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1.
Manish Kumar Tiwari Hee-Jung Moon Marimuthu Jeya Jung-Kul Lee 《Applied microbiology and biotechnology》2010,87(2):571-581
An NAD+-dependent xylitol dehydrogenase from Rhizobium etli CFN42 (ReXDH) was cloned and overexpressed in Escherichia coli. The DNA sequence analysis revealed an open reading frame of 1,044 bp, capable of encoding a polypeptide of 347 amino acid
residues with a calculated molecular mass of 35,858 Da. The ReXDH protein was purified as an active soluble form using GST
affinity chromatography. The molecular mass of the purified enzyme was estimated to be ∼34 kDa by sodium dodecyl sulfate–polyacrylamide
gel and ∼135 kDa with gel filtration chromatography, suggesting that the enzyme is a homotetramer. Among various polyols,
xylitol was the preferred substrate of ReXDH with a K
m = 17.9 mM and kcat
/K
m = 0.5 mM−1 s−1 for xylitol. The enzyme had an optimal pH and temperature of 9.5 and 70 °C, respectively. Heat inactivation studies revealed
a half life of the ReXDH at 40 °C of 120 min and a half denaturation temperature (T
1/2) of 53.1 °C. ReXDH showed the highest optimum temperature and thermal stability among the known XDHs. Homology modeling and
sequence analysis of ReXDH shed light on the factors contributing to the high thermostability of ReXDH. Although XDHs have
been characterized from several other sources, ReXDH is distinguished from other XDHs by its high thermostability. 相似文献
2.
Vesterdorf K Blache D Maloney SK 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2011,181(2):277-288
Panting is a mechanism that increases respiratory evaporative heat loss (REHL) under heat load. Because REHL uses body water,
it is physiologically and ecologically relevant to know under what conditions free-ranging animals use panting. We investigated
whether the cranial arterio-venous temperature difference could provide information about REHL. We exposed sheep to environments
varying in ambient dry bulb temperatures (Env 1: ~15°C, Env 2: ~25°C, Env 3: ~40°C, Env 4: ~40°C + infrared radiation) and
measured REHL simultaneously with carotid arterial (T
car) and jugular venous (T
jug) blood temperatures, as well as brain (T
brain) and rectal (T
rec) temperatures. REHL increased significantly with ambient temperature, from 18.4 ± 4.5 W at Env 1 to 79.5 ± 12.6 W at Env
4 (P < 10−6). While there was no effect of environment on T
car (P = 0.7) or T
jug (P = 0.09), the difference between them (T
a-v = T
car − T
jug) increased from Env 1 to Env 2 (P = 0.04) and from Env 3 to Env 4 (P = 0.008). T
a-v reached a maximum of 0.7 ± 0.2°C at Env 4 and was positively correlated with REHL across environments (r
2 = 0.78, F = 34.7, P < 10−3). Calculated cranial blood flow changed only from Env 2 to Env 3 (P = 0.002). The increase in REHL maintained homeothermy when dry heat loss decreased. While REHL could increase without generating
an increase in T
a-v, any increase in T
a-v was always associated with an increase in REHL. We conclude that the cranial T
a-v provides useful information about REHL in panting animals. 相似文献
3.
A nitrilase gene from Alcaligenes sp. ECU0401 was cloned and overexpressed in Escherichia coli BL21 (DE3) in a soluble form. The encoded protein with a His6-tag was purified to nearly homogeneity as revealed by SDS-PAGE with a molecular weight of approximately 38.5 kDa, and the
holoenzyme was estimated to be composed of 10 subunits of identical size by size exclusion chromatography. The V
max and K
m parameters were determined to be 27.9 μmol min−1 mg−1 protein and 21.8 mM, respectively, with mandelonitrile as the substrate. The purified enzyme was highly thermostable with
a half life of 155 h at 30 °C and 94 h at 40 °C. Racemic mandelonitrile (50 mM) could be enantioselectively hydrolyzed to
(R)-(−)-mandelic acid by the purified nitrilase with an enantiomeric excess of 97%. The extreme stability, high activity and
enantioselectivity of this nitrilase provide a solid base for its practical application in the production of (R)-(−)-mandelic acid. 相似文献
4.
The gene encoding a cold-active and xylose-stimulated β-glucosidase of Marinomonas MWYL1 was synthesized and expressed in Escherichia coli. The recombinant enzyme (reBglM1) was purified and characterized. The molecular mass of the purified reBglM1 determined by
SDS-PAGE agree with the calculated values (50.6 Da). Optima of temperature and pH for enzyme activity were 40°C and 7.0, respectively.
