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1.
Jennings BL Bell JD Hyodo S Toop T Donald JA 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2007,177(5):557-567
This study investigated vasodilator mechanisms in the dorsal aorta of the elephant fish, Callorhinchus milii, using anatomical and physiological approaches. Nitric oxide synthase could only be located in the perivascular nerve fibres
and not the endothelium of the dorsal aorta, using NADPH histochemistry and immunohistochemistry. In vitro organ bath experiments
demonstrated that a NO/soluble guanylyl cyclase (GC) system appeared to be absent in the vascular smooth muscle, since the
NO donors SNP (10−4 mol l−1) and SIN-1 (10−5 mol l−1) were without effect. Nicotine (3 × 10−4 mol l−1) mediated a vasodilation that was not affected by ODQ (10−5 mol l−1), l-NNA (10−4 mol l−1), indomethacin (10−5 mol l−1), or removal of the endothelium. In contrast, the voltage-gated sodium channel inhibitor, tetrodotoxin (10−5 mol l−1), significantly decreased the dilation induced by nicotine, suggesting that it contained a neural component. Pre-incubation
of the dorsal aorta with the calcitonin gene-related peptide (CGRP) receptor antagonist, CGRP8–37 (10−6 mol l−1) also caused a significant decrease in the nicotine-induced dilation. We propose that nicotine is mediating a neurally-derived
vasodilation in the dorsal aorta that is independent of NO, prostaglandins and the endothelium, and partly mediated by CGRP. 相似文献
2.
An effective, simple, and convenient method to improve yeast’s multiple-stress tolerance, and ethanol production was developed.
After an ethanologenic Saccharomyces cerevisiae strain SC521 was treated by nine cycles of freeze-thaw, a mutant FT9-11 strain with higher multiple-stress tolerance was
isolated, whose viabilities under acetic acid, ethanol, freeze-thaw, H2O2, and heat-shock stresses were, respectively, 23-, 26-, 10- and 7-fold more than the parent strain at an initial value 2 × 107 c.f.u. per ml. Ethanol production of FT9-11 was similar (91.5 g ethanol l−1) to SC521 at 30°C with 200 g glucose l−1, and was better than the parent strain at 37°C (72.5 g ethanol l−1), with 300 (111 g ethanol l−1) or with 400 (85 g ethanol l−1) g glucose l−1. 相似文献
3.
H. J. Carlisle T. G. Hales B. A. Schlinger 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1998,182(4):531-538
Songbirds are widely studied to investigate the hormonal control of behavior. However, little is known about the effects
of steroids on neurotransmission in these birds. We used electrophysiological and pharmacological techniques to characterize
γ-aminobutyric acid (GABA) type A receptors (GABAA) of primary cultured telencephalic and hippocampal neurons from developing zebra finches. Additionally, their modulation
by 17β-estradiol(E2), 5α- and 5β-dihydrotestosterone (DHT), 5α- and 5β-pregnan-3α-ol-20-one, and corticosterone was examined. Whole-cell GABA-evoked
currents were inhibited by picrotoxin (10 μmol l−1) and bicuculline methiodide (10 μmol l−1) and potentiated by pentobarbital (100 μmol l−1) and propofol (3 μmol l−1). Loreclezole (10 μmol l−1) potentiated GABA-evoked currents, suggesting the presence of β2, β3 and/or β4 subunits. Diazepam (1 μmol l−1) potentiated currents, while Zn2+ (1 μmol l−1) caused no inhibition, indicating the presence of γ subunits. 5α- and 5β-Pregnan-3α-ol-20-one (100 nmol l−1) potentiated currents, whereas E2 (1 μmol l−1), 5α- and 5β-DHT (1 μmol l−1), and corticosterone (10 μmol l−1) had no detectable effect. We conclude that zebra finch telencephalic and hippocampal GABAA receptors include α, β, and γ subunits and are similar to their mammalian counterparts in both their biophysical and pharmacological
properties. Additionally, GABA-evoked currents are greatly potentiated by 5α- and 5β-pregnan-3α-ol-20-one but show little
or no acute modulation by sex steroids or corticosterone.
