccharides
from birchwood xylan, indicating its potential in the nutraceutical industry. 相似文献
13.
Baumler DJ Hung KF Bose JL Vykhodets BM Cheng CM Jeong KC Kaspar CW 《Applied biochemistry and biotechnology》2006,134(1):15-26
A portion of the cbpA gene from Escherichia coli K-12 encoding a 24 amino acid proton-buffering peptide (Pbp) was cloned via the shuttle vector pJB99 into E. coli JM105 and subsequently into Zymomonas mobilis CP4. Expression of Pbp was confirmed in both JM105 and CP4 by HPLC. Z. mobilis CP4 carrying pJB99-2 (Pbp) exhibited increased acid tolerance (p<0.05) in acidified TSB (HCl [pH 3.0] or acetic acid [pH 3.5]), glycine-HCl buffer (pH 3.0), and sodium acetate-acetic acid
buffer (pH 3.5) in comparison to the parent strain (CP4) and CP4 with pJB99 (control plasmid). Although the expression of
Pbp influenced survival at a low pH, the minimum growth pH was unaffected. Growth of Z. mobilis in the presence of ampicillin also significantly increased acid tolerance by an unknown mechanism. Results from this study
demonstrate that the production of a peptide with a high proportion of basic amino acids can contribute to protection from
low pH and weak organic acids such as acetic acid. 相似文献
14.
Polytetrafluoroethylene (PTFE) was grafted (g) with acrylic acid (AAc) by γ-ray pre-irradiation method to get PTFE-g-AAc films, then N-isopropylacrylamide (NIPAAm) was grafted onto PTFE-g-AAc films with γ-ray to get (PTFE-g-AAc)-g-NIPAAm. PTFE films were irradiated in air at a dose rate of 3.0 kGy h–1 and different radiation dose. The irradiated films were placed in glass ampoules, which contained aqueous solutions with different monomer concentration (AAc), and then they were heated at different temperatures and reaction time. NIPAAm onto PTFE-g-AAc was carried out with the same procedure with monomer concentration of 1 mol L−1. The thermosensitivity of the samples was defined and calculated as the ratio of the grafted samples swelling at 28 and 35 °C, and pH sensitivity defined as the ratio of the grafted samples swelling at pH 2 and 8. 相似文献
15.
研究了β-环糊精衍生化胰酶的合成以及作为毛细管电色谱手性选择剂的分离性能. 利用乙二醇二环氧丙烷醚作为交联剂, 将β-环糊精接枝到胰酶蛋白的主链, 得到了β-环糊精衍生化胰酶. 将其通过化学键合连接到毛细管柱内壁, 制备了β-环糊精衍生化胰酶毛细管电色谱柱. 在加压毛细管电色谱模式下, 利用该柱分离了色氨酸、扑尔敏、布洛芬、异丙嗪和阿托品等对映异构体, 得到了理想的分离效果, 且在分离扑尔敏时, 随着电压的增加, 对映异构体分离的分离度和相对保留时间均增加. 相似文献
16.
Functional expression of a β-d-1,4 glucanase-encoding gene (egl1) from a filamentous fungus was achieved in both Escherichia coli and Saccharomyces cerevisiae using a modified version of pRS413. Optimal activity of the E. coli-expressed enzyme was found at incubation temperatures of 60°C, whereas the enzyme activity was optimal at 40°C when expressed
by S. cerevisiae. Enzyme activity at different pH levels was similar for both bacteria and yeast, being highest at 5.0. Yeast expression resulted
in a highly glycosylated protein of approx 60 kDa, compared to bacterial expression, which resulted in a protein of 30 kDa.
The hyperglycosylated protein had reduced enzyme activity, indicating that E. coli is a preferred vehicle for production scale-up. 相似文献
17.
A new zirconia-based stationary phase (DPZ) was prepared by modifying zirconia with dodecylamine-N,N-dimethylenephosphonic acid (DDPA). DDPA was adsorbed on zirconia with only one phosphonic group, with the other being free.
Besides the hydrophobic interaction provided by nonpolar dodecyl, DPZ also has dipolar interaction, ion-exchange or electrostatic
repellent interaction provided by the free phosphonic group and amino group at different conditions. Separation of bases on
this stationary phase was achieved with satisfaction owing to the various retention mechanisms. The influence of methanol
content, pH value, ion types, and ionic strength of mobile phase are studied in detail.
Translated from Chinese Journal of Chromatography, 2005, 23(1) (in Chinese) 相似文献
18.
