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1.
Luz Allende Guillermo Tell Horacio Zagarese Ana Torremorell Gonzalo Pérez José Bustingorry Roberto Escaray Irina Izaguirre 《Hydrobiologia》2009,624(1):45-60
Shallow lakes often alternate between two possible states: one clear with submerged macrophytes, and another one turbid, dominated
by phytoplankton. A third type of shallow lakes, the inorganic turbid, result from high contents of suspended inorganic material,
and is characterized by low phytoplankton biomass and macrophytes absence. In our survey, the structure and photosynthetic
properties (based on 14C method) of phytoplankton were related to environmental conditions in these three types of lakes in the Pampa Plain. The
underwater light climate was characterized. Clear-vegetated lakes were more transparent (K
d 4.5–7.7 m−1), had high DOC concentrations (>45 mg l−1), low phytoplankton Chl a (1.6–2.7 μg l−1) dominated by nanoflagellates. Phytoplankton productivity and photosynthetic efficiency (α ~ 0.03 mgC mgChla
−1 h−1 W−1 m2) were relatively low. Inorganic-turbid lakes showed highest K
d values (59.8–61.4 m−1), lowest phytoplankton densities (dominated by Bacillariophyta), and Chl a ranged from 14.6 to 18.3 μg l−1. Phytoplankton-turbid lakes showed, in general, high K
d (4.9–58.5 m−1) due to their high phytoplankton abundances. These lakes exhibited the highest Chl a values (14.2–125.7 μg l−1), and the highest productivities and efficiencies (maximum 0.56 mgC mgChla
−1 h−1 W−1 m2). Autotrophic picoplankton abundance, dominated by ficocianine-rich picocyanobacteria, differed among the shallow lakes independently
of their type (0.086 × 105–41.7 × 105 cells ml−1). This article provides a complete characterization of phytoplankton structure (all size fractions), and primary production
of the three types of lakes from the Pampa Plain, one of the richest areas in shallow lakes from South America.
Handling editor: J. Padisak 相似文献
2.
Chlorogenic acid, 3’-O-caffeoyl D-quinic acid, is an inherent ligand present inHelianthus annuus L. The effect of pH on chlorogenic acid binding to helianthinin suggests that maximum binding occurs at pH 6.0. The protein-polyphenol
complex precipitates as a function of time. The association constant of the binding of chlorogenic acid to helianthinin, determined
by equilibrium dialysis, at 31°C has a value of 3.5 ± 0.1 × 104M−-1 resulting in a ΔG value of − 6.32 ± 0.12 kcal /mol. The association constantK
ais 1.0 ± 0.1 × 104M−1 as determined by ultraviolet difference spectral titration at 25°C with ΔG° of -5.46 ± 0.06 kcal/mol. From fluorescence spectral
titration at 28°C, theK
avalue is 1.38 ± 0.1 × 1 0 4M−1 resulting in a ΔG of − 5.70 ± 0.05 kcal/mol. The total number of binding sites on the protein are 420 ± 50 as calculated
from equilibrium dialysis. Microcalorimetric data of the ligand-protein interaction at 23°C suggests mainly two classes of
binding. The thermal denaturation temperature,T
mof the protein decreases from 76°C to 72°C at 1 × 10−3M chlorogenic acid concentration upon complexation. This suggests that the complexation destabilizes the protein. The effect
of temperature onK
aof chlorogenic acid shows a nonlinear increase from 10.2°C to 45°C. Chemical modification of both lysyl and tryptophanyl residues
of the protein decreases the strength of binding of chlorogenic acid. Lysine, tryptophan and tyrosine of protein are shown
to be present at the binding site. Based on the above data, it is suggested that charge-transfer complexation and entropically
driven hydrophobic interaction are the predominant forces that are responsible for binding of chlorogenic acid to the multisubunit
protein, helianthinin.
Publication No. 324. 相似文献
3.
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
4.