Accepted: 12 November 1997 相似文献
4.
Plant regeneration from callus culture of a Paphiopedilum hybrid 总被引:4,自引:0,他引:4
Totipotent calli of a Paphiopedilum hybrid (Paphiopedilum callosum ‘Oakhi’ × Paph. lawrenceanum ‘Tradition’) were induced from seed-derived protocorms on a 1/2 strength Murashige–Skoog medium plus 1–10 mg l−1 2,4-dichlorophenoxyacetic acid (2,4-D) and 0.1–1 mg l−1 1-phenyl-3-(1.2.3-thiadiazol-5-yl)urea (TDZ). These calli grew well when subcultured on the same medium, but proliferated
more on 1/2 MS medium plus 5 mg l−1 2,4-D and 1 mg l−1 TDZ. Calli developed further along a route of production of protocorm-like bodies and eventually formed plantlets that could
be transplanted to pots and grew well.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
5.
We evaluated the combined effects of algal (Chlorella vulgaris) food levels (low, 0.5 × 106 (or 2.9 μg C ml−1); and high, 1 × 106 cells ml−1 (or 5.8 μg C ml−1)) and zinc concentrations (0, 0.125, and 0.250 mg l−1 of ZnCl2) on the competition between two common planktonic rotifers Anuraeopsis fissa and Brachionus rubens using their population growth. Median lethal concentration data (LC50) (mean ± 95% confidence intervals) showed that B. rubens was more resistant to zinc (0.554 ± 0.08 mg l−1) than A. fissa (0.315 ± 0.07 mg l−1). A. fissa when grown alone or with Zn was always numerically more abundant than B. rubens. When grown in the absence of zinc, under low- and high-food levels, the peak abundances of A. fissa varied from 251 ± 24 to 661 ± 77 ind. ml−1, respectively, and the corresponding maxima for B. rubens were 52 ± 3 and 102 ± 18 ind. ml−1. At a given food level, competition for food reduced the peak abundances of both rotifers considerably. Increase in Zn concentration
also lowered the rotifer abundances. The impact of zinc on competition between the two-rotifer species was evident at low-food
level, mainly for A. fissa. At zinc concentrations of 0 and 0.125 mg l−1, the populations of both rotifers continued to grow for about 10 days, but thereafter B. rubens began to decline. Role of zinc on the competitive outcome of the two species is discussed in relation to the changing algal
densities in natural water bodies. 相似文献
6.
Lakkana Laopaiboon Pornthap Thanonkeo Prasit Jaisil Pattana Laopaiboon 《World journal of microbiology & biotechnology》2007,23(10):1497-1501
Sweet sorghum juice supplemented with 0.5% ammonium sulphate was used as a substrate for ethanol production by Saccharomyces cerevisiae TISTR 5048. In batch fermentation, kinetic parameters for ethanol production depended on initial cell and sugar concentrations.
The optimum initial cell and sugar concentrations in the batch fermentation were 1 × 108 cells ml−1 and 24 °Bx respectively. At these conditions, ethanol concentration produced (P), yield (Y
ps) and productivity (Q
p
) were 100 g l−1, 0.42 g g−1 and 1.67 g l−1 h−1 respectively. In fed-batch fermentation, the optimum substrate feeding strategy for ethanol production at the initial sugar
concentration of 24 °Bx was one-time substrate feeding, where P, Y
ps and Q
p
were 120 g l−1, 0.48 g g−1 and 1.11 g l−1 h−1 respectively. These findings suggest that fed-batch fermentation improves the efficiency of ethanol production in terms of
ethanol concentration and product yield. 相似文献
7.
To develop an integrated process of CO2-fixation and H2 photoproduction by marine green microalga Platymonas subcordiformis, the impact of algal cells grown in CO2-supplemented air bubble column bioreactor was investigated on H2 photoproduction regulated by carbonylcyanide m-chlorophenylhrazone. Highest cell growth (3.85 × 106 cells ml−1), starch content (0.25 ± 0.08 mg per 106 cells) and hydrogen production (50 ± 3 ml l−1) were achieved at 3% CO2-supplemented culture, which are respectively 1.4, 2.1, 1.5-fold of the air-supplemented culture. Improved H2 production correlated well with the increase in starch accumulation. In this process, the algal cells have been recycled
for stable H2 production of 40–50 ml l−1 over five cycles. 相似文献
8.
