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1.
K+-conductive pathways were evaluated in isolated surface and crypt colonic cells, by measuring 86Rb efflux. In crypt cells, basal K+ efflux (rate constant: 0.24 ± 0.044 min−1, span: 24 ± 1.3%) was inhibited by 30 mM TEA and 5 mM Ba2+ in an additive way, suggesting the existence of two different conductive pathways. Basal efflux was insensitive to apamin,
iberiotoxin, charybdotoxin and clotrimazole. Ionomycin (5 μM) stimulated K+ efflux, increasing the rate constant to 0.65 ± 0.007 min−1 and the span to 83 ± 3.2%. Ionomycin-induced K+ efflux was inhibited by clotrimazole (IC50 of 25 ± 0.4 μM) and charybdotoxin (IC50 of 65 ± 5.0 nM) and was insensitive to TEA, Ba2+, apamin and iberiotoxin, suggesting that this conductive pathway is related to the Ca2+-activated intermediate-conductance K+ channels (IKca). Absence of extracellular Ca2+ did neither affect basal nor ionomycin-induced K+ efflux. However, intracellular Ca2+ depletion totally inhibited the ionomycin-induced K+ efflux, indicating that the activation of these K+ channels mainly depends on intracellular calcium liberation. K+ efflux was stimulated by intracellular Ca2+ with an EC50 of 1.1 ± 0.04 μM. In surface cells, K+ efflux (rate constant: 0.17 ± 0.027 min−1; span: 25 ± 3.4%) was insensitive to TEA and Ba2+. However, ionomycin induced K+ efflux with characteristics identical to that observed in crypt cells. In conclusion, both surface and crypt cells present
IKCa channels but only crypt cells have TEA- and Ba2+-sensitive conductive pathways, which would determine their participation in colonic K+ secretion. 相似文献
2.
Giuseppa Augello Roberto Puleio Maria Rita Emma Antonella Cusimano Guido R. Loria James A. McCubrey 《Cell cycle (Georgetown, Tex.)》2016,15(4):573-583
Phosphatase and tensin homolog (PTEN) gene is considered a tumor suppressor gene. However, PTEN mutations rarely occur in hepatocellular carcinoma (HCC), whereas heterozygosity of PTEN, resulting in reduced PTEN expression, has been observed in 32–44% of HCC patients. In the present study, we investigated the effects of the small molecule PTEN inhibitor VO-OHpic in HCC cells. VO-OHpic inhibited cell viability, cell proliferation and colony formation, and induced senescence-associated β-galactosidase activity in Hep3B (low PTEN expression) and to a lesser extent in PLC/PRF/5 (high PTEN expression) cells, but not in PTEN-negative SNU475 cells. VO-OHpic synergistically inhibited cell viability when combined with PI3K/mTOR and RAF/MEK/ERK pathway inhibitors, but only in Hep3B cells, and significantly inhibited tumor growth in nude mice bearing xenografts of Hep3B cells. Therefore, we demonstrated for the first time that VO-OHpic inhibited cell growth and induced senescence in HCC cells with low PTEN expression, and that the combination of VO-OHpic with PI3K/mTOR and RAF/MEK/ERK inhibitors resulted in a more effective tumor cell kill. Our findings, hence, provide proof-of-principle evidence that pharmacological inhibition of PTEN may represent a promising approach for HCC therapy in a subclass of patients with a low PTEN expression. 相似文献
3.
Dominic D. W. S. Wong Victor J. Chan Amanda A. McCormack Sarah B. Batt 《Applied microbiology and biotechnology》2010,86(5):1463-1471
A novel xyloglucan-specific endo-β-1,4-glucanase gene (xeg5A) was isolated, cloned, and expressed in Esherichia coli. The enzyme XEG5A consisted of a C-terminal catalytic domain and N-terminal sequence of ~90 amino acid residues with unknown
function. The catalytic domain assumed an (α/β)8-fold typical of glycoside hydrolase (GH) family 5, with the two catalytic residues Glu240 and Glu362 located on opposite
sides of the surface groove of the molecule. The recombinant enzyme showed high specificity towards tamarind xyloglucan and
decreasing activity towards xyloglucan oligosaccharide (HDP-XGO), carboxymethyl cellulose, and lichenan. Tamarind xyloglucan
was hydrolyzed to three major fragments, XXXG, XXLG/XLXG, and XLLG. The hydrolysis followed the Michaelis–Menten kinetics,
yielding K
m and V
max of 3.61 ± 0.23 mg/ml and 0.30 ± 0.01 mg/ml/min, respectively. However, the hydrolysis of HDP-XGO showed a decrease in the
rate at high concentrations suggesting appearance of excess substrate inhibition. The addition of XXXG resulted in linear
noncompetitive inhibition on the hydrolysis of tamarind xyloglucan giving a K
i of 1.46 ± 0.13 mM. The enzyme was devoid of transglycosylase activities. 相似文献
4.