Kim HT Ko HJ Kim N Kim D Lee D Choi IG Woo HC Kim MD Kim KH 《Biotechnology letters》2012,34(6):1087-1092
A gene, alg7D, from Saccharophagus degradans, coding for a putative alginate lyase belonging to the family of polysaccharide lyase-7, was overexpressed in Escherichia coli. The properties of the recombinant Alg7D were characterized. The enzyme endolytically depolymerized alginate by β-elimination
into oligo-alginates with degrees of polymerization of 2–5. Its activity was maximal at 50°C and pH 7 and was slightly increased
in the presence of Na+. The K
M
, V
max
, k
cat
, and k
cat
/K
M
values were: 3 mg ml−1, 6.2 U mg−1, 1.9 × 10−2 s−1, and 6.3 × 10−3 mg−1 ml s−1, respectively. 相似文献
5.
Fatah Chérifi Jean-Claude Rousselle Abdelkader Namane Fatima Laraba-Djebari 《The protein journal》2010,29(7):466-474
A procoagulant metalloproteinase called CCSV-MPase was purified from C. cerastes venom by successive chromatographic methods starting with gel-filtration through Sephadex G-75; ion-exchange DEAE-Cellulose
A-50; affinity chromatography on Benzamidine Sepharose 6B and RP-HPLC on a C8 column. CCSV-MPase has been isolated to an extent
of about tenfolds and its molecular mass was evaluated at 70 kDa by SDS–PAGE. CCSV-MPase hydrolyzes casein and fibrinogene
as natural substrates. Its proteolytic activity was inhibited by EDTA and 1.10-phenanthroline, a chelators of bivalent cation
metals and Zn2+ respectively. CCSV-MPase is therefore a Zn2+-metalloproteinase with fibrinogenolytic but not hemorrhagic activity. It greatly decreased levels of plasmatic fibrinogen
when administered to rats for 24 h. This fibrinogenase hydrolyzes the Bβ chain of human fibrinogen in vitro releasing fibrinopeptide
B only. LC MS/MS analysis of tryptic fragments of CCSV-MPase demonstrated that it showed some sequence similarities with four
other venom metalloproteinases. CCSV-MPase could be considered as a potential therapeutic agent as it is a non-hemorrhagic
enzyme and could be useful in thrombotic diseases because of its defibrinogenation of blood. 相似文献
6.
The effect of agitation and aeration on the growth and antibiotic production by Xenorhabdus nematophila YL001 grown in batch cultures were investigated. Efficiency of aeration and agitation was evaluated through the oxygen mass
transfer coefficient (K
L
a). With increase in K
L
a, the biomass and antibiotic activity increased. Activity units of antibiotic and dry cell weight were increased to 232 U ml−1 and 19.58 g l−1, respectively, productivity in cell and antibiotic was up more than 30% when K
L
a increased from 115.9 h−1 to 185.7 h−1. During the exponential growth phase, DO concentration was zero, the oxygen supply was not sufficient. So, based on process
analysis, a three-stage oxygen supply control strategy was used to improved the DO concentration above 30% by controlling
the agitation speed and aeration rate. The dry cell weight and activity units of antibiotic were further increased to 24.22 g l−1 and 249 U ml−1, and were improved by 24.0% and 7.0%, compared with fermentation at a constant agitation speed and a constant aeration rate
(300 rev min−1, 2.5 l min−1). 相似文献
7.
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
8.