Extracellular human granulocyte-macrophage colony stimulating factor (hGM-CSF) expression was studied under the control of
the GAP promoter in recombinant Pichia pastoris in a series of continuous culture runs (dilution rates from 0.025 to 0.2 h−1). The inlet feed concentration was also varied and the steady state biomass concentration increased proportionally demonstrating
efficient substrate utilization and constancy of the biomass yield coefficient (Yx/s) for a given dilution rate. The specific product formation rate (qP) showed a strong correlation with dilution rates demonstrating growth associated product formation of hGM-CSF. The volumetric
product concentration achieved at the highest feed concentration (4×) and a dilution rate of 0.2 h−1 was 82 mg l−1 which was 5-fold higher compared to the continuous culture run with 1× feed concentration at the lowest dilution rate thus
translating to a 40 fold increase in the volumetric productivity. The specific product yield (YP/X) increased slightly from 2 to 2.5 mg g−1, with increasing dilution rates, while it remained fairly invariant, for all feed concentrations demonstrating negligible
product degradation or feed back inhibition. The robust nature of this expression system would make it easily amenable to
scale up for industrial production. 相似文献
9.
Characterization of the superoxide dismutase SOD1 gene of Kluyveromyces marxianus L3 and improved production of SOD activity 总被引:1,自引:0,他引:1
Raimondi S Uccelletti D Matteuzzi D Pagnoni UM Rossi M Palleschi C 《Applied microbiology and biotechnology》2008,77(6):1269-1277
Superoxide dismutase (SOD) activity is one major defense line against oxidative stress for all of the aerobic organisms, and
industrial production of this enzyme is highly demanded. The Cu/Zn superoxide dismutase gene (KmSOD1) of Kluyveromyces marxianus L3 was cloned and characterized. The deduced KmSod1p protein shares 86% and 71% of identity with Kluyveromyces lactis and Saccharomyces cerevisiae Sod1p, respectively. The characteristic motifs and the amino acid residues involved in coordinating copper and zinc and in
enzymatic function were conserved. To the aim of developing a microbial production of Cu/Zn superoxide dismutase, we engineered
the K. marxianus L3 strain with the multicopy plasmid YG-KmSOD1 harboring the KmSOD1 gene. The production of KmSOD1p in K. marxianus L3 and K. marxianus L3 (pYG-KmSOD1) in response to different compositions of the culture medium was evaluated. The highest specific activity
(472 USOD mgprot
−1) and the highest volumetric yield (8.8 × 105 USOD l−1) were obtained by the recombinant strain overexpressing KmSOD1 in the presence of Cu2+ and Zn2+ supplements to the culture media. The best performing culture conditions were positively applied to a laboratory scale fed-batch
process reaching a volumetric yield of 1.4 × 106 USOD l−1.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
10.
Fabiana R. X. Batista Carlos A. Pereira Ronaldo Z. Mendon?a Angela M. Moraes 《Cytotechnology》2005,49(1):1-9
Animal cells can be cultured both in basal media supplemented with fetal bovine serum (FBS) and in serum-free media. In this
work, the supplementation of Grace’s medium with a set of nutrients to reduce FBS requirements in Spodoptera frugiperda (Sf9) cell culture was evaluated, aiming the production of Anticarsia gemmatalis nucleopolyhedrovirus (AgMNPV) at a cost lower than those for the production using Sf900 II medium. In Grace’s medium supplemented
with glucose, Pluronic F68 (PF68) and yeast extract (YE), the effects of FBS and milk whey ultrafiltrate (MWU) on cell concentration
and viability during midexponential and stationary growth phase were evaluated. In spite of the fact that FBS presented higher
statistical effects than MWU on all dependent variables in the first cell passage studies, after cell adaptation, AgMNPV polyhedra
production was comparable to that in Sf900 II. Batch cultivation in Grace’s medium with 2.7 g l−1 glucose, 8 g l−1 YE and 0.1% (w/v) PF68 supplemented with 1% (w/v) MWU and 3% (v/v) FBS increased viable cell concentration to about 5-fold
(4.7×106 cells ml−1) when compared to Grace’s containing 10% (v/v) FBS (9.5×105 cells ml−1). AgMNPV polyhedra (PIBs) production was around 3-fold higher in the MWU supplemented medium (1.6×107 PIBs ml−1) than in Grace’s medium with 10% FBS (0.6×107 PIBs ml−1). This study therefore shows a promising achievement to significantly reduce FBS concentration in Sf9 insect cell media,
keeping high productivity in terms of cell concentration and final virus production at a cost almost 50% lower than that observed
for Sf900 II medium.