Ribitsch D Karl W Wehrschütz-Sigl E Tutz S Remler P Weber HJ Gruber K Stehr R Bessler C Hoven N Sauter K Maurer KH Schwab H 《Applied microbiology and biotechnology》2009,81(5):875-886
In the course of a microbial screening of soil samples for new oxidases, different enrichment strategies were carried out.
With choline as the only carbon source, a microorganism was isolated and identified as Arthrobacter nicotianae. From this strain, a gene coding for a choline oxidase was isolated from chromosomal DNA. This gene named codA was cloned in Escherichia coli BL21-Gold and the protein (An_CodA) heterologously overexpressed as a soluble intracellular protein of 59.1 kDa. Basic biochemical characterization of
purified protein revealed a pH optimum of 7.4 and activity over a broad temperature range (15–70 °C). Specific activities
were determined toward choline chloride (4.70 ± 0.12 U/mg) and the synthetic analogs bis(2-hydroxyethyl)-dimethylammonium
chloride (0.05 ± 0.45 × 10–2 U/mg) and tris-(2-hydroxyethyl)-methylammonium methylsulfate (0.01 ± 0.12 × 10–2 U/mg). With increasing number of oxidizable groups, a significant decrease in activity was noted. Determination of kinetic
parameters in atmorspheric oxygen resulted in K
M = 1.51 ± 0.09 mM and V
max = 42.73 ± 0.42 mU/min for choline chloride and K
M = 4.77 ± 0.76 mM and V
max = 48.40 ± 2.88 mU/min for the reaction intermediate betaine aldehyde respectively. Nuclear magnetic resonance spectroscopic
analysis of the products formed during the enzyme reaction with choline chloride showed that in vitro the intermediate betaine
aldehyde exists also free in solution. 相似文献
5.
Localization of ion-regulatory epithelia in embryos and hatchlings of two cephalopods 总被引:1,自引:0,他引:1
Marian Y. Hu Elliott Sucré Mireille Charmantier-Daures Guy Charmantier Magnus Lucassen Nina Himmerkus Frank Melzner 《Cell and tissue research》2010,339(3):571-583
The tissue distribution and ontogeny of Na+/K+-ATPase has been examined as an indicator for ion-regulatory epithelia in whole animal sections of embryos and hatchlings
of two cephalopod species: the squid Loligo vulgaris and the cuttlefish Sepia officinalis. This is the first report of the immunohistochemical localization of cephalopod Na+/K+-ATPase with the polyclonal antibody α (H-300) raised against the human α1-subunit of Na+/K+-ATPase. Na+/K+-ATPase immunoreactivity was observed in several tissues (gills, pancreatic appendages, nerves), exclusively located in baso-lateral
membranes lining blood sinuses. Furthermore, large single cells in the gill of adult L. vulgaris specimens closely resembled Na+/K+-ATPase-rich cells described in fish. Immunohistochemical observations indicated that the amount and distribution of Na+/K+-ATPase in late cuttlefish embryos was similar to that found in juvenile and adult stages. The ion-regulatory epithelia (e.g.,
gills, excretory organs) of the squid embryos and paralarvae exhibited less differentiation than adults. Na+/K+-ATPase activities for whole animals were higher in hatchlings of S. officinalis (157.0 ± 32.4 μmol gFM−1 h−1) than in those of L. vulgaris (31.8 ± 3.3 μmol gFM−1 h−1). S. officinalis gills and pancreatic appendages achieved activities of 94.8 ± 18.5 and 421.8 ± 102.3 μmolATP gFM−1 h−1, respectively. High concentrations of Na+/K+-ATPase in late cephalopod embryos might be important in coping with the challenging abiotic conditions (low pH, high pCO2) that these organisms encounter inside their eggs. Our results also suggest a higher sensitivity of squid vs. cuttlefish
embryos to environmental acid-base disturbances. 相似文献
6.