Zohra Chikh Nguyêt-Thanh Ha-Duong Geneviève Miquel Jean-Michel El Hage Chahine 《Journal of biological inorganic chemistry》2007,12(1):90-100
The kinetics and thermodynamics of Ga(III) exchange between gallium mononitrilotriacetate and human serum transferrin as well
as those of the interaction between gallium-loaded transferrin and the transferrin receptor 1 were investigated in neutral
media. Gallium is exchanged between the chelate and the C-site of human serum apotransferrin in interaction with bicarbonate
in about 50 s to yield an intermediate complex with an equilibrium constant K
1 = (3.9 ± 1.2) × 10−2, a direct second-order rate constant k
1 = 425 ± 50 M−1 s−1 and a reverse second-order rate constant k
−1 = (1.1 ± 3) × 104 M−1 s−1. The intermediate complex loses a single proton with proton dissociation constant K
1a = 80 ± 40 nM to yield a first kinetic product. This product then undergoes a modification in its conformation which lasts
about 500 s to produce a second kinetic intermediate, which in turn undergoes a final extremely slow (several hours) modification
in its conformation to yield the gallium-saturated transferrin in its final state. The mechanism of gallium uptake differs
from that of iron and does not involve the same transitions in conformation reported during iron uptake. The interaction of
gallium-loaded transferrin with the transferrin receptor occurs in a single very fast kinetic step with a dissociation constant
K
d = 1.10 ± 0.12 μM and a second-order rate constant k
d = (1.15 ± 0.3) × 1010 M−1 s−1. This mechanism is different from that observed with the ferric holotransferrin and suggests that the interaction between
the receptor and gallium-loaded transferrin probably takes place on the helical domain of the receptor which is specific for
the C-site of transferrin and HFE. The relevance of gallium incorporation by the transferrin receptor-mediated iron-acquisition
pathway is discussed. 相似文献
9.
Isabel A. Lüthy Enrique T. Segura Viviana I. Lüthy Eduardo H. Charreau Ricardo S. Calandra 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1985,155(5):611-614
Summary (125I)-ovine prolactin (oPRL) binding was found in several brain areas of the toad,Bufo arenarum Hensel. The olfactory bulb, cerebral hemispheres, and both dorsal and ventral mesencephalic regions showed saturable, high
affinity, (125I)-oPRL binding, ranging between 5.6 to 29.9 fmol/mg protein, while the association constant (K
a) by Scatchard analysis was between 4.0 to 8.7×109 M−1. This binding was compared with the Scatchard plot of the kidney, which has been already described by other groups, and gave
41.7 fmol/mg protein andK
a 2.5×109 M−1. Liver showed no binding and in the cerebral hemispheres (125I)-oPRL was not displaced by non-lactogenic hormones, indicating that binding was hormone and tissue specific. 相似文献
10.
Jesús Adolfo Jiménez Nieves Alonso-Blázquez Dolores López-Vela Cristina Celestino Mariano Toribio Jesus Alegre 《In vitro cellular & developmental biology. Plant》2011,47(5):578-588
Somatic embryogenesis can be induced in the leaves of cork oak (Quercus suber L.) trees. The use of this propagation system in multivarietal forestry requires the mass production of cloned plants at
low cost. Investigations were made into the influence of three types of Erlenmeyer flask and three orbiting speeds (60, 110,
and 160 rpm) on oxygen transfer rate (KL
a), the shear force index (SFI), biomass production, and the proliferation of embryogenic clumps (EMCs) in cultures during
the proliferation phase. KL
a varied between 0.11 and 1.47 h−1 without biomass production being limited by oxygen availability. The EMCs grew even in hypoxic conditions, although the suppression
of gaseous exchange strongly reduced biomass production. Cultures with different levels of hydrodynamic stress and SFI values
(1.4·10−3–8.8·10−3 cm min−1) were obtained. Proliferation rates of EMCs increased with agitation rate and the SFI. The largest number of EMCs was obtained
in baffled flasks agitated at 160 rpm (KL
a of 1.47 h−1, and SFI of 8.8·10−3 cm min−1) with mild hydrodynamic stress enhancing growth. Biomass production increased with agitation and hydrodynamic stress, but
only when the SFI value was below 5·10−3 cm min−1. The greatest biomass production was obtained in smooth 100 ml flasks agitated at 160 rpm. The differentiation of embryos
was favoured by the lowest KL
a (0.11 h−1) and SFI (1.40·103 cm min−1) values, achieved using these flasks when agitated at 60 rpm. 相似文献
11.