C.A. Pereira is recipient of a CNPq fellowship. 相似文献
11.
Zanaty R. Komy Rabei M. Gabar Ahmed A. Shoriet Rehab M. Mohammed 《World journal of microbiology & biotechnology》2006,22(9):975-982
Summary The ability of Pseudomonas
aeruginosa to accumulate Cd(II) ions from wastewater industries was experimentally investigated and mathematically modelled. From the potentiometric titration and non-ideal competitive analysis (NICA) model, it was found that the biomass contains three acidic sites. The values of proton binding (pK
i
=1.66±3.26×10−3, 1.92±1.63×10−4 and 2.16±3.79×10−4) and binding constant of cadmium metal ions (pK
M1=1.99±2.45×10−3 and pK
M2=1.67±4.08×10−3) on the whole surface of biomass showed that protonated functional groups and biosorption of Cd(II) ions could be attributed to a monodentate binding to one acidic site, mainly the carboxylic group. From the isothermal sorption experimental data and Langmuir model, it was also found that the value of Langmuir equilibrium (pK
f) constant is 2.04±2.1×10−5 suggesting that the carboxyl group is the main active binding site. In addition, results showed that the maximum cadmium capacity (q
max) and affinity of biomass towards cadmium metal ions (b) at pH 5.1 and 20 min were 96.5±0.06 mg/g and 3.40×10−3± 2.10×10−3, respectively. Finally, interfering metal ions such as Pb(II), Cu(II), Cr(III), Zn(II), Fe(II), Mn(II), Ca(II) and Mg(II) inhibited Cd(II) uptake. Comparing the biosorption of Cd(II) by various Pseudomonas isolates from contaminated environment samples (soil and sewage treatment plant) showed that maximum capacities and equilibrium times were different, indicating that there was a discrepancy in the chemical composition between biomasses of different strains. 相似文献
12.
Luiz Eduardo Maia Nery Marcelo Alves da Silva Lars Josefsson Ana Maria Lauro Castrucci 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(8):570-575
The cellular system responsible for the transduction of the pigment-concentrating hormone (PCH) signal was investigated in
erythrophores of the freshwater shrimp, Macrobrachium potiuna. Dose-response curves to the hormone were determined in the absence and in the presence of several drugs that affect sequential
steps of the Ca2+-dependent signalling pathway. Additionally, the ability of forskolin to induce pigment dispersion was evaluated. Neomycin
sulphate (10−4 and 10−3 mol · l−1), trifluoperazine (10−5 and 10−4 mol · l−1), 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (10−7 and 10−5 mol · l−1) and okadaic acid (10−7 mol · l−1) significantly (P<0.05) decreased the responses to PCH. However, okadaic acid at low concentration (10−9 mol · l−1) and cyclosporin A (10−6 and 10−5 mol · l−1) did not significantly (P>0.05) affect PCH activity. Forskolin (10−4 mol · l−1) was able to half-maximally reverse the hormone-induced aggregation. Our results suggest that the pigment-concentrating hormone
induces pigment aggregation through a Ca2+-dependent pathway with a posteriori phosphatase activation, probably the serine/threonine phosphatase 1.
Accepted: 30 June 1997 相似文献
13.