Podophyllotoxin (PPT) and its derivatives exert significant anti-cancer activities, and one derivative etoposide is often
utilized to treat various cancers in the clinic. The aim of the present study is to investigate the inhibitory effects of
PPT on major cytochrome P450 (CYP) isoforms in human livers. Inhibition of CYP3A4, CYP2C9, CYP2C8, CYP2D6, CYP2E1 and CYP2A6
by PPT was investigated in the human liver microsomal system. Time-dependent inhibition of CYP3A4 by PPT was also evaluated.
The results showed that PPT strongly exhibited inhibitory effects on CYP3A4 and CYP2C9 in a concentration-dependent manner.
Half inhibition concentration (IC50) was 1.1 ± 0.3 and 4.6 ± 0.3 μM for CYP3A4 and CYP2C9, respectively. Inhibition kinetic analysis showed that PPT exhibited
competitive inhibition towards CYP3A4 and CYP2C9 with Ki of 1.6 and 2.0 μM, respectively. Additionally, PPT exerted time-dependent inhibition towards CYP3A4 and the kinetic parameters
were 4.4 ± 2.1 μM and 0.06 ± 0.01 min–1 for KI and kinact, respectively. Our experimental data indicate that potential drug–drug interaction (DDI) might exist when PPT is co-administered
with the substrates which mainly undergo CYP3A4- or CYP2C9-mediated metabolism. 相似文献
7.
We studied in batch reactors the kinetics and characterization of 70 °C, volatile fatty acids (VFAs)-grown, upflow anaerobic
sludge blanket granular sludge with 55 and 35 °C sludge as reference. The half-saturation constant (K
s), the inhibition constant (K
i), the maximum specific methane production rate (μCH4max), and the inhibition response coefficient (n) of the 70 °C sludge were 6.15 mM, 48.2 mM, 0.132 h−1, and 2.48, respectively, while no inhibition occurred at 55 and 35 °C, where the K
s was 3.67 and 3.82 mM, respectively. At 70 °C, the highest initial specific methanogenic activity (ISMA, 0.311 gCH4-COD per gram volatile solids per day) on VFAs was about 12–15% lower than that on acetate and three to four times less than
the ISMA for the 55 and 35 °C sludge. In the acetate conversion study, residual acetate (79 mg l−1) at 70 °C was three to five times higher than that at 55 and 35 °C. Further, the methane produced as percentage of the acetate
consumed at 70 °C (89%) was lower than that at 55 (95%) and 35 °C (97%). At 70 °C, 10% of the ISMA remained after 15 days
of starvation as compared to 26% (55 °C) and 92% (35 °C) after 30 days of starvation. Thus, the kinetics of the 70 °C granular
sludge seem to differ from those at 55 and 35 °C.
Received: 1 February 1999 / Accepted: 20 March 1999 相似文献
8.
The present research work was aimed to formulate clotrimazole encapsulated Cavamax W7 composite ethosomes by injection method
for improved delivery across epidermis. 32 factorial design was used to design nine formulations (F1-F9) and compared with ethosomal formulations (F10-F12). F9 with
vesicle size of 202.8 ± 4.8 nm, highest zeta potential (−83.6 ± 0.96 mV) and %EE of 98.42 ± 0.15 was selected as optimized
composite ethosome and F12 as reference ethosomal formulation. As revealed by transmission electron microscopy F9 vesicles
were more condensed, uniformly spherical in shape than F12 vesicles. Vesicular stability studies indicated F9 to be more stable
as compared to F12. Both F9 and F12 were incorporated in carbopol 934 gel base to get G1–G8 gel formulations and evaluated
for in vitro skin permeability. Cavamax W7 composite ethosomal optimized gel (G5) showed higher in vitro percent cumulative drug permeation (88.53 ± 2.10%) in 8 h and steady state flux (J
ss) of 3.39 ± 1.45 μg/cm2/min against the J
ss of 1.57 ± 0.23 μg/cm2/min for ethosomal gel (G1) and 1.13 ± 0.06 μg/cm2/min for marketed formulation. The J
ss flux of G5 was independent of amount of drug applied/unit area of skin. In vivo confocal laser scanning microscopic study of G5 depicted uniform and deeper penetration of rhodamine B (marker) in epidermis
from Cavamax W7 composite ethosomal gel in comparison to G1. Finally, G5 demonstrated better (p < 0.05) antifungal activity against Candida albicans and Aspergillus niger than G1 thus, signifying that Cavamax W7 composite ethosomes present a superior stable and efficacious vesicular system than
ethosomal formulation for topical delivery of clotrimazole. 相似文献
9.