Qingxin Zhao Sheng Yuan Yuling Zhang Hong Zhu Chuanchao Dai Fang Yang Fengmin Han 《World journal of microbiology & biotechnology》2007,23(8):1057-1064
Pectate lyase A (PelA) of Aspergillus nidulans was successfully expressed in Escherichia coli and effectively purified using a Ni2+-nitrilotriacetate-agarose column. Enzyme activity of the recombinant PelA could reach 360 U ml−1 medium. The expressed PelA exhibited its optimum level of activity over the range of pH 7.5–10 at 50°C. Mn2+, Ca2+, Fe2+, Mg2+ and Fe3+ ions stimulated the pectate lyase activity, but Cu2+ and Zn2+ inhibited it. The recombinant PelA had a V
max of 77 μmol min−1 mg−1 and an apparent K
m of 0.50 mg ml−1 for polygalacturonic acid. Low-esterified pectin was the optimum substrate for the PelA, whereas higher-esterified pectin
was hardly cleaved by it. PelA efficiently macerated mung bean hypocotyls and potato tuber tissues into single cells. 相似文献
12.
Optical fractionation of chlorophyll and primary production for coastal waters of the Southern Ocean 总被引:1,自引:1,他引:0
Our objective was to quantify the potential variability in remotely sensed chlorophyll a (Chl a) and primary productivity in coastal waters of the Southern Ocean. From data collected throughout the springs/summers of
1991–1994, we calculated the proportion of water column Chl a and primary productivity within the upper optical attenuation length (K −1
par) and the satellite-weighted depth. The temporal variability was resolved every 2–3 days and was observed to be greater within
years than between years. Three-year averages (n=223) revealed that 10.2 ± 3.6% of total Chl a and 14.8 ± 6.5% of production occurred within satellite-weighted depth in predominantly Case I waters. The average values
were twice as high within K −1
par, 24.1 ± 8% of total Chl a and 34 ± 9% of production respectively. Masked in these long-term averages are very large changes occurring on short time
scales of seasonal blooms. We observed that the patterns of Chl a vertical distribution within blooms are also subject to taxonomic influence and dependent upon the physiological state of
the phytoplankton. Highest proportions of water column Chl a in the first optical depth were measured during the rapid onset of surface cryptophyte blooms each year, i.e. 50% within
K −1
par and 30% above the satellite-weighted depth. Lowest fractions, 6% and 2% of biomass within K −1
par and satellite-weighted depth respectively, were associated with peak bloom conditions independent of taxonomy. Our analyses
suggest that satellite-dependent models of Chl a and subsequent chlorophyll-dependent primary production will be challenging to develop for the near-shore Southern Ocean,
especially given the potentially high natural variability in the vertical distribution of Chl a driven by physical forcing, the photoadaptive abilities of polar phytoplankton, and taxonomic influences.
Accepted: 27 August 1999 相似文献
13.
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
14.
Imura T Ito S Azumi R Yanagishita H Sakai H Abe M Kitamoto D 《Biotechnology letters》2007,29(6):865-870
A carbohydrate ligand system has been developed which is composed of self-assembled monolayers (SAMs) of mannosylerythritol
lipid-A (MEL-A) from Pseudozyma antarctica, serving for human immunoglobulin G and M (HIgG and HIgM). The estimated binding constants from surface plasmon resonance
(SPR) measurement were K
a = 9.4 × 106 M−1 for HIgG and 5.4 × 106 M−1 for HIgM, respectively. The binding site was not in the Fc region of immunoglobulin but in the Fab region. Large amounts
of HIgG and HIgM bound to MEL-A SAMs were directly observed by atomic force microscopy. 相似文献
15.
The study comprises a data set of CTD, optical properties—K
0(PAR), c
p, a(PAR), b(PAR)—and optical constituents—Chl a, SPM, CDOM—from 72 shelf and off-shelf stations in the Faroe Islands (62°N, 7°W) North East Atlantic, in early spring 2005.