The enzyme exhibited about 20% activity at 5°C and was stable over the range of pH 5.5–10.0. The presence of xylose significantly
enhanced enzyme activity even at higher concentrations up to 600 mM, with maximal stimulatory effect (about 1.45-fold) around
300 mM. The enzyme is active with both glucosides and galactosides and showed high catalytic efficiency (k
cat = 500.5 s−1) for oNPGlc. These characterizations enable the enzyme to be a promising candidate for industrial applications. 相似文献
5.
A new polynitro cage compound with the framework of HNIW and a tetrazole unit, i.e., 10-(1-nitro-1, 2, 3, 4-tetraazol-5-yl))
methyl-2, 4, 6, 8, 12-hexanitrohexaazaisowurtzitane (NTz-HNIW) has been proposed and studied by density functional theory
(DFT) and molecular mechanics methods. Properties such as IR spectrum, heat of formation, thermodynamic properties, and crystal
structure were predicted. The compound belongs to the Pbca space group, with the lattice parameters a = 15.07 ?, b = 12.56 ?, c = 18.34 ?, Z = 8, and ρ = 1.990 g·cm-3. The stability of the compound was evaluated by the bond dissociation energies and results showed that the first step of
pyrolysis is the rupture of the N–NO2 bond in the side chain. The detonation properties were estimated by the Kamlet-Jacobs equations based on the calculated crystal
density and heat of formation, and the results were 9.240 km·s-1 for detonation velocity and 40.136 GPa for detonation pressure. The designed compound has high thermal stability and good
detonation properties and is probably a promising high energy density compound (HEDC). 相似文献
6.
Hartinger D Schwartz H Hametner C Schatzmayr G Haltrich D Moll WD 《Applied microbiology and biotechnology》2011,91(3):757-768
Fumonisins are carcinogenic mycotoxins that are frequently found as natural contaminants in maize from warm climate regions
around the world. The aminotransferase FumI is encoded as part of a gene cluster of Sphingopyxis sp. MTA144, which enables this bacterial strain to degrade fumonisin B1 and related fumonisins. FumI catalyzes the deamination of the first intermediate of the catabolic pathway, hydrolyzed fumonisin
B1. We used a preparation of purified, His-tagged FumI, produced recombinantly in Escherichia coli in soluble form, for enzyme characterization. The structure of the reaction product was studied by NMR and identified as
2-keto hydrolyzed fumonisin B1. Pyruvate was found to be the preferred co-substrate and amino group receptor (K
M = 490 μM at 10 μM hydrolyzed fumonisin B1) of FumI, but other α-keto acids were also accepted as co-substrates. Addition of the co-enzyme pyridoxal phosphate to the
enzyme preparation enhanced activity, and saturation was already reached at the lowest tested concentration of 10 μM. The
enzyme showed activity in the range of pH 6 to 10 with an optimum at pH 8.5, and in the range of 6°C to 50°C with an optimum
at 35°C. The aminotransferase worked best at low salt concentration. FumI activity could be recovered after preincubation
at pH 4.0 or higher, but not lower. The aminotransferase was denatured after preincubation at 60°C for 1 h, and the residual
activity was also reduced after preincubation at lower temperatures. At optimum conditions, the kinetic parameters K
M = 1.1 μM and k
cat = 104/min were determined with 5 mM pyruvate as co-substrate. Based on the enzyme characteristics, a technological application
of FumI, in combination with the fumonisin carboxylesterase FumD for hydrolysis of fumonisins, for deamination and detoxification
of hydrolyzed fumonisins seems possible, if the enzyme properties are considered. 相似文献
7.
Tyrammonium 4-nitrophthalate has been synthesized and its structural and spectroscopic properties elucidated by single-crystal
X-ray diffraction, solid-state polarized IR-spectroscopy of oriented colloids in a nematic host, HPLC with tandem mass spectrometry
(HPLC ESI-MSMS), and TGV and DSC methods. The compound crystallizes in the monoclinic P21/c space group and its structure consists of a 3D network of molecules joined by intermolecular interactions with the participation
of cations, anions and two solvent molecules. The tyrammonium cation adopts a T trans configuration with corresponding angles of ϕ
1 = 76.0(4)°, ϕ
2 = 54.8(1)° and ϕ
3 = 63.4(1)°, respectively. In the 4-nitrophthalate anion, the COO− and COOH groups are turned off the plane of the benzene ring at angles of τ
1 = 88.1(5)° and τ
2= 22.1(7)°, respectively. 相似文献
8.