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
10.
Nicola D’Amelio Luca Fontanive Fulvio Uggeri Furio Suggi-Liverani Luciano Navarini 《Food biophysics》2009,4(4):321-330
Caffeine complexation by chlorogenic acid (3-caffeoylquinic acid, CAS Number [327-97-9]) in aqueous solution as well as caffeine–chlorogenate
complex in freshly prepared coffee brews have been investigated by high-resolution 1H-NMR. Caffeine and chlorogenic acid self-associations have also been studied and self-association constants have been determined
resorting to both classical isodesmic model and a recently introduced method of data analysis able to provide also the critical
aggregation concentration (cac). Furthermore, caffeine–chlorogenate association constant was measured. For the caffeine, the
average value of the self-association constant determined by isodesmic model (K
i = 7.6 ± 0.5 M−1) is in good agreement with the average value (K
a = 10 ± 1.8 M−1) determined with the method which permits the determination of the cac (8.43 ± 0.05 mM). Chlorogenic acid shows a slight
decreased tendency to aggregation with a lower average value of association constants (K
i = 2.8 ± 0.6 M−1; K
a = 3.4 ± 0.6 M−1) and a critical concentration equal to 24 ± 1 mM. The value of the association constant of the caffeine–chlorogenate complex
(30 ± 4 M−1) is compatible with previous studies and within the typical range of reported association constants for other caffeine–polyphenol
complexes. Structural features of the complex have also been investigated, and the complex conformation has been rediscussed.
Caffeine chemical shifts comparison (monomeric, complexed, coffee brews) clearly indicates a significant amount of caffeine
is complexed in beverage real system, being chlorogenate ions the main complexing agents. 相似文献
11.
The membrane-bound F1 sector of the H+–ATPase complex (F-type ATPase) in dark-adapted photosynthetic chromatophores is endowed with MgATP- and CaATP-dependent ATPase
activities, both sensitive to inhibitors such as oligomycin and venturicidin. Because of contatamination of free Mg2
+ and Ca2+ ions in chromatophore preparations, kinetic characterization of the two hydrolitic reactions can be performed only in the
presence of both substrates, using a model for two alternative substrates. The two activities are characterized by similar
maximal rates and affinity constants [VMgATP and VCaATP: 13±1 and 10±1 nmol s–1 ATP hydrolyzed (μmol BChl)–1; KMgATP and KCaATP: 0.22±0.06 and 0.20±0.05 mm]. However, only the MgATP-dependent ATPase is coupled to Δ*H
+ generation. In this process CaATP acts as an alternative substrate and a competitive inhibitor of the proton pump, with a
KI coincident with KCaATP for the hydrolytic activity. This finding highlights the central role that the coordination chemistry of the ion-nucleotide
complex plays in determining the proton gating mechanism at the catalytic site(s) of the enzyme complex. These results are
discussed on the basis of the coordination properties of the ions and of the available information on the protein structure.
Received: 5 December 1995 / Accepted: 7 March 1996 相似文献
12.
