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1.
Evaporation of water from the cell surface of the internode ofChara corallina was not affected by HgCl2 which is known to inhibit water channels. This makes a sharp contrast to the fact that most of osmotically driven water transport
is inhibited by HgCl2. Also in radish hypocotyls whose epidermis had been peeled off, evaporation of water was not inhibited by HgCl2, while osmotic water transport was significantly inhibited.
The cell wall tube was prepared by squeezing out the content of theChara internode. The rate of evaporation from the cell wall tube filled with 150 mM KCl was almost equal to that from the living
cell. The apparent hydraulic conductivity of the cell calculated from evaporation rate was found to be 1–2×10−3 pm s−1 Pa−1 which is about 1/1000 times the hydraulic conductivity of the plasma membrane (Lp) and 1/40 times the Lp under maximal inhibition with HgCl2.
It is concluded that under the relative humidity of 53–70% the rate of evaporation of water from the cell surface is limited
by the rate of evaporation from the cell wall which is so low that the loss of water can be supplemented without delay from
the cell interior across the plasma membrane even when water channels are completely closed. 相似文献
2.
Terence J. Evens Randall P. Niedz Gary J. Kirkpatrick 《Journal of applied phycology》2008,20(4):411-422
The microalga Haematococcus pluvialis Flotow has been the subject of a number of studies concerned with maximizing astaxanthin production for use in animal feeds
and for human consumption. Several of these studies have specifically attempted to ascertain the optimal temperature and irradiance
combination for growth of H. pluvialis, but there has been a great deal of disagreement between laboratories. “Ideal” levels of temperature and irradiance have
been reported to range from 14 to 28°C and 30 to 200 μmol photons m−2 s−1. The objective of the present study was to simultaneously explore temperature and irradiance effects for a single strain
of H. pluvialis (UTEX 2505) across an experimental region that encompassed the reported “optimal” combinations of these factors for multiple
strains. To this end, a two-dimensional experimental design based on response surface methodology (RSM) was created. Maximum
growth rates for UTEX 2505 were achieved at 27°C and 260 μmol photons m−2 s−1, while maximum quantum yield for stable charge separation at PSII (Fv/Fm) was achieved at 27°C and 80 μmol photons m−2 s−1. Maximum pigment concentrations correlated closely with maximum Fv/Fm. Numeric optimization of growth rate and Fv/Fm produced an optimal combination of 27°C and 250 μmol photons m−2 s−1. Polynomial models of the various response surfaces were validated with multiple points and were found to be very useful
for predicting several H. pluvialis UTEX 2505 responses across the entire two-dimensional experimental design space. 相似文献
3.
Osmotic water permeability of isolated vacuoles 总被引:5,自引:0,他引:5
We measured the osmotic water permeability (P
os) of vacuoles isolated from onion (Allium cepa L.), rape (Brassica napus L.), petunia (Petunia hybrida Hook.) and red beet (Beta vulgaris L.). For all the vacuolar types investigated, P
os values were in the range 200–1000 μm s−1. The change in membrane surface area induced by an osmotic gradient was smaller than 2–6%. The vacuolar P
os values for red beet and onion were reduced by 1 mM HgCl2, to 14% and 30% of the control values, respectively, but were partially restored to 51% and 76% by 5 mM β-mercaptoethanol.
These results suggest that aquaporins were present in all the vacuoles tested. In HgCl2-treated onion vacuoles, the reduced P
os (56 μm s−1) had a low activation energy (approx. 6 kJ mol−1), indicating that water permeation was still occurring mainly via aquaporins, and that the water permeability of the lipid
part of the vacuolar membrane is probably very low.
Received: 18 February 1999 / Accepted: 21 June 1999 相似文献
4.
In view of the increasing evidence that multicomponent diffusion effects could be significant in biological gas exchange systems,
a non-equimolar film model of multicomponent diffusion was derived. “Osmotic” ternary diffusion was studied for the gas systems
He−N2−O2, He−SF6−O2, and N2−SF6−O2. Diffusional fluxes and concentration profiles were calculated under both the “square-root” and the “product” flux conditions.