Jasna Hrenovic Tomislav Ivankovic Lavoslav Sekovanic Mirela Rozic 《Central European Journal of Biology》2008,3(2):143-148
The antibacterial effect of cationic surfactants against the pure culture of phosphate (P)-accumulating bacterium Acinetobacter junii was investigated. The estimated EC50 values of the N-dodecylpyridinium chloride (DPC) for growth inhibition was 1.4±0.5 × 10−6 mol L−1 and for the inhibition of the P-uptake rates 7.3±2.6 × 10−5 mol L−1. The estimated EC50 values of the N-cetylpyridinium chloride (CPC) for growth inhibition was 4.9±1.3 × 10−7 mol L−1 and for the inhibition of the P-uptake rates 7.7±2.9 × 10−6 mol L−1. This suggests the importance of controlling the amounts of cationic surfactants in influent of the wastewater treatment
systems in order to avoid the possible failure of the biological P removal from wastewaters. 相似文献
14.
The harmful effects of surfactants to the environment are well known. We were interested in investigating their potential
toxicity in a pure culture of Acinetobacter junii, a phosphate (P)-accumulating bacterium. Results showed a high acute toxicity of sodium dodecyl sulfate (SDS) and hexadecyltrimethylammonium
bromide (HDTMA) against A. junii. The estimated EC50 values of the HDTMA for the inhibition of CFUs in the pure culture of A. junii was 3.27 ± 1.12 × 10−7 mol L−1 and for the inhibition of the P-uptake rates 2.47 ± 0.51 × 10−6 mol L−1. For SDS, estimated EC50 values for the inhibition of CFUs in the pure culture of A. junii was 5.00 ± 2.95 × 10−6 mol L−1 and for the inhibition of the P-uptake rates 3.33 ± 0.96 × 10−4 mol L−1. The obtained EC50 values in the standardised yeast toxicity test using Saccharomyces cerevisiae were 3.03 ± 0.38 × 10−4 and 4.33 ± 0.32 × 10−5 mol L−1 for SDS and HDTMA, respectively. These results emphasized the need to control concentrations of surfactants entering the
activated sludge system. The negative effects of these toxicants could greatly decrease populations of P-accumulating bacteria,
as well as eukaryotic organisms, inhabiting activated sludge systems, which in turn could result in the decrease of the system
efficiency. 相似文献
15.
We investigated the effects of limiting (1.96 × 10−9 mol l−1 total Cu, corresponding to pCu 14.8; where pCu = −log [Cu2+]) and toxic Cu concentrations up to 8.0 × 10−5 mol l−1 total Cu (equivalent to pCu 9.5) on growth rates and photosynthetic activity of exponentially grown Phaeocystis cordata, using batch and semi-continuous cultures. With pulse amplitude modulated (PAM) fluorometry, we determined the photochemical
response of P. cordata to the various Cu levels, and showed contrasting results for the batch and semi-continuous cultures. Although maximum photosystem
II (PSII) quantum yield (ΦM) was optimal and constant in the semi-continuous P. cordata, the batch cultures showed a significant decrease in ΦM with culture age (0–72 h). The EC50 for the batch cultures was higher (2.0 × 10−10 mol l−1, pCu9.7), than that for the semi-continuous cultures (6.3 × 10−11 mol l−1, pCu10.2). The semi-continuous cultures exhibited a systematic and linear decrease in ΦM as Cu levels increased (for [Cu2+] < 1.0 × 10−12 mol l−1, pCu12.0), however, no effect of high Cu was observed on their operational PSII quantum yield (Φ′M). Similarly, semi-continuous cultures exhibited a significant decrease in ΦM, but not in Φ′M, because of low-Cu levels. Thus, Cu toxicity and Cu limitation damage the PSII reaction centers, but not the processes downstream
of PSII. Quenching mechanisms (NPQ and Q
n) were lower under high Cu relative to the controls, suggesting that toxic Cu impairs photo-protective mechanisms. PAM fluorometry
is a sensitive tool for detecting minor physiological variations. However, culturing techniques (batch vs. semi-continuous)
and sampling time might account for literature discrepancies on the effects of Cu on PSII. Semi-continuous culturing might
be the most adequate technique to investigate Cu effects on PSII photochemistry. 相似文献
16.