Ingrid Sumeri Liisa Arike Jelena Stekolštšikova Riin Uusna Signe Adamberg Kaarel Adamberg Toomas Paalme 《Applied microbiology and biotechnology》2010,86(6):1925-1931
The effect of stress pretreatment on survival of probiotic Lactobacillus acidophilus La-5, Lactobacillus rhamnosus GG, and Lactobacillus fermentum ME-3 cultures was investigated in the single bioreactor gastrointestinal tract simulator (GITS). The cultures were pregrown
in pH-auxostat, subjected to temperature, acid, or bile stress treatment, fast frozen in liquid nitrogen (LN2), and tested for survival in GITS. After LN2 freezing the colony forming ability of L. rhamnosus GG and L. fermentum ME-3 nonstressed and stressed cells was well retained (average survival of 75.4 ± 18.3% and 88.0 ± 7.2%, respectively). L. acidophilus La-5 strain showed good survival of auxostat nonstressed cells after fast freezing (94.2 ± 15.0), however the survival of
stress pretreated cells was considerably lower (30.8 ± 8.5%). All LN2 frozen auxostat cultures survived well in the acid phase of the GIT simulation (survival 81 ± 21%); however, after the bile
phase, the colony formation ability of L. acidophilus La-5, L. rhamnosus GG, and L. fermentum ME-3 decreased by approximately 1.4 ± 0.2, 3.8 ± 0.3, and 3.5 ± 1.2 logarithmic units, respectively. No statistically relevant
positive effect of stress pretreatments on survival of LN2 frozen L. acidophilus La-5, L. rhamnosus GG, and L. fermentum ME-3 in GITS was observed. 相似文献
13.
Herbert R. L. Drouin 《European biophysics journal : EBJ》1999,28(7):600-604
A new ion-selective liquid membrane microelectrode, based on the neutral carrier 1,1′-bis(2,3-naphtho-18-crown-6), is described
that shows the dependence of EMF on the activity of divalent putrescine cations a
Put, with the linear slope s
Put = 26 ± 3 mV/decade (mean ± SD, N = 18), in the range 10−4–10−1 M at 25 ± 1 °C. Values of potentiometric putrescine cation selectivity coefficients of logK
Pot
Put
j
(mean ± SD, N) are obtained by the separate solution method for the ions K+ (1.0 ± 0.4, 10), Na+ (−1.2 ± 0.4, 8), Ca2+ (−2.3 ± 0.5, 10) and Mg2+ (−2.5 ± 0.5, 7). The microelectrode can be applied for the direct analysis of the activities of free divalent putrescine
cations in the range 5 × 10−4 to 10−1 M in an extracellular ionic environment. Established analytical methods, e.g. high performance liquid chromatography, determine
the total concentration of the derivatives of free and bound putrescine.
Received: 20 December 1998 / Revised version: 7 May 1999 / Accepted: 27 May 1999 相似文献
14.
Nucleoside di- and triphosphates and adenosine regulate several components of the mucocilairy clearance process (MCC) that
protects the lung against infections, via activation of epithelial purinergic receptors. However, assessing the contribution
of individual nucleotides to MCC functions remains difficult due to the complexity of the mechanisms of nucleotide release
and metabolism. Enzymatic activities involved in the metabolism of extracellular nucleotides include ecto-ATPases and secreted
nucleoside diphosphokinase (NDPK) and adenyl kinase, but potent and selective inhibitors of these activities are sparse. In
the present study, we discovered that ebselen markedly reduced NDPK activity while having negligible effect on ecto-ATPase
and adenyl kinase activities. Addition of radiotracer [γ
32P]ATP to human bronchial epithelial (HBE) cells resulted in rapid and robust accumulation of [32P]-inorganic phosphate (32Pi). Inclusion of UDP in the incubation medium resulted in conversion of [γ
32P]ATP to [32P]UTP, while inclusion of AMP resulted in conversion of [γ
32P]ATP to [32P]ADP. Ebselen markedly reduced [32P]UTP formation but displayed negligible effect on 32Pi or [32P]ADP accumulations. Incubation of HBE cells with unlabeled UTP and ADP resulted in robust ebselen-sensitive formation of
ATP (IC50 = 6.9 ± 2 μM). This NDPK activity was largely recovered in HBE cell secretions and supernatants from lung epithelial A549
cells. Kinetic analysis of NDPK activity indicated that ebselen reduced the V
max of the reaction (K
i = 7.6 ± 3 μM), having negligible effect on K
M values. Our study demonstrates that ebselen is a potent non-competitive inhibitor of extracellular NDPK. 相似文献
15.