Results were also compared with those obtained using the equimolar flux condition. It was found that the greater the difference
of the diffusibilities between the two active components in a system, the greater the osmotic fluxes, and also the more alinear
the concentration profiles. These results support the suggestion that the “product” condition applies to molecular diffusion
in free space, the “square-root” condition to molecular diffusion in pores, and the equimolar flux condition to closed diffusion
systems. 相似文献
5.
The binding and unbinding constants describing interaction of ω-CTx-GVIA with N-type Ca2+ channels were calculated based on the time course of the blocking action of the toxin. The experiments were carried out on
pyramidal neurons freshly dissociated from theCA3 region of the rat hippocampus using a “concentration-clamp” technique and a patch-clamp technique in the whole-cell configuration.
The bindingk
1 and unbindingk
−1 constants were evaluated as 0.32 (μM·sec)−1 and 0.004 sec−1, respectively. The dissociation constantK
D kinetically derived from the ratiok
−1/k
1 was 0.012 μM. These values allow us to interpret the apparent “irreversibility” of the toxin action. 相似文献
6.
Tamara Pustovoitova 《Biologia Plantarum》1987,29(5):338-341
Effect of abscisic acid on cell permeability in leaves ofIresine u allisi hort. and roots ofBeta vulgaris L. were examined. An increase of betacyanin leakage from leaf cells was shown by ABA at 10−4, 10−7 or 10−9 M concentrations in water solution at 25 °C. The efflux of batacyanin from tissues did not change during the joint action
of ABA and PEG 1000. ABA could lower the betacyanin leakage fromIresine leaves and beet-root slices under severe osmotic stress, as was found by deplasmolysis. The results suggest that ABA elicits
some alteration in density of tonoplast membranes under dehydration.
Presented at the International Symposium “Plant Growth Regulators” held on June 18–22, 1984 at Liblice, Czechoslovakia. 相似文献
7.
S. O. Zhuravleva A. V. Sotkis D. S. Isaev A. V. Eremin A. N. Tarasenko P. G. Kostyuk Ya. M. Shuba 《Neurophysiology》1998,30(4-5):194-198
Low voltage-activated (LVA) Ca2+ conductances were characterized in the neurons of the associative laterodorsal (LD) thalamic nucleus in rat brain slices
and in enzymatically isolated thalamic units using electrophysiological techniques. Voltage dependence, kinetics of inactivation,
pharmacology, and selectivity of the LVA current in the thalamic neurons from animals older than 14 postnatal days were consistent
with the existence of two, “fast” and “slow,” subtypes of LVA Ca2+ channels. “Slow” LVA current in enzymatically isolated thalamic neurons was much less prominent, compared with that in slice
neurons, suggesting that respective channels are predominatly located on the distal dendrites. “Fast” Ca2+ channels were sensitive to nifedipine (K
d−2.6 μM) and La3+ (K
d−1.0 mM), whereas “slow” Ca2+ channels were sensitive to Ni2+ (25 μM). Selectivity of the “fast” Ca2+ channels was similar to that found for the LVA Ca2+ channels in other preparations (I
Ca:I
Sr:I
Ba−1.0: 1.23: 0.94), while selectivity of the “slow” Ca2+ channels more resembled selectivity of the HVA Ca2+ channels (I
Ca:I
Sr:I
Ba−1.0: 2.5: 3.4). 相似文献
8.