Results showed that shelf waters surrounding the islands were cold and low saline, whereas off-shelf waters were warmer (~1°C)
and more saline (~0.05) PSU. A pronounced oceanographic front separated the two waters, and diffuse light attenuation K
0(PAR), beam attenuation c
p, Chl a, absorption a(PAR), and scattering coefficient b(PAR) were all significantly higher on the shelf. Analyses showed that off-shelf light attenuation K
0(PAR) was governed by Chl a, shown by a high (r
2 = 0.64) Chl a–K
0(PAR) correlation, whereas light attenuation on the shelf was governed by both Chl a, SPM, and CDOM in combination. A Chl a specific diffuse attenuation coefficient
K0* ( \textPAR ) K_{0}^{*} \left( {\text{PAR}} \right) of 0.056 (m2 mg−1 Chl a) and a Chl a specific beam attenuation (
c\textp* c_{\text{p}}^{*} ) of 0.27 (m2 mg−1 Chl a) coefficients were derived for the off-shelf. It is pointed out that Chl a is the single variable that changes over time as no rivers with high SPM and CDOM enter the shelf area. Data were obtained
in early spring, and Chl a concentrations were low ~0.5 mg Chl a m−3. Spring bloom Chl a are about 10 mg Chl a m−3 and estimations showed that shelf K
0(PAR) will increase about 5 times and beam attenuation about 10 times. The Faroe Islands shelf–off-shelf waters is a clear
example where physical conditions maintain some clear differences in optical properties and optical constituents. The complete
data set is enclosed. 相似文献
16.
Kanakis CD Tarantilis PA Polissiou MG Diamantoglou S Tajmir-Riahi HA 《Cell biochemistry and biophysics》2007,49(1):29-36
In this report we are examining how the antioxidant flavonoids can prevent DNA damage and what mechanism of action is involved
in the process. Flavonoids are strong antioxidants that prevent DNA damage. The anticancer and antiviral activities of these
natural products are implicated in their mechanism of actions. We study the interactions of quercetin (que), kaempferol (kae),
and delphinidin (del) with DNA and transfer RNA in aqueous solution at physiological conditions, using constant DNA or RNA
concentration 6.25 mmol (phosphate) and various pigment/polynucleotide(phosphate) ratios of 1/65 to 1 (DNA) and 1/48 to 1/8
(tRNA). The structural analysis showed quercetin, kaempferol, and delphinidin intercalate DNA and RNA duplexes with minor
external binding to the major or minor groove and the backbone phosphate group with overall binding constants for DNA adducts
K
que = 7.25 (±0.65) × 104 M−1, K
kae = 3.60 (±0.33) × 104 M−1, and K
del = 1.66 (±0.25) × 104 M−1 and for tRNA adducts K
que = 4.80 (±0.50) × 104 M−1, K
kae = 4.65 (±0.45) × 104 M−1, and K
del = 9.47 (±0.70) × 104 M−1. The stability of adduct formation is in the order of del>que>kae for tRNA and que>kae>del for DNA. Low flavonoid concentration
induces helical stabilization, whereas high pigment content causes helix opening. A partial B to A-DNA transition occurs at
high drug concentration, while tRNA remains in A-family structure. The antioxidant activity of flavonoids changes in order
delphinidin>quercetin>kaempferol. The results show intercalated flavonoids can make them strong antioxidants to protect DNA
from harmful free radical reactions. 相似文献
17.
Purification and properties of betaine aldehyde dehydrogenase from<Emphasis Type="Italic"> Avena sativa</Emphasis> 总被引:3,自引:0,他引:3
Livingstone JR Maruo T Yoshida I Tarui Y Hirooka K Yamamoto Y Tsutui N Hirasawa E 《Journal of plant research》2003,116(2):133-140
Betaine aldehyde dehydrogenase (BADH; EC 1.2.1.8) is the enzyme that catalyzes the second step in the synthesis of the osmoprotectant,
glycine betaine. NAD-dependent BADH was purified from Avena sativa shoots by DEAE Sephacel, hydroxyapatite, 5′-AMP Sepharose 4B, Mono Q and TSK-GEL column chromatographies to homogeneity by
the criterion of native PAGE, and the properties of BADH were compared with those of aminoaldehyde dehydrogenase purified
to homogeneity from A. sativa. The molecular mass estimated by both gel filtration using TSK-GEL column and Sephacryl S-200 was 120 and 115, kDa, respectively.