Hwang HS Lee SH Baek YM Kim SW Jeong YK Yun JW 《Applied microbiology and biotechnology》2008,78(3):419-429
In the present study, optimum culture conditions for the production of extracellular polysaccharides (EPS) in submerged culture
of an edible mushroom, Laetiporus sulphureus var. miniatus and their stimulatory effects on insulinoma cell (RINm5F) proliferation and insulin secretion were investigated. The maximum
mycelial growth (4.1 g l−1) and EPS production (0.6 g l−1) in submerged flask culture were achieved in a medium containing 30 g l−1 maltose, 2 g l−1 soy peptone, and 2 mM MnSO4·5H2O at an initial pH 2.0 and temperature 25°C. In the stirred-tank fermenter under optimized medium, the concentrations of mycelial
biomass and EPS reached a maximum level of 8.1 and 3.9 g l−1, respectively. Interestingly, supplementation of deep sea water (DSW) into the culture medium significantly increased both
mycelial biomass and EPS production by 4- and 6.7-fold at 70% (v/v) DSW medium, respectively. The EPS were proved to be glucose-rich polysaccharides and were able to increase proliferation
and insulin secretary function of rat insulinoma RINm5F cells, in a dose-dependent manner. In addition, EPS also strikingly
reduced the streptozotocin-induced apoptosis in RINm5F cells indicating the mode of the cytoprotective role of EPS on RINm5F
cells. 相似文献
17.
We studied the response of Brachionus patulus to different concentrations of the heavy metal Pb in the presence and absence of sediments. We conducted acute (LC50) and chronic (life table demography and population growth) toxicity tests using sediment levels of 0, 30 and 280 mg l−1 (=0, 17 and 170 NTU) and Pb at 0, 0.06 and 0.6 mg l−1. Experiments were conducted at 20 ± 1°C on a horizontal shaker and algal food (Chlorella vulgaris) was added at a density of 1.0 × 106 cells ml−1. The median lethal concentration (LC50 ± 95% Confidence intervals) of PbCl2 for B. patulus was 6.15 ± 1.08 mg l−1. Age-specific survivorship and fecundity curves showed increase in turbidity level resulted in decreased survival and offspring
production of the rotifers. Increase in Pb concentration too had a negative effect on the survival and reproductive output
of B. patulus. Statistically, average lifespan, life expectancy at birth, gross and net reproductive rates and the rate of population increase
were all significantly influenced by the concentration of Pb, turbidity level as well as the interaction of Pb concentration × turbidity
level. Rotifers exposed to 170 NTU did not grow regardless of the heavy metal concentration in the medium. Similarly, B. patulus exposed to 0.6 mg l−1 Pb did not survive beyond 10 days regardless of the turbidity level in the medium. The rate of population increase of B. patulus derived from the growth experiments was negative in all treatments containing Pb as low as 0.06 mg l−1 or turbidity level as low as 17 NTU. In treatments containing Pb or sediments, there existed no relation between the egg
ratio and the population density.
Guest editors: S. S. S. Sarma, R. D. Gulati, R. L. Wallace, S. Nandini, H. J. Dumont and R. Rico-Martínez
Advances in Rotifer Research 相似文献
18.
A detailed survey was undertaken of the microbial communities of 16 saline lakes in the Vestfold Hills (Princess Elizabeth
Land, eastern Antarctica), which ranged in salinity from slightly brackish (4–5‰) to hypersaline (maximum: 174‰). Temperatures
at comparable sampling depths in the lakes ranged from −12.2°C to +10.5°C. Ranges in the abundances of bacteria, heterotrophic
nanoflagellates (HNAN) and phototrophic nanoflagellates (PNAN) were 1.40 × 107 l−1–1.58 × 1010 l−1, 4.83 × 104 l−1–1.70 × 107 l−1 and 0–1.02 × 107 l−1, respectively. There was considerable variation across the salinity spectrum, though in the case of bacteria and PNAN significantly
higher concentrations of cells were seen in two of the most saline lakes. The autotrophic ciliate Mesodinium rubrum occurred in all but five of the lakes and was found at salinity levels up to 108‰. Heterotrophic ciliates were generally
scarce. Dinoflagellates, particularly Gonyaulax c.f. tamarensis, Gyrodinium lachryma and Gymnodinium sp., occurred in the majority of the lakes. On the basis of chlorophyll a concentrations, nutrient levels and microplankton concentrations the lakes spanned the spectrum from ultra-oligotrophic to
oligo/mesotrophic. The most saline lakes had much reduced species diversity compared with the less saline environments. Isolation
from the marine environment has led to nutrient depletion, simplification and a truncated trophic structure.