E. V. Navolotskaya T. A. Zargarova T. N. Lepikhova V. L. Turobov R. I. Nurieva N. V. Malkova V. P. Zav’yalov V. M. Lipkin 《Russian Journal of Bioorganic Chemistry》2000,26(1):27-33
The antiproliferative and immunosuppressivein vitro effects ofimmunocortin, a synthetic adrenocorticotropin-like (ACTH-like) decapeptide H-Val-Lys-Lys-Pro-Gly-Ser-Ser-Val-Lys-Val-OH, whose sequence
corresponds to segment 11–20 of the variable part of the human IgG1 heavy chain, were studied. At concentrations of 10−11−10−7 M, immunocortin was found to inhibit the growth of the human MT-4 T-lymphoblastoid cell line, to suppress the blast transformation
of thymocytes, and to decrease the spontaneous mobility of peritoneal macrophages and their bactericidal action toward the
virulent strainSalmonella typhimurium 415. By using a125I-labeled “addressing” fragment of ACTH {[125I]ACTH (13–24)}, we showed that MT-4 cells express specific receptors for ACTH (K
d 97 pM). Immunocortin and human ACTH (but not the heavy chain of IgG1) competitively inhibited the binding of [125I]ACTH-(13–24) to these receptors withK
i1 of 0.38 andK
i2 of 0.34 nM, respectively. Specific receptors for ACTH (K
d 5.8 nM) on mouse thymocytes were detected and characterized. The unlabeled immunocortin was shown to compete with labeled
ACTH-(13–24) for binding to these receptors (K
i=1.8 nM), and this binding of immunocortin to receptors on thymocytes activates adenylate cyclase from these cells and increases
the intracellular concentration of cAMP. 相似文献
9.
Mesozooplankton assemblages in the shallow Arctic Laptev Sea in summer 1993 and autumn 1995 总被引:2,自引:0,他引:2
Mesozooplankton distribution and composition in the very shallow part of the Siberian Laptev Sea shelf were studied during
the German-Russian expeditions “Transdrift I” (August/September 1993) and “Transdrift III” (October 1995). Maximum abundances
were found close to the outflow of the Lena River (7,965 ind. m−3) and in the Yana river mouth (38,163 ind. m−3). Lowest abundances occurred in the northeast and west of the Laptev Sea (64–95 ind. m−3). Highest biomass values (104–146 mg DM m−3) were determined in the northern and northeastern part of the shallow Laptev Sea, as well as close to the river outflows,
with a record biomass maximum in the Yana river mouth (270 mg DM m−3). Biomass minima were situated north of the Lena Delta and in the western part of the shallow Laptev Sea (0.3–1.0 mg DM m−3). Copepods dominated in terms of abundance and biomass. Cluster analyses separated four mesozooplankton assemblages: the
assemblage “Lena/Yana” in the southern part, “Eastern-central” in the centre, “Kotelnyy” in the eastern part and “Taimyr”
in the western part of the shallow Laptev Sea. The small-sized neritic and brackish-water copepods Drepanopus bungei, Limnocalanus grimaldii and Pseudocalanus major occurred in enormous numbers and made up the bulk of zooplankton abundance and biomass in the very shallow part of the Laptev
Sea close to the rivers Lena and Yana. In the more northern and northeastern areas, Calanus glacialis, P. minutus and P. major were dominant copepod species, whereas Oithona similis and Acartia sp. became important in the western Laptev Sea. Appendicularians, as well as hydromedusae and the chaetognath Sagitta sp., contributed significantly to abundance and biomass, respectively, but not over the entire area studied. One can identify
taxon-specific distribution patterns (e.g. Sagitta predominated the biomass in a zone between the area heavily influenced by Lena/Yana and the offshore area to the north),
which differ from the patterns revealed by cluster analysis. Hydrographic features, especially the enormous freshwater inflow,
apparently determine the occurrence and formation of zooplankton aggregations. Extremely high numbers of small-sized neritic
and brackish-water copepods occurred locally, which were probably also supported by excellent feeding conditions. 相似文献
10.
The objective of this article is to study the effect of 5-aminolevulinic acid (ALA) and enhanced chlorophyll content, antioxidative
enzymes and photosynthesis rate by foliar application of ALA. We evaluated three concentrations (control-distilled water,
T1-50 mg l−1, T2-150 mg l−1, T3-250 mg l−1) of ALA and seven cultivars, “Sanchidaye” (Sa-1), “Lichuandasuomian” (Li-1), “Aijiaohuang” (Ai-1), “Qingyou” No. 4 (Qi-1),
“Aikang” No. 5 (Ak-1), “Hanxiao” (Ha-1) and “Shulv” (Sl-1). “Ak-1” showed strongest response of POD (peroxidase) enzyme activity
(0.4 U g−1 min−1) in 250 mg l−1 ALA solution. The highest CAT (catalase) activity (0.8 U g−1 min−1) after administration of 250 mg l−1 ALA was observed in “Li-1”. Meanwhile, highest (1.42 mg l−1) total chlorophyll content was also observed in “Ak-1”, when leaves were treated in 50 mg l−1 ALA, “Li-1” and “Ai-1” showed strongest response of specific activity of superoxide dismutase (SOD) in 50 mg l−1 and 50 mg l−1 ALA. Two hundred and fifty milligram per milliliter of ALA-treatment significantly improved the net photosynthetic rate. 相似文献
11.