The influence of low temperature (5–29 °C) on the methanogenic activity of non-adapted digested sewage sludge and on temperature/leachate-adapted
biomass was assayed by using municipal landfill leachate, intermediates of anaerobic degradation (propionate) and methane
precursors (acetate, H2/CO2) as substrates. The temperature dependence of methanogenic activity could be described by Arrhenius-derived models. However,
both substrate and adaptation affected the temperature dependence. The adaptation of biomass in a leachate-fed upflow anaerobic
sludge-blanket reactor at approximately 20 °C for 4 months resulted in a sevenfold and fivefold increase of methanogenic activity
at 11 °C and 22 °C respectively. Both acetate and H2/CO2 were methanized even at 5 °C. At 22 °C, methanogenic activities (acetate 4.8–84 mM) were 1.6–5.2 times higher than those
at 11 °C. The half-velocity constant (K
s) of acetate utilization at 11 °C was one-third of that at 22 °C while a similar K
i was obtained at both temperatures. With propionate (1.1–5.5 mM) as substrate, meth‐anogenic activities at 11 °C were half
those at 22 °C. Furthermore, the residual concentration of the substrates was not dependent on temperature. The results suggest
that the adaptation of biomass enables the achievement of a high treatment capacity in the anaerobic process even under psychrophilic
conditions.
Received: 23 December 1996 / Received last revision: 18 June 1997 / Accepted: 23 June 1997 相似文献
16.
An DS Cui CH Sung BH Yang HC Kim SC Lee ST Im WT Kim SG 《Applied microbiology and biotechnology》2012,94(3):673-682
The gene encoding an α-l-arabinofuranosidase that could biotransform ginsenoside Rc {3-O-[β-d-glucopyranosyl-(1–2)-β-d-glucopyranosyl]-20-O-[α-l-arabinofuranosyl-(1–6)-β-d-glucopyranosyl]-20(S)-protopanaxadiol} to ginsenoside Rd {3-O-[β-d-glucopyranosyl-(1–2)-β-d-glucopyranosyl]-20-O-β-d-glucopyranosyl-20(S)-protopanaxadiol} was cloned from a soil bacterium, Rhodanobacter ginsenosidimutans strain Gsoil 3054T, and the recombinant enzyme was characterized. The enzyme (AbfA) hydrolyzed the arabinofuranosyl moiety from ginsenoside
Rc and was classified as a family 51 glycoside hydrolase based on amino acid sequence analysis. Recombinant AbfA expressed
in Escherichia coli hydrolyzed non-reducing arabinofuranoside moieties with apparent K
m values of 0.53 ± 0.07 and 0.30 ± 0.07 mM and V
max values of 27.1 ± 1.7 and 49.6 ± 4.1 μmol min−1 mg−1 of protein for p-nitrophenyl-α-l-arabinofuranoside and ginsenoside Rc, respectively. The enzyme exhibited preferential substrate specificity of the exo-type
mode of action towards polyarabinosides or oligoarabinosides. AbfA demonstrated substrate-specific activity for the bioconversion
of ginsenosides, as it hydrolyzed only arabinofuranoside moieties from ginsenoside Rc and its derivatives, and not other sugar
groups. These results are the first report of a glycoside hydrolase family 51 α-l-arabinofuranosidase that can transform ginsenoside Rc to Rd. 相似文献
17.
Continuous production of lactic acid from lactose has been carried out in a stirred-tank reactor with non-growing Lactobacillus helveticus entrapped in calcium alginate beads. A considerably longer operation half-life was obtained in a continuously operated reactor
than in a batch-operated reactor. It is possible to simulate the action of entrapped non-growing cells on the basis of information
from diffusion and kinetic experiments with suspended free cells. The simulation fit the experimental data over a broad range
of substrate concentrations if the specific lactic acid production rate, q
P, was used as a variable parameter in the model. The dynamic mathematical model used is divided into three parts: the reactor
model, which describes the mass balance in a continuously operated stirred-tank reactor with immobilized biomass, the mass-transfer
model including both external diffusion and internal mass transfer, and the kinetic model for uptake of substrate on the basis
of a Michaelis-Menten-type mechanism. From kinetic data obtained for free biomass experiments it was found, with the use of
non-linear parameter estimation techniques, that the conversion rate of lactose by L. helveticus followed a Michaelis-Menten-type mechanism with K
S at half-saturation=0.22±0.01 g/l. The maximum specific lactose uptake rate for growing cells, q
S,max, varied between 4.32±0.02 g lactose g cells-1 h-1 and 4.89 ±0.02 g lactose g cells-1 h-1. The initial specific lactose uptake rate for non-growing cells, q
S,0, was found to be approximately 40% of the maximum specific lactose uptake rate for growing cells.
Received: 4 October 1995/Received last revision: 23 April 1996/Accepted: 29 April 1996 相似文献
18.