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
9.
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
10.
Pratibha Dheeran Sachin Kumar Yogesh K. Jaiswal Dilip K. Adhikari 《Applied microbiology and biotechnology》2010,86(6):1857-1866
A newly isolated Geobacillus sp. IIPTN (MTCC 5319) from the hot spring of Uttarakhand's Himalayan region produced a hyperthermostable α-amylase. The microorganism
was characterized by biochemical tests and 16S rRNA gene sequencing. The optimal temperature and pH were 60°C and 6.5, respectively,
for growth and enzyme production. Although it was able to grow in temperature ranges from 50 to 80°C and pH 5.5–8.5. Maximum
enzyme production was in exponential phase with activity 135 U ml−1 at 60°C. Assayed with cassava as substrate, the enzyme displayed optimal activity 192 U ml−1 at pH 5.0 and 80°C. The enzyme was purified to homogeneity with purification fold 82 and specific activity 1,200 U mg−1 protein. The molecular mass of the purified enzyme was 97 KDa. The values of K
m
and V
max were 36 mg ml−1 and 222 μmol mg−1 protein min−1, respectively. The amylase was stable over a broad range of temperature from 40°C to 120°C and pH ranges from 5 to 10. The
enzyme was stimulated with Mn2+, whereas it was inhibited by Hg2+, Cu2+, Zn2+, Mg2+, and EDTA, suggesting that it is a metalloenzyme. Besides hyperthermostability, the novelty of this enzyme is resistance
against protease. 相似文献
11.
MA Giraldo TM da Silva F Salvato HF Terenzi JA Jorge LH Guimarães 《World journal of microbiology & biotechnology》2012,28(2):463-472
The filamentous fungus Paecylomices variotii was able to produce high levels of cell extract and extracellular invertases when grown under submerged fermentation (SbmF)
and solid-state fermentation, using agroindustrial products or residues as substrates, mainly soy bran and wheat bran, at
40°C for 72 h and 96 h, respectively. Addition of glucose or fructose (≥1%; w/v) in SbmF inhibited enzyme production, while
the addition of 1% (w/v) peptone as organic nitrogen source enhanced the production by 3.7-fold. However, 1% (w/v) (NH4)2HPO4 inhibited enzyme production around 80%. The extracellular form was purified until electrophoretic homogeneity (10.5-fold
with 33% recovery) by DEAE-Fractogel and Sephacryl S-200 chromatography. The enzyme is a monomer with molecular mass of 102 kDa
estimated by SDS–PAGE with carbohydrate content of 53.6%. Optima of temperature and pH for both, extracellular and cell extract
invertases, were 60°C and 4.0–4.5, respectively. Both invertases were stable for 1 h at 60°C with half-lives of 10 min at
70°C. Mg2+, Ba2+ and Mn2+ activated both extracellular and cell extract invertases from P. variotii. The kinetic parameters Km and Vmax for the purified extracellular enzyme corresponded to 2.5 mM and 481 U/mg prot−1, respectively. 相似文献
12.
A highly selective sucrose isomerase (SIase) was purified to homogeneity from the cell-free extract of Erwinia rhapontici NX-5 with a recovery of 27.7% and a fold purification of 213.6. The purified SIase showed a high specific activity of 427.1 U mg−1 with molecular weight of 65.6 kDa. The K
m for sucrose was 222 mM while V
max was 546 U mg−1. The optimum pH and temperature for SIase activity were 6.0 and 30 °C, respectively. The purified SIase was stable in the
temperature range of 10–40 °C and retained 65% of the enzyme activity after 2 weeks’ storage at 30 °C. The SIase activity
was enhanced by Mg2+ and Mn2+, inhibited by Ca2+, Cu2+, Zn2+, and Co2+, completely inhibited by Hg2+ and Ag2+. The purified SIase was strongly inhibited by SDS, while partially inhibited by dimethylformamide, tetrahydrofuran, and PMSF.
Additionally, glucose and fructose acted as competitive inhibitors for purified SIase. 相似文献
13.
