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1.
Although grasses are commonly used to revegetate sites contaminated with lead (Pb), little is known regarding the Pb-tolerance
of many of these species. Using dilute solution culture to mimic the soil solution, the growth of signal grass (Brachiaria decumbens Stapf cv. Basilisk) and Rhodes grass (Chloris gayana Kunth cv. Pioneer) was related to the mean activity of Pb2+ {Pb2+} in solution. There was a 50% reduction in fresh mass of signal grass shoots at 5 μM {Pb2+} and at 3 μM {Pb2+} for the roots. Rhodes grass was considerably more sensitive to Pb in solution, with shoot and root fresh mass being reduced
by 50% at 0.5 μM {Pb2+}. The higher tolerance of signal grass to Pb appeared to result from the internal detoxification of Pb, rather than from
the exclusion of Pb from the root. At toxic {Pb2+}, an interveinal chlorosis developed in the shoots of signal grass (possibly a Pb-induced Mn deficiency), whilst in Rhodes
grass, Pb2+ caused a bending of the root tips and the formation of a swelling immediately behind some of the root apices. Root hair growth
did not appear to be reduced by Pb2+ in solution, being prolific at all {Pb2+} in both species. 相似文献
2.
A. Rehman Farah R. Shakoori A. R. Shakoori 《World journal of microbiology & biotechnology》2007,23(6):753-758
Summary The alga, Distigma proteus, isolated from industrial wastewater showed tolerance against Cd2+ (8.0 μg/ml), Cr6+ (12 μg/ml), Pb2+ (15 μg/ml) and Cu2+ (10 μg/ml). The metal ions slowed down the growth of the organism after 4–5 days of exposure. The reduction in cell population
was 90% for Cu2+, 84% for Cd2+, 71% for Cr6+, and 63% for Pb2+ after 8 days of metal stress. The order of resistance to heavy metal, in terms of reduction in the cellular population, was
Cu2+ > Cd2+ > Cr6+ > Pb2+. Chromium- and cadmium-processing capabilities of the alga were worked out for its potential use as a bioremediator of wastewater.
The reduction in the amount of Cr6+ after 2, 4, 6 and 8 days of algal culture containing 5.0 μg Cr6+ ml−1 of culture medium was 77, 85, 92 and 97%, respectively. Distigma could also remove 48% Cd2+after 2 days, 68% after 4 days, 80% after 6 days and 90% after 8 days from the medium. The heavy metal uptake ability of Distigma can be exploited for metal detoxification and environmental clean-up operations. 相似文献
3.
Moni Brauer Wen-Jun Zhong Till Jelitto Christian Schobert Dale Sanders Ewald Komor 《Planta》1998,206(1):103-107
Changes in free Ca2+ in sieve-tube sap have been proposed to be important in the regulation of phloem transport, and Ca2+-activated protein kinase activity has been described in phloem exudate (S.A. Avdiushko et al. 1997 J Plant Physiol 150: 552–559).
Using atomic absorption spectrometry, we have determined that the total Ca2+ concentration in sieve-tube sap from Ricinus seedlings containing the endosperm is about 100 μM (range 80–150 μM). We used
three independent methods to determine the free calcium ion concentration in the phloem sap ([Ca2+]p). The first method was to calculate [Ca2+]p from the total Ca2+ concentration, in combination with the binding constants and concentrations of the ionic solutes in phloem sap. The resultant
estimate of [Ca2+]p was 63 μM. The second method used the Ca-specific fluorescent dye 2-[2-(5-carboxy)oxazole]-5-hydroxy-6-aminobenzofuran-N,N,O-triacetic-acid
(FURAPTRA) on exuded sieve-tube sap. Although the sap interfered severely with the fluorescence properties of the dye, Ca2+ titrations enabled a value of [Ca2+]p = 20 μM to be deduced. The third method used Ca2+-selective microelectrodes on exuded sap samples, which gave an average value for [Ca2+]p = 13 μM. No significant change in this value was observed during the sap exudation period. The Ca2+ buffer capacity was determined and the result of about 0.6 mmol · l−1 · pCa−1 displayed excellent agreement with the measured values of free and total Ca2+ concentration in sieve-tube sap. Since the measured values for free Ca2+ are 20- to 100-fold higher than those usually reported for the cytosol of a range of plant cells in resting conditions, it
is concluded that either regulation of [Ca2+]p is of limited physiological importance, or that the Ca2+-dependent proteins respond only to relatively high [Ca2+]p. The implications for regulation of cytosolic free Ca2+ in symplastically connected companion cells is discussed.