M Chellapandian C Larios M Sanchez-Gonzalez A Lopez-Munguia 《Journal of industrial microbiology & biotechnology》1998,21(1-2):51-56
Dextransucrase was produced from a Leuconostoc mesenteroides isolated from pulque, a traditional Aztec alcoholic beverage produced from agave juice containing sucrose as the main carbon source. Almost all
the dextransucrase activity (87%) was associated with the cells, and was unusually high (1.04 U mg−1 of cells). The culture medium composition was optimized through a Box-Behnken method resulting in a process yielding 2.2 U ml−1 of insoluble glucosyltransferase activity. The enzyme had a molecular weight of 166 kDa. Optimal temperature was 35°C with
a half-life of 137 min at the same temperature. As with dextransucrase from the industrial strain L. mesenteroides NRRL B-512F, the enzyme showed Michaelis–Menten kinetic behavior with excess substrate inhibition (K
m and K
i values of 0.026 M and 1.23 M respectively); produced soluble linear dextran with glucose molecules linked mainly in α(1–6)
with branching in α(1–3) in a proportion of 4:1 as shown by NMR studies; and produced a high yield of isomalto-oligosaccharides
in the presence of maltose.
Received 4 February 1998/ Accepted in revised form 25 July 1998 相似文献
19.
Wang LW Xu BG Wang JY Su ZZ Lin FC Zhang CL Kubicek CP 《Applied microbiology and biotechnology》2012,93(3):1231-1239
Through bioassay-guided fractionation, the EtOAc extract of a culture broth of the endophytic fungus Phoma species ZJWCF006 in Arisaema erubescens afforded a new α-tetralone derivative, (3S)-3,6,7-trihydroxy-α-tetralone (1), together with cercosporamide (2), β-sitosterol (3), and trichodermin (4). The structures of compounds were established on the basis of spectroscopic analyses. Compounds 1, 2, and 3 were obtained from Phoma species for the first time. Additionally, the compounds were subjected to bioactivity assays, including antimicrobial activity,
against four plant pathogenic fungi (Fusarium oxysporium, Rhizoctonia solani, Colletotrichum gloeosporioides, and Magnaporthe oryzae) and two plant pathogenic bacteria (Xanthomonas campestris and Xanthomonas oryzae), as well as in vitro antitumor activities against HT-29, SMMC-772, MCF-7, HL-60, MGC80-3, and P388 cell lines. Compound
1 showed growth inhibition against F. oxysporium and R. solani with EC50 values of 413.22 and 48.5 μg/mL, respectively. Additionally, compound 1 showed no cytotoxicity, whereas compound 2 exhibited cytotoxic activity against the six tumor cell lines tested, with IC50 values of 9.3 ± 2.8, 27.87 ± 1.78, 48.79 ± 2.56, 37.57 ± 1.65, 27.83 ± 0.48, and 30.37 ± 0.28 μM, respectively. We conclude
that endophytic Phoma are promising sources of natural bioactive and novel metabolites. 相似文献
20.
M. V. Potapovich V. P. Kurchenko D. I. Metelitza O. I. Shadyro 《Applied Biochemistry and Microbiology》2011,47(4):346-355
Inhibition efficiency (antioxidant activity) of 26 oxygen-containing aromatic compounds was studied in methemalbumin-H2O2-o-phenylenediamine (PDA) or tetramethylbenzidine (TMB) pseudoperoxidase system at 20°C in buffered physiological solution (pH
7.4) containing 6% DMF and 0.25% DMSO. The inhibitor’s efficiency was quantitatively characterized by the inhibition constants
(K
i, μM) or the inhibition degree (%). K
i values varied in the range of 4 to 500 μM and were influenced by a substrate, the structure of an inhibitor, hydroxyl groups,
electron-donating substituents in aromatic ring, and steric hindrances. The type of inhibition at cooxidation of eight pairs
was noncompetitive, and that of five pairs was mixed and determined by the substrate nature and the inhibitor structure. Lignin
phenolic compounds of guaiacyl and syringal series exhibited high antioxidant activity (K
i in the range of 10–300 μM), and their efficiency decreased in the following order: caffeic acid > synapaldehyde > syringic
acid > coniferyl aldehyde > para-hydroxycoumaric acid. 相似文献