The estuarine red alga,Bostrychia radicans, was subjected to osmotic stresses ranging from hypo-osmotic (9.9‰) to hyperosmotic conditions (37.4‰). The growth rate decreased
with increasing salinities and showed a maximum in a mesohaline medium, while the photosynthetic rate and the chlorophyll
a content increased under hyper-osmotic conditions. The rate of respiration remained constant over the salinity range tested.B. radicans revealed typical characteristics of “shade plants” having a low light compensation point at 3–4 μE m−2 s−1 correlated with a low photon flux density of 70–100 μE m−2 s−1 for saturation of photosynthesis. These physiological properties may explain the success ofB. radicans in estuarine habitats. 相似文献
12.
Saba Ambreen Memon Xilin Hou Bo Zhu Joseph N. Wolukau 《Acta Physiologiae Plantarum》2009,31(6):1191-1196
The objective of the present work was selection of cultivar and suitable medium for regenerating shoots from leaf segments
of non-heading Chinese cabbage. We evaluated six types of supplemented media with 2.0, 5.0 and 10.0 mg l−1 6-BA; 1.0 and 2.0 mg l−1 TDZ; 0.1, 0.3, 0.5, 0.8 and 1.0 mg l−1NAA; 3.0, 5.0 and 7.5 mg l−1AgNO3; 0.01 mg l−1 2–4, D and 4.0 mg l−1 KT for shoot regeneration and six cultivars “Sanchidaye”, “Liuchuandasuomian”, “Qingyou 4”, “Liangbaiye”, “AiKang 5” and
“Hanxiao F3”, furthermore for root formation three types of supplemented media with 0.2, 0.3, 0.5 mg l−1 NAA, and for survival rate two types of base media: turf + vermiculite + manure (1:2:0.2) and soil + vermiculite (1:2). Culturing
leaf segments on MS medium supplemented with 2 mg l−1 TDZ; 0.5 mg l−1 NAA and 7.5 mg l−1 AgNO3 gave the highest number of shoots per leaf segment (66) while roots were best formed on the medium supplemented with 0.2 mg l−1 NAA. Survival rate was highest (61.6%) in the turf: vermiculite: manure (1:2:0.2) medium. The highest percentage of responding
leaf segments, number of shoots per leaf segment, rooting percentage and survival rate were observed in “Liuchuandasuomian”.
The plantlets were transferred to the soil and grown into mature plants in pots. These results could be used for preliminary
selections of cultivars to transfer disease resistance (Bt) gene through agrobacterium in non-heading Chinese cabbage. 相似文献
13.
Brush border membrane vesicles, BBMV, from eel intestinal cells or kidney proximal tubule cells were prepared in a low osmolarity
cellobiose buffer. The osmotic water permeability coefficient P
f
for eel vesicles was not affected by pCMBS and was measured at 1.6 × 10−3 cm sec−1 at 23°C, a value lower than 3.6 × 10−3 cm sec−1 exhibited by the kidney vesicles and similar to published values for lipid bilayers. An activation energy E
a
of 14.7 Kcal mol−1 for water transport was obtained for eel intestine, contrasting with 4.8 Kcal mol−1 determined for rabbit kidney proximal tubule vesicles using the same method of analysis. The high value of E
a
, as well as the low P
f
for the eel intestine is compatible with the absence of water channels in these membrane vesicles and is consistent with
the view that water permeates by dissolution and diffusion in the membrane. Further, the initial transient observed in the
osmotic response of kidney vesicles, which is presumed to reflect the inhibition of water channels by membrane stress, could
not be observed in the eel intestinal vesicles. The P
f
dependence on the tonicity of the osmotic shock, described for kidney vesicles and related to the dissipation of pressure
and stress at low tonicity shocks, was not seen with eel vesicles. These results indicate that the membranes from two volume
transporter epithelia have different mechanisms of water permeation. Presumably the functional water channels observed in
kidney vesicles are not present in eel intestine vesicles. The elastic modulus of the membrane was estimated by analysis of
swelling kinetics of eel vesicles following hypotonic shock. The value obtained, 0.79 × 10−3 N cm−1, compares favorably with the corresponding value, 0.87 × 10−3 N cm−1, estimated from measurements at osmotic equilibrium.