Received: 15 February 1998 / Accepted: 14 March 1998 相似文献
4.
Bhaskar Bhadra Ashis Kumar Nanda Ranadhir Chakraborty 《World journal of microbiology & biotechnology》2006,22(3):225-232
Summary A gram negative, motile, short rod-shaped, and nickel resistant (tolerating 6.5 mM Ni2+) bacterium, strain BB1A, was isolated from the waters of the River Torsa in Hashimara, Jalpaiguri district, West Bengal,
India. The isolate BB1A was identified as a strain of Acinetobacter junii following detailed analysis of morphological, physio-biochemical and 16S rRNA gene sequence. The expression of nickel resistance
in BB1A was inducible by exposure to nickel chloride at a concentration as low as 50 μM Ni2+. The other metal ions, Cu2+, Zn2+, or Pb2+ at a concentration range of 20–30 μM, also induced the nickel resistance system in this bacterium. Southern hybridizations
of BB1A genomic DNA with digoxigenin-dUTP labeled DNA probes specific for well known nickel resistance determinants, cnr, ncc or nre, resulted in no detectable signal, but nir specific probe yielded weak hybridization signal with restricted genomic DNA of BB1A. The isolate BB1A, therefore, carries
out a novel induction phenomenon of nickel resistance and presumably with a nickel resistance genetic system different from
that previously characterized in other bacteria. 相似文献
5.
Borisova T Krisanova N Sivko R Kasatkina L Borysov A Griffin S Wireman M 《Neurochemistry international》2011,59(2):272-279
Exposure to Cd2+ and Pb2+ has neurotoxic consequences for human health and may cause neurodegeneration. The study focused on the analysis of the presynaptic mechanisms underlying the neurotoxic effects of non-essential heavy metals Cd2+ and Pb2+. It was shown that the preincubation of rat brain nerve terminals with Cd2+ (200 μM) or Pb2+ (200 μM) resulted in the attenuation of synaptic vesicles acidification, which was assessed by the steady state level of the fluorescence of pH-sensitive dye acridine orange. A decrease in l-[14C]glutamate accumulation in digitonin-permeabilized synaptosomes after the addition of the metals, which reflected lowered l-[14C]glutamate accumulation by synaptic vesicles inside of synaptosomes, may be considered in the support of the above data. Using isolated rat brain synaptic vesicles, it was found that 50 μM Cd2+ or Pb2+ caused dissipation of their proton gradient, whereas the application of essential heavy metal Mn2+ did not do it within the range of the concentration of 50-500 μM. Thus, synaptic malfunction associated with the influence of Cd2+ and Pb2+ may result from partial dissipation of the synaptic vesicle proton gradient that leads to: (1) a decrease in stimulated exocytosis, which is associated not only with the blockage of voltage-gated Ca2+ channels, but also with incomplete filling of synaptic vesicles; (2) an attenuation of Na+-dependent glutamate uptake. 相似文献
6.
T. C. Cox 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1999,169(4-5):344-350
Ion transport measured as short circuit current (Isc) across the skin of larval frogs is activated by amiloride, acetylcholine,
and ATP. In many epithelia, ATP stimulation of Isc involves an increase in intracellular calcium. To define the role of changes
in intracellular calcium in ATP stimulation of Isc in larval frog skin, epithelial cells were loaded with calcium by adding
5 μM ionomycin to a 2 mM calcium apical Ringer's solution. Calcium loading had no observable effect on baseline Isc or on
stimulation by ATP. Minimizing changes in intracellular calcium by loading the cell with the calcium chelator BAPTA also had
no measurable effect on ATP stimulation of Isc. When the apical side was bathed with Ca2+-free Ringer's solution, ionomycin increased Isc up to 15 μA. This increase was partially blocked by 2 mM Ca2+, 2 mM Mg2+, and 10 μM W-7. Other experiments showed that baseline-stimulated and ATP-stimulated Isc were always larger in 2 mM Mg2+ Ringer's compared to 2 mM Ca2+. In dissociated cells bathed in 2 mM Ca2+ Ringer's, ATP had no effect on intracellular calcium as measured by Fluo-LR fluorescence changes. In conclusion, ATP apparently
stimulates Isc without concomitant changes in intracellular calcium. This is consistent with a directly ligand-gated receptor
at the apical membrane with P2X-like characteristics.