Vikramathithan J Muthuraman P Ravikumar S Shayamala S Kumar GN Srikumar K 《The protein journal》2012,31(2):141-149
Two thermostable xylanase isoforms T60 and T80 were purified to homogeneity from the cladodes of the xerophytic Cereus pterogonus plant species. After three consecutive purification steps, the specific activity of T60 and T80 isoforms were found to be 178.6 and 216.2 U mg−1 respectively. The molecular mass of both isoforms was determined to be 80 kDa. The optimum temperature for T60 and T80 xylanase isoforms were 60 and 80 °C respectively. The pH was 5.0 for both isoforms. The presence of divalent metal ions (10 mM
Co2+) showed stimulatory effects of both catalytic activities, where as in the presence of Hg2+, Cd2+, Cu2+ showed inhibitory effect on these activities at all concentrations studied. The thermodynamic analysis of xylanase activity
using denaturation kinetics and the presence divalent cations at 30–100 °C, showed lower ΔH, ΔS, and ΔG values at all the temperatures investigated. The melting temperature of purified T80 xylanase isoform as determined by TG/DTA analysis and it showed the unfolding temperature was 80 °C. The g value and hyperfine
(A) value purified xylanase T80 isoform was 2.017 and 10.80 respectively. Immunoblot analysis with antiserum raised against the purified T80 xylanase isoforms revealed single immunolgically related polypeptides of 80 kDa, identical with the polypeptide band produced
on SDS-PAGE. The results of double immunodiffusion against the T80 isoforms showed a single precipitin line indicating that the serum used was specific to these xylanase isoforms. The kinetic
and thermodynamic properties suggested that xylanase from C. pterogonus may have a potential usage in various industries. 相似文献
14.
Asiya Nazir Rohit Soni H. S. Saini R. K. Manhas B. S. Chadha 《World journal of microbiology & biotechnology》2009,25(7):1189-1197
An endoglucanase (1, 4-β-d glucan glucanohydrolase, EC 3.2.1.4) which was catalytically more active and exhibited higher affinity towards barley β-glucan,
xyloglucan and lichenin as compared to carboxymethylcellulose (CMC) was purified from Aspergillus terreus strain AN1 following ion-exchange and hydrophobic interaction chromatography and gel filtration. The purified enzyme (40-fold) that
apparently lacked a cellulose-binding domain showed a specific activity of 60 μmol mg−1 protein−1 against CMC. The purified enzyme had a molecular weight of 78 and 80 KDa as indicated by sodium dodecyl sulphate–polyacrylamide
gel electrophoresis and gel filtration, respectively, and a pI of 3.5. The enzyme was optimally active at temperature 60°C
and pH 4.0, and was stable over a broad range of pH (3.0–5.0) at 50°C. The endoglucanase activity was positively modulated
in the presence of Cu2+, Mg2+, Ca2+, Na+, DTT and mercaptoethanol. Endoglucanase exhibited maximal turn over number (K
cat) and catalytic efficiency (K
cat/km) of 19.11 × 105 min−1 and 29.7 × 105 mM−1 min−1 against barley β-glucan as substrate, respectively. Hydrolysis of CMC and barley β-glucan liberated cellobiose, cellotriose,
cellotetraose and detectable amount of glucose. The hydrolysis of xyloglucan, however, apparently yielded positional isomers
of cellobiose, cellotriose and cellotetraose as well as larger oligosaccharides. 相似文献
15.
Christine E. Cooper Philip C. Withers 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2010,180(6):857-868
Quolls (Dasyurus) are medium-sized carnivorous dasyurid marsupials. Tiger (3,840 g) and eastern quolls (780 g) are mesic zone species, northern
quolls (516 g) are tropical zone, and chuditch (1,385 g) were once widespread through the Australian arid zone. We found that
standard physiological variables of these quolls are consistent with allometric expectations for marsupials. Nevertheless,
inter-specific patterns amongst the quolls are consistent with their different environments. The lower T
b of northern quolls (34°C) may provide scope for adaptive hyperthermia in the tropics, and they use torpor for energy/water
conservation, whereas the larger mesic species (eastern and tiger quolls) do not appear to. Thermolability varied from little
in eastern (0.035°C °C−1) and tiger quolls (0.051°C oC−1) to substantial in northern quolls (0.100°C oC−1) and chuditch (0.146°C oC−1), reflecting body mass and environment. Basal metabolic rate was higher for eastern quolls (0.662 ± 0.033 ml O2 g−1 h−1), presumably reflecting their naturally cool environment. Respiratory ventilation closely matched metabolic demand, except
at high ambient temperatures where quolls hyperventilated to facilitate evaporative heat loss; tiger and eastern quolls also
salivated. A higher evaporative water loss for eastern quolls (1.43 ± 0.212 mg H2O g−1 h−1) presumably reflects their more mesic distribution. The point of relative water economy was low for tiger (−1.3°C), eastern
(−12.5°C) and northern (+3.3) quolls, and highest for the chuditch (+22.6°C). We suggest that these differences in water economy
reflect lower expired air temperatures and hence lower respiratory evaporative water loss for the arid-zone chuditch relative
to tropical and mesic quolls. 相似文献
16.