Received: 28 January 1999/Revised: 15 June 1999 相似文献
14.
A previously unknown genetic defect in magnesium metabolism (i.e., the magnesium-binding defect [MgBD]) was found to be associated
with the cause of “salt-sensitive” essential hypertension in humans and rats. It inhibits the entrance of Mg2+ into the cell so that the intracellular concentrations of Mg2+ and MgATP2− are decreased. Consequently, the 300 enzyme reactions in the cell, especially the 100 that either use or produce MgATP2−, are inhibited. Thus, because the extrusion of intracellular Na+ requires MgATP2−, hypertension results when the involved MgATP2− requiring enzyme is inhibited. The MgBD is corrected by the tachykinin substance P, which occurs in normal blood plasma,
and by the pentapeptide and its contained tetrapeptide, which are released from the C-terminal region of substance P by plasma
aminopeptidases. In vivo, the intravenous administration of the tetrapeptide corrects the hypertension and the MgBD as well.
The MgBD also occurs in type 2 diabetes mellitus and, thus, the decreased intracellular concentrations of Mg2+ and MgATP2− ions appear to be involved also in the cause of this disease, which is reputed to be the fifth most deadly disease in the
world. 相似文献
15.
M. D. Baustian S. Q. Wang K. W. Beyenbach 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(1):61-70
Plasma and urine of toadfish (Opsanus tau) in sea water and 10% sea water were analyzed to assess responses of an aglomerular fish to hypoosmotic challenge. Following
transfer to 10% sea water, plasma osmotic pressure decreased slowly from 318 to 241 mmol · kg H2O−1, over a period of 10–15 days. Urine osmotic pressure decreased in parallel from 299 to 207 mmol · kg H2O−1, leaving urine/plasma ratios of osmotic pressure essentially unchanged. In contrast, the volume and composition of urine
changed rapidly following transfer to 10% sea water. Urine flow rate increased 110% from 3.0 to 6.3 μl · 100g−1 · h−1 and Na+ excretion increased 346%, while excretion of Mg2− and SO4
2− decreased 81% and 90%, respectively. Excretion rates for Cl− were low in seawater toadfish and decreased further in 10% sea water. An unknown sulfur-containing anion, present in the
urine of seawater toadfish, contributed significantly to the composition and ionic balance in urine of toadfish in 10% sea
water. These results suggest that the inability to produce strongly dilute urine obliges toadfish to lose salt in order to
excrete water, in hypoosmotic media. The decrease in plasma osmotic pressure may be both a strategy to reduce osmotic and
ionic gradients in dilute media and a consequence of the kidney's inability to excrete water without salt.
Accepted: 22 August 1996 相似文献
16.