Received: 19 September 1996 / Accepted: 13 January 1997 相似文献
19.
Theodoros Goulas Athanasios Goulas George Tzortzis Glenn R. Gibson 《Applied microbiology and biotechnology》2009,82(6):1079-1088
Four different β-galactosidases (previously named BbgI, BbgII, BbgIII and BbgIV) from Bifidobacterium bifidum NCIMB41171 were overexpressed in Escherichia coli, purified to homogeneity and their biochemical properties and substrate preferences comparatively analysed. BbgI was forming
a hexameric protein complex of 875 kDa, whereas BbgII, BbgIII and BbgIV were dimers with native molecular masses of 178, 351
and 248 kDa, respectively. BbgII was the only enzyme that preferred acidic conditions for optimal activity (pH 5.4–5.8), whereas
the other three exhibited optima in more neutral pH ranges (pH 6.4–6.8). Na+ and/or K+ ions were prerequisite for BbgI and BbgIV activity in Bis–Tris-buffered solutions, whereas Mg++ was strongly activating them in phosphate-buffered solutions. BbgII and BbgIII were slightly influenced from the presence
or absence of cations, with Mg++, Mn++ and Ca++ ions exerting the most positive effect. Determination of the specificity constants (k
cat/K
m) clearly indicated that BbgI (6.11 × 104 s−1 M−1), BbgIII (2.36 × 104 s−1 M−1) and especially BbgIV (4.01 × 105 s−1 M−1) are highly specialised in the hydrolysis of lactose, whereas BbgII is more specific for β-d-(1→6) galactobiose (5.59 × 104 s−1 M−1) than lactose (1.48 × 103 s−1 M−1). Activity measurements towards other substrates (e.g. β-d-(1→6) galactobiose, β-d-(1→4) galactobiose, β-d-(1→4) galactosyllactose, N-acetyllactosamine, etc.) indicated that the β-galactosidases were complementary to each other by hydrolysing different substrates and thus contributing in a different
way to the bacterial physiology. 相似文献
20.
Han Gil Choi Ki Hoon Lee Hyun Il Yoo Pil Jun Kang Young Sik Kim Ki Wan Nam 《Journal of applied phycology》2008,20(5):729-735
The effects of temperature, irradiance, and daylength on Sargassum horneri growth were examined at the germling and adult stages to discern their physiological differences. Temperature–irradiance
(10, 15, 20, 25, 30°C × 20, 40, 80 μmol photons m−2s−1) and daylength (8, 12, 16, 24 h) experiments were carried out. The germlings and blades of S. horneri grew over a wide range of temperatures (10–25°C), irradiances (20–80 μmol photons m−2s−1), and daylengths (8–24 h). At the optimal growth conditions, the relative growth rates (RGR) of the germlings were 21% day−1 (25°C, 20 μmol photons m−2s−1) and 13% day−1 (8 h daylength). In contrast, the RGRs of the blade weights were 4% day−1 (15°C, 20 μmol photons m−2s−1) and 5% day−1 (12 h daylength). Negative growth rates were found at 20 μmol photons m−2s−1 of 20°C and 25°C treatments after 12 days. This phenomenon coincides with the necrosis of S. horneri blades in field populations. In conclusion, we found physiological differences between S. horneri germlings and adults with respect to daylength and temperature optima. The growth of S. horneri germlings could be enhanced at 25°C, 20 μmol photons m−2s−1, and 8 h daylength for construction of Sargassum beds and restoration of barren areas. 相似文献