G. M. Artmann Ilya Digel K. F. Zerlin Ch. Maggakis-Kelemen Pt. Linder D. Porst P. Kayser A. M. Stadler G. Dikta A. Temiz Artmann 《European biophysics journal : EBJ》2009,38(5):589-600
When aspirating human red blood cells (RBCs) into 1.3 μm pipettes (ΔP = −2.3 kPa), a transition from blocking the pipette below a critical temperature T
c = 36.3 ± 0.3°C to passing it above the T
c occurred (micropipette passage transition). With a 1.1 μm pipette no passage was seen which enabled RBC volume measurements
also above T
c. With increasing temperature RBCs lost volume significantly faster below than above a T
c = 36.4 ± 0.7 (volume transition). Colloid osmotic pressure (COP) measurements of RBCs in autologous plasma (25°C ≤ T ≤ 39.5°C) showed a T
c at 37.1 ± 0.2°C above which the COP rapidly decreased (COP transition). In NMR T1-relaxation time measurements, the T1 of RBCs in autologous plasma changed from a linear (r = 0.99) increment below T
c = 37 ± 1°C at a rate of 0.023 s/K into zero slope above T
c (RBC T1 transition). In conclusion: An amorphous hemoglobin–water gel formed in the spherical trail, the residual partial sphere
of the aspirated RBC. At T
c, a sudden fluidization of the gel occurs. All changes mentioned above happen at a distinct T
c close to body temperature. The T
c is moved +0.8°C to higher temperatures when a D2O buffer is used. We suggest a mechanism similar to a “glass transition” or a “colloidal phase transition”. At T
c, the stabilizing Hb bound water molecules reach a threshold number enabling a partial Hb unfolding. Thus, Hb senses body
temperature which must be inscribed in the primary structure of hemoglobin and possibly other proteins.
This article is dedicated to Ludwig Artmann who died on July 21, 2001 on a beautiful summer day during which we performed
experiments far away. Ludwig Artmann was a man who encouraged us to be strong and to study hard no matter what were the costs. 相似文献
17.
The protein bCblC (bCblCpro) is a bovine homolog of a human B12 trafficking chaperone that is responsible for the processing of vitamin B12 and its escorted delivery in intracellular B12 metabolism. In this study, we found that bCblCpro is highly thermolabile with a T
m = 42.0 ± 0.2 °C as shown for the human homolog, suggesting thermal regulation of these proteins. Binding of the reduced form
of glutathione (GSH) that is a predominant cellular thiol increased the T
m of bCblCpro from 42 °C to ~45 °C (ΔT
m max = 3.1 ± 0.2 °C and AC50 = 2.1 ± 0.5 mM). Binding of vitamin B12 and its derivatives also stabilized bCblCpro increasing the T
m to a different extent and vitamin B12 (cyanocobalamin, CNCbl) was the least efficient (ΔT
m max = 4.3 ± 0.3 °C and AC50 = 291 ± 36 μM). However, the stabilizing effect of CNCbl was significantly greater for GSH-bound bCblCpro (ΔT
m max = 12.8 ± 0.6 °C and AC50 = 9.3 ± 1.6 μM) than for GSH-free bCblCpro. In addition, the stabilizing effect of GSH was also greater for CNCbl-bound bCblCpro
(ΔT
m max = 9.3 ± 0.3 °C and AC50 = 57.0 ± 6.8 μM). Limited proteolysis revealed that thermal stabilization of bCblCpro is derived from conformational changes
of the protein induced by binding of the ligands. The results in this study indicate that GSH cooperates with vitamin B12 in thermal stabilization of bCblCpro and is a positive regulator of the protein. 相似文献
18.