Accepted: 21 April 1999 相似文献
7.
P. J. O'Brien 《Molecular and cellular biochemistry》1990,94(2):113-119
This study demonstrates a simple, rapid, and reproducible microassay for real-time monitoring of Ca2+-sequestration by isolated sarcoplasmic reticulum (SR) using ratiometric dual-emission spectrofluorometry and the fluorescent calcium-binding dye indo-1. The SR membranes were isolated by differential centrifugation and suspended in a medium including Ca2+, indo-1, ATP and oxalate. As Ca2+ was sequestered by SR, Ca2+-bound indo-1 fluorescence decreased equivalently but reciprocally to the increase in Ca2+ -free indo-1 fluorescence. The kinetic and thermodynamic properties of Ca2+-transport measured fluorometrically were similar to those measured radiometrically by 45Ca2+, with the exception that the former monitors changes in free Ca2+ whereas the latter monitors total Ca2+. An estimate of the maximal rate of change in total Ca2+ could be made by multiplying the maximal rate of change in free Ca2+ by the ratio of initial total Ca2– to free Ca2– concentration. 相似文献
8.
Lead (Pb) is a trace metal element in the human body. In order to understand the hazard mechanism of the elevated blood lead
level on the human body, the effect of Pb2+ on the human ether-à-go-go-related gene (hERG) K+ channel in the HEK 293 cell was investigated for the first time using whole-cell patch clamp technique, molecular dynamics
simulation, and quantum chemistry calculation methods. We found that Pb2+ obviously inhibits the current of the hERG K+ channel, and delays the “activation” and “deactivation” of the hERG K+ channel, indicating that Pb2+ evidently decreases the function of the K+ channel in the cell. The effect is increased with increasing the concentration of Pb2+. When the concentration of Pb2+ is 400 μg L−1, the function of the K+ channel is entirely lost. The results from the molecular dynamics simulation and quantum chemistry calculation indicated
that Pb2+ can coordinate with the oxygen/sulfur atoms in the K+ channel protein, leading to the decrease in the function of the K+ channel. According to the experimental results, we suggested that once the K+ channel in the human body was irreversibly inactivated by Pb2+, it would affect the treatment and prognosis of Pb2+ intoxication. 相似文献
9.
Zhiliang Jiang Yanyan Fan Aihui Liang Guiqing Wen Qingye Liu Tingsheng Li 《Plasmonics (Norwell, Mass.)》2010,5(4):375-381
The resonance scattering spectral probe for Pb2+ was obtained using aptamer-modified AuPd Nanoalloy. In the pH 7.0 Na2HPO4–NaH2PO4 buffer solution, the aptamer interacted with AuPd nanoalloy particles to form stable aptamer-AuPd nanoalloy probe for Pb2+ that is stable in high concentration of salt. The probe combined with Pb2+ ions to form a G-quadruplex and to release AuPd nanoalloy particles that aggregate to form big particles which led the resonance
scattering (RS) intensity enhancing. The reaction solution was filtered by 0.15 μm membrane to obtain the filtration containing
aptamer-AuPd nanoalloy probe that has strong catalytic effect on the electrodeless nickel particle plating reaction between
Ni(II) and PO23− that exhibited a strong RS peak at 508 nm. The RS intensity at 508 nm decreased when the Pb2+ concentration increased. The decreased intensity (ΔI
508nm) is linear to the concentration of 0.08–42 nM Pb2+, with regress equation of DI508nm = 16.3 c + 1.5 \Delta {I_{{5}0{\rm{8nm}}}} = {16}.{3}\,c + {1}.{5} , correlation coefficient of 0.9965, and detection limit of 0.04 nM Pb2+. The RS assay was applied to the analysis of Pb2+ in wastewater, with satisfactory results. 相似文献
10.