De Araújo Álvaro Alberto Roussos Sevastianos 《Applied biochemistry and biotechnology》2002,98(1-9):311-318
A technique was established to study ectomycorrhizal fungi on agar media. Petri dishes, 60 mm in diameter, containing 10 mL
of culture medium covered with a cellophane disk were used for easy collection of the mycelium after growth. For analysis
of fungal biomass production, a sterilized cellophane sheet was placed on the medium’s surface. Inoculation was achieved by
placing a mycelial block onto the center of the cellophane sheet and then incubating at 25°C in the dark. Colony radial growth
was measured and biomass dry wt was determined. Fresh mycelia were homogenized with 10 mL of acetate buffer (pH 5.5) for enzyme
analysis. A crude extract was obtained by adding all culture medium to 90 mL of distilled water and homogenizing in a Potter.
Reducing sugars, enzyme concentration, and pH were determined. Three fungal strains, Suillus collinitus, Pisosithus arrhizus, and Hebeloma cylindrosporum, were grown in different culture media (potato dextrose agar or Pintro’s medium). Parameters measured over time included
glucose concentration, phosphatase activity, biomass, and pH. 相似文献
19.
Evert J. Elzinga Yuanzhi Tang Jason McDonald Stephanie DeSisto Richard J. Reeder 《Journal of colloid and interface science》2009,340(2):153-159
The interaction of selenate, selenite, and chromate with the hydrated surface of γ-Al2O3 was studied using a combination of macroscopic pH edge data, electrophoretic mobility measurements, and X-ray absorption spectroscopic analyses. The pH edge data show generally increased oxyanion adsorption with decreasing pH, and indicate ionic strength-(in)dependent adsorption of chromate and selenate across the pH range 4–9, and ionic strength-(in)dependent adsorption of selenite in this pH range. The adsorption of chromate peaks at pH 5.0, whereas for selenate and selenite no pH adsorption maxima are observed. Electrophoretic mobility measurements show that all three oxyanions decrease the zeta potential of γ-Al2O3 upon adsorption; however, only selenite decreased the pHPZC of the γ-Al2O3 sorbent. EXAFS data indicate that selenite ions are coordinated in a bridging bidentate fashion to surface AlO6 octahedra, whereas no second-neighbor Al scattering was observed for adsorbed selenate ions. Combined, the results presented here show that pH is a major factor in determining the extent of adsorption of selenate, selenite, and chromate on hydrated γ-Al2O3. The results point to substantial differences between these anions as to the mode of adsorption at the hydrated γ-Al2O3 surface, with selenate adsorbing as nonprotonated outer-sphere complexes, chromate forming a mixture of monoprotonated and nonprotonated outer-sphere adsorption complexes, and selenite coordinating as inner-sphere surface complexes in bridging configuration. 相似文献
20.
Marcio José Tiera Gerson Rodrigues dos Santos Vera A. de Oliveira Tiera Neide Aparecida Blaz Vieira Elisabete Frolini Rodrigo C. da Silva Watson Loh 《Colloid and polymer science》2005,283(6):662-670
A series of N-isopropylacrylamide (NIPAM)-acrylic acid–ethyl methacrylate terpolymers with varied monomer compositions was prepared by radical polymerization. The solution behavior of these polymers was studied in dilute aqueous solution using spectrophotometry, fluorescence spectroscopy and high-sensitivity differential scanning calorimetry. The results obtained revealed that the lower critical solution temperatures depend strongly on the copolymer composition, solution pH and ionic strength. At a high pH, the ionization of acrylic acid (AA) units leads to an increase in solution cloud points (Tc). Solutions of polymers containing 10% or less of AA display a constant Tc for pH above 5.5, with 15% there is a continuous increase in Tc with pH and, for higher AA contents, no clouding was observed within the studied temperature range. Fluorescence probe studies were conducted by following the I 1/I 3 ratio of pyrene vibronic bands and the emission of anilinonaphtalene sulfonic acid, sodium salt (ANS), both approaches revealing the existence of hydrophobic domains for polymers with higher ethyl methacrylate content at temperatures lower than Tc, suggesting some extent of aggregation and/or a coil-to-globule transition. Scanning calorimetry measurements showed an endothermic transition at temperatures agreeing with the previously detected cloud points. Moreover, the transition curves became broader and with a smaller transition enthalpy, as both the AA content and the solution pH were increased. These broader transitions were interpreted to be the result of a wider molecular distribution upon polymer ionization, hence, displaying varied solution properties. The decrease in transition enthalpy was rationalized as a consequence of reminiscent hydration of NIPAM units, even after phase separation, owing to the presence of electric charges along the polymer chain. 相似文献