Wood CM Pärt P 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2000,170(3):175-184
The influence of a CO2/HCO−
3-buffered medium on intracellular pH regulation of gill pavement cells from freshwater rainbow trout was examined in monolayers
grown in primary culture on glass coverslips; intracellular pH (pHi) was monitored by continuous spectrofluorometric recording from cells loaded with 2′,7′-bis(2-carboxyethyl)-5(6)-carboxy-fluoroscein. When cells in HEPES-buffered medium at normal pH=7.70 were transferred to normal
CO2/HCO−
3-buffered medium {P
CO2=3.71 mmHg, [HCO−
3]= 6.1 mmol l−1, extracellular pH (pHe)=7.70}, they exhibited a brief acidosis but subsequently regulated the same pHi (∼7.41) as in HEPES. Buffer capacity (β)
increased by the expected amount (5.5–8.0 slykes) based on intracellular [HCO−
3], and was unaffected by most drugs and treatments. However, after transfer to high P
CO2=11.15 mmHg, [HCO−
3]= 18.2 mmol l−1 at the same pHe=7.70, the final regulated pHi was elevated (∼7.53). The rate of correction of alkalosis caused by washout of this high P
CO2, high-HCO−
3 medium was unaffected by removal of extracellular Cl−. Removal of extracellular Na+ lowered resting pHi and greatly inhibited the rate of pHi recovery from acidosis. Bafilomycin A1 (3 μmol l−1) had no effect on these responses. However amiloride (0.2 mmol l−1) inhibited recovery from acidosis caused by washout of an ammonia prepulse, but did not affect resting pHi, the latter differing from the response in HEPES where amiloride also lowered resting pHi. Similarly 4-acetamido-4′- isothiocyanatostilbene-2,2′-disulfonic acid, sodium salt (0.1 mmol l−1) did not affect resting pHi but slowed the rate of recovery from acidosis, though to a lesser extent than amiloride. Removal of extracellular Cl− also slowed the rate of recovery but greatly increased β by an unknown mechanism; when this was taken into account, H+ extrusion rate was unaffected. These results are consistent with the presence of Na+-(HCO−
3)N co-transport and/or Na+-dependent HCO−
3/Cl− exchange, in addition to Na+/H+ exchange, as mechanisms contributing to “housekeeping” pHi regulation in gill cells in CO2/HCO−
3 media, whereas only Na+/H+ exchange is seen in HEPES. Both Na+-independent Cl−/HCO−
3 exchange and V-type H+-ATPase mechanisms appear to be absent from these cells cultured in isotonic media.
Accepted: 30 November 1999 相似文献
17.
Claus Wittpoth Peter G. Kroth Katharina Weyrauch Klaus V. Kowallik Heinrich Strotmann 《Planta》1998,206(1):79-85
A protocol for the isolation of intact plastids from two marine centric diatoms, Odontella sinensis (Greville) Grunow and Coscinodiscus granii Gough, has been worked out. The cells were broken in a Yeda Press, and the intact plastids were purified by centrifugation
in Percoll gradients. Electron microscopy indicates that at least one of the four envelope membranes is present in the isolated
plastids. The plastids are photosynthetically active as proven by CO2 fixation which was measured by light-dependent oxygen evolution. Rates up to 50 μmol O2 · (mg Chl)−1 · h−1, i.e. about 40% of the in vivo rate of photosynthesis were obtained. The inhibition of CO2 fixation by external phosphate and the ability of the plastids to reduce added 3-phosphoglycerate photosynthetically indicate
the presence of a phosphate translocator in the envelope of the diatom plastids. Light-dependent O2 evolution upon addition of nitrite indicates the presence of nitrite reductase in these plastids. Purified envelope membranes
of Odontella plastids analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis contain polypeptides similar to those of the
envelope of higher-plant chloroplasts. However, there are additional bands present, which in part may be constituents of the
two additional envelope membranes (“chloroplast endoplasmic reticulum”) and in part may represent additional components of
the inner membranes.
Received: 1 August 1997 / Accepted: 2 February 1998 相似文献
18.
Savvas P. Tokmakidis Luc A. Léger Theophilos C. Pilianidis 《European journal of applied physiology and occupational physiology》1998,77(4):333-342
The purpose of this study was to compare various methods and criteria used to identify the anaerobic threshold (AT), and
to correlate the AT obtained with each other and with running performance. Furthermore, a number of additional points throughout
the entire range of lactate concentrations [La−] were obtained and correlated with performance. A group of 19 runners [mean age 33.7 (SD 9.6) years, height 173 (SD 6.3)
cm, body mass 68.3 (SD 5.4) kg, maximal O2 uptake (V˙O2
max
) 55.2 (SD 5.9) ml · kg−1 · min−1] performed a maximal multistage treadmill test (1 km · h−1 every 3.5 min) with blood sampling at the end of each stage while running. All AT points selected (visual [La−], 4 mmol · l−1 [La−], 1 mmol · l−1 above baseline, log-log breakpoint, and 45° tangent to the exponential regression) were highly correlated one with another
and with performance (r > 0.90) even when there were many differences among the AT (P < 0.05). The additional points (ranging from 3 to 8 mmol · l−1 [La−], 1 to 6 mmol · l−1 [La−] above the baseline, and 30 to 70° tangent to the exponential curve of [La−]) were also highly correlated with performance (r > 0.90). These results failed to demonstrate a distinct AT because many points of the curve provided similar information.