ATP-dependent Sr2+ transport was examined in vitro using basolateral membrane (BLM) vesicles isolated from rat renal cortex to clarify the discrimination
mechanisms between strontium (Sr) and calcium (Ca) in renal tubules during reabsorption. ATP-dependent Sr2+ uptake and Ca2+ uptake were observed in renal BLM vesicles and were inhibited by vanadate. Hill plots indicate similar kinetic behavior for
Ca2+ and Sr2+ uptake. The apparentK
m andV
max of ATP-dependent Sr2+ uptake were both higher than those for Ca2+ uptake. ATP-dependent Sr2+ uptake by BLM vesicles diminished in the presence of 0.1 μM Ca2+ and was more markedly inhibited by 1 μM Ca2+. Hill plots of Sr2+ uptake data with and without 0.1 μM Ca2+ showed that the cooperative behavior of Sr2+ uptake was not changed by Ca2+. In the presence of 0.1 μM Ca2+, the affinity of the transport system for Sr2+ and the velocity of Sr2+ uptake in the BLM were both decreased. However, the rate of Ca2+ uptake was not diminished by Sr2+ concentrations of <1.6 μM. These results suggest that Ca2+ is preferentially transported in the renal cortex BLM when Ca2+ and Sr2+ are present at the same time. 相似文献
11.
The permeability of biological membranes to boric acid was investigated using the giant internodal cells of the charophyte
alga Chara corallina (Klein ex Will. Esk. R.D. Wood). The advantage of this system is that it is possible to distinguish between membrane transport
of boron (B) and complexing of B by plant cell walls. Influx of B was found to be rapid, with equilibrium between the intracellular
and extracellular phases being established after approximately 24 h when the external concentration was 50 μM. The intracellular
concentration at equilibrium was 55 μM, which is consistent with passive distribution of B across the membrane along with
a small amount of internal complexation. Efflux of B occurred with a similar half-time to influx, approximately 3 h, which
indicates that the intracellular B was not tightly complexed. The concentration dependence of short-term influx measured with
10B-enriched boric acid was biphasic. This was tentatively attributed to the operation of two separate transport systems, a
facilitated system that saturates at 5 μM, and a linear component due to simple diffusion of B through the membrane. V
max and K
m for the facilitated transport system were 135 pmol m−2 s−1 and 2 μM, respectively. The permeability coefficient for boric acid in the Chara plasmalemma estimated from the slope of the linear influx component was 4.4 × 10−7 cm s−1 which is an order of magnitude lower than computed from the ether:water partition coefficient for B.
Received: 14 August 2000 / Accepted: 16 September 2000 相似文献
12.
Aldo Viarengo Graziella Mancinelli Bruno Burlando Isabella Panfoli Barbara Marchi 《Polar Biology》1999,21(6):369-375
Cell calcium is accumulated in intracellular stores by sarco-endoplasmic reticulum Ca2+ ATPases functionally interacting with the membrane lipid environment. Cold adaptations of membrane lipids in Antarctic Sea
organisms suggest possible adaptive effects also on sarco-endoplasmic reticulum Ca2+ ATPases. We investigated the SR Ca2+ ATPase of an Antarctic scallop, Adamussium colbecki, by characterising the enzyme activity and studying temperature effects. Ca2+ ATPase, assayed by following ATP hydrolysis, was thapsigargin- and vanadate-sensitive, showed maximum activity under 2 μM
Ca2+, 200 mM KCl and pH 7.2, and had a K
M for ATP of 22 ± 7 μM. Temperature effects showed an Arrhenius inversion between −1.8 and 0°C, indicating cold adaptation,
an Arrhenius break at 10°C, and a collapse above 20°C. A. colbecki accumulates high amounts of cadmium in the digestive gland; heavy metal effects on sarco-endoplasmic reticulum Ca2+ ATPases were therefore tested, finding an IC50 = 0.9 μM for Hg2+ and 3 μM for Cd2+. Finally, SDS-PAGE analysis showed a main band at about 100 kDa, which was identified as sarco-endoplasmic reticulum Ca2+ ATPase after trypsin digestion, and accounted for 60% total protein.
Accepted: 10 December 1998 相似文献
13.
Sylwia Pawlak Anna Firych Katarzyna Rymer Joanna Deckert 《Acta Physiologiae Plantarum》2009,31(4):741-747
The cadmium (Cd2+) and lead (Pb2+)-induced changes in Cu,Zn-SOD gene expression on the level of mRNA accumulation and enzyme activity were analyzed in roots of soybean (Glycine
max) seedlings. The Cd2+ caused the induction of copper–zinc superoxide dismutase (Cu,Zn-SOD) mRNA accumulation, at each analyzed metal concentration
(5–25 mg/l), whereas in Pb2+-treated roots this effect was observed only at the medium metal concentrations (50–100 mg/l of Pb2+). The analysis of Cu,Zn-SOD activity proved an increase in enzyme activity during Cd2+/Pb2+ stresses, however in Pb2+-treated plants the activity of enzyme was not correlated with respective mRNAs