The enzyme is a homodimer with a subunit molecular mass of 61 kDa as shown by SDS-PAGE. The pI value of the enzyme was found
to be 6.3. The purified enzyme catalyzed not only the oxidation of betaine aldehyde (BAL), but also that of aminoaldehydes,
3-aminopropionaldehyde (APAL), 4-aminobutyraldehyde (ABAL), and 4-guanidinobutyraldehyde (GBAL). The K
m values for BAL, APAL, ABAL and GBAL were 5×10−6, 5.4×10−7, 2.4×10−5 and 5×10−5 M, respectively. APAL showed substrate inhibition at a concentration of 0.1 mM. A fragment of BADH cleaved by V8 protease
shared homology with other plant BADHs.
Electronic Publication 相似文献
18.
Madanala R Gupta V Deeba F Upadhyay SK Pandey V Singh PK Tuli R 《Biotechnology letters》2011,33(10):2057-2063
A gene from Withania somnifera (winter cherry), encoding a highly stable chloroplastic Cu/Zn superoxide dismutase (SOD), was cloned and expressed in Escherichia coli. The recombinant enzyme (specific activity of ~4,200 U mg−1) was purified and characterized. It retained ~90 and ~70% residual activities after 1 h at 80 and 95°C, respectively. At
95°C, thermal inactivation rate constant (K
d) of the enzyme was 2.46 × 10−3 min−1 and half-life of heat inactivation was 4.68 h. The enzyme was stable against a broad pH range (2.5–11.0). It also showed
a high degree of resistance to detergent, ethanol and protease digestion. This recombinant Cu/Zn SOD could therefore have
useful applications. 相似文献
19.
Thanaporn Laothanachareon Verawat Champreda Pornpimol Sritongkham Mithran Somasundrum Werasak Surareungchai 《World journal of microbiology & biotechnology》2008,24(12):3049-3055
Cross-linked enzyme crystals of organophosphate hydrolase (CLEC-OPH) prepared from crude recombinant E. coli cell lysate was used for the development of an electrochemical biosensor for the detection of organophosphate pesticides.
CLEC-OPH showed an increased V
max of 0.721 U mg protein−1 and a slightly lower K
m of 0.083 mM on paraoxon compared to the crude enzyme, resulting in an improved catalytic efficiency (k
cat/K
m = 4.17 × 105 M−1 min−1) with a remarkable increase on thermostability. An amperometric biosensor was constructed based on glutaraldehyde and albumin
cross-linkage of CLEC-OPH with carbon nanotubes. The sensor exhibited greater sensitivity and operational stability with a
lower limit of detection when compared with a sensor using an equivalent loading of crude OPH in a non-crystal form. The application
of crude enzyme-based CLEC would offer a simple and economical approach for the fabrication of efficient electrochemical biosensors. 相似文献
20.
M. Salam N. Dahiya R. Sharma S. K. Soni G. S. Hoondal R. Tewari 《Indian journal of microbiology》2008,48(3):358-364
A chitinase producing bacterium Enterobacter sp. NRG4, previously isolated in our laboratory, has been reported to have a wide range of applications such as anti-fungal
activity, generation of fungal protoplasts and production of chitobiose and N-acetyl D-glucosamine from swollen chitin. In
this paper, the gene coding for Enterobacter chitinase has been cloned and expressed in Escherichia coli BL21(DE3). The structural portion of the chitinase gene comprised of 1686 bp. The deduced amino acid sequence of chitinase
has high degree of homology (99.0%) with chitinase from Serratia marcescens. The recombinant chitinase was purified to near homogeneity using His-Tag affinity chromatography. The purified recombinant
chitinase had a specific activity of 2041.6 U mg−1. It exhibited similar properties pH and temperature optima of 5.5 and 45°C respectively as that of native chitinase. Using
swollen chitin as a substrate, the Km, kcat and catalytic efficiency (kcat/Km) values of recombinant chitinase were found to be 1.27 mg ml−1, 0.69 s−1 and 0.54 s−1M−1 respectively. Like native chitinase, the recombinant chitinase produced medicinally important N-acetyl D-glucosamine and
chitobiose from swollen chitin and also inhibited the growth of many fungi. 相似文献