Intercorrelations and correlations between AT and performance were, however, reduced when AT were expressed as the percentage
of maximal treadmill speed obtained at AT or percentage of V˙O2
max
. This would indicate that different attributes of aerobic performance (i.e. maximal aerobic power, running economy and endurance)
are measured when manipulating units. Thus, coaches should be aware of these results when they prescribe an intensity for
training and concentrate more on the physiological consequences of a chosen [La−] rather than on a “threshold”.
Accepted: 22 October 1997 相似文献
19.
Both native Trametes hirsuta laccase and the same laccase modified with palmytic chains to turn it more hydrophobic were prepared and studied with cyclic
voltammetry and Raman spectroscopy. Native laccase immobilized in the monoolein cubic phase was characterized with resonance
Raman spectroscopy, which demonstrated that the structure at the “blue” copper site of the protein remained intact. The diamond-type
monoolein cubic phase prevents denaturation of enzymes on the electrode surface and provides contact of the enzyme with the
electrode either directly or through the mediation by electroactive probes. Direct electron transfer for both laccases incorporated
into a lyotropic liquid crystal was obtained under anaerobic conditions, whereas bioelectrocatalytic activity was shown only
for the native enzyme. The differences in electrochemical behavior of native and hydrophobic laccase as well as possible mechanisms
of direct and mediated electron transfers are discussed. The Michaelis constant for 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonate)
diammonium salt (ABTS2−), K
Mapp, and the maximal current, I
max, for the native enzyme immobilized onto the electrode were estimated to be 0.24 mM, and 5.3 μA, respectively. The maximal
current density and the efficiency of the catalysis, I
max/K
Mapp, were found to be 73 μA cm−2 and 208.2 μA cm−2 mM−1, respectively, and indicated a high efficiency of oxygen electroreduction by the enzyme in the presence of ABTS2− in the cubic-phase environment. Rate constants were calculated to be 7.5 × 104 and 3.6 × 104 M−1 s−1 for native and hydrophobic laccase, respectively. 相似文献
20.
H. Zhang M. J. Wang L. Y. Hu S. H. Wang K. D. Hu L. J. Bao J. P. Luo 《Russian Journal of Plant Physiology》2010,57(4):532-539
Effects of NaHS, H2S donor, on germination and antioxidant metabolism in wheat (Triticum aestivum L.) seeds under osmotic stress were investigated. With the enhancement of osmotic stress, which was mimicked by PEG-6000,
the seed germination dropped gradually. NaHS treatment could promote wheat seed germination against osmotic stress in a dose-dependent
manner; while Na+ and other sulfur-containing components, such as S2−, SO42−, SO32−, HSO4− and HSO3−, were not able to improve seed germination as NaHS did, confirming H2S or HS− derived from NaHS contribute to the protective roles. Further experiments showed that NaHS treatment combined with PEG enhanced
the activities of amylase and esterase in comparison to PEG treatment alone. Alternatively, NaHS treatment significantly reduced
malondialdehyde and hydrogen peroxide accumulation in seeds. Significant enhancement of catalase and ascorbate peroxidase
activities and decrease in lipoxygenase activity were observed in NaHS treated seeds, while peroxidase and superoxide dismutase
activities were not affected as compared with the control. Furthermore, the H2S donor treatment could retain higher levels of endogenous H2S in wheat seeds under osmotic stress. These data indicated that H2S played a protective role in wheat seed against osmotic stress. 相似文献