Dlugokenski RE Sella SR Guizelini BP Vandenberghe LP Woiciechowski AL Soccol CR Minozzo JC 《Applied microbiology and biotechnology》2011,90(2):713-719
A novel low-cost medium was developed from by-products and wastes from the ethanol agro-industry to replace commercial media
in the production of a steam sterilization biological indicator (BI). Various recovery media were developed using soybean
or sugarcane molasses and vinasse to prepare a self-contained BI. Media performance was evaluated by viability and heat resistance
(D
121 °C value) according to regulatory standards. A medium produced with a soybean vinasse ratio of 1:70 (1.4%) (w/v) produced the results, with D
121 °C = 2.9 ± 0.5 min and Usk = 12.7 ± 2.1 min. The addition of 0.8% (w/v) yeast extract improved the germination of heat-damaged spores. The pH variation from 6.0 to 7.3 resulted in a gradual increase
in the D
121 °C value. The absence of calcium chloride resulted in a decrease in germination, while no significant differences were observed
with starch addition. Soybean vinasses may thus be used as the main component of a culture medium to substitute for commercial
media in the production of self-contained biological indicators. The use of ethanol production waste in this biotechnological
process realized a reliable performance, minimized the environmental impact, and decreased BI production costs while producing
a high quality product. 相似文献
19.
Wendy A. Wilson M. Justin O’Riain Robyn S. Hetem Andrea Fuller Linda G. Fick 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2010,180(7):1099-1110
The body temperature (T
b) of Cape ground squirrels (Xerus inauris, Sciuridae) living in their natural environment during winter has not yet been investigated. In this study we measured abdominal
T
b of eight free-ranging Cape ground squirrels over 27 consecutive days during the austral winter. Mean daily T
b was relatively stable at 37.0 ± 0.2°C (range 33.4 to 40.2°C) despite a marked variation in globe temperature (T
g) (range −7 to 37°C). Lactating females (n = 2) consistently had a significantly higher mean T
b (0.7°C) than non-lactating females (n = 3) and males. There was a pronounced nychthemeral rhythm with a mean active phase T
b of 38.1 ± 0.1°C and a mean inactive phase T
b of 36.3 ± 0.3°C for non-lactating individuals. Mean daily amplitude of T
b rhythm was 3.8 ± 0.2°C. T
b during the active phase closely followed T
g and mean active phase T
b was significantly correlated with mean active phase T
g (r
2 = 0.3–0.9; P < 0.01). There was no evidence for daily torpor or pronounced hypothermia during the inactive phase, and mean minimum inactive
phase T
b was 35.7 ± 0.3°C for non-lactating individuals. Several alternatives (including nocturnal huddling, an aseasonal breeding
pattern and abundant winter food resources) as to why Cape ground squirrels do not employ nocturnal hypothermia are discussed. 相似文献
20.
Wang Xi-Ling Zhou Jin-Xing Yu Mao-De Li Zhen-Gang Jin Xiao-Yun Li Qi-You 《In vitro cellular & developmental biology. Plant》2011,47(3):434-440
Efficient plant regeneration is essential for successful transformation and in vitro polyploidy induction in mulberry. A high frequency (80%) of plant regeneration from hypocotyls occurred under in vitro conditions in mulberry (Morus multicaulis Poir.). We identified three key factors for enhancing successful regeneration based on earlier work: (1) hypocotyl position,
(2) the combination and concentration of growth regulators, and (3) the addition of AgNO3. The highest frequency of shoot regeneration was achieved using hypocotyl segments, which are proximal to apical meristems,
and the optimal culture conditions were Murashige and Skoog’s (MS) (Murashige and Skoog, 1962) basal medium supplemented with 3.0 mg l−1 6-benzylamino purine, 0.3 mg l−1 indole-3-acetic acid, 0.1% polyvinypyrrolidone, and 1.0 mg/l silver nitrate (AgNO3) under subdued light at 25 ± 2°C. Treating the shoots with 0.2% colchicine (dipping for 72 h) resulted in a 14% tetraploid
frequency, whereas a 20% tetraploid frequency resulted from using a 0.25% colchicine (dripping for 5 d) treatment, as determined
by chromosome number counts. The diploid plant chromosome number was 28 (2n = 2x = 28) and that of tetraploid plants was 56 (2n = 4x = 56). Regenerated shoots rooted easily in 8–10 d using half-strength basal MS medium with 0.5 mg l−1 indole-3-butyric acid and were successfully established in the soil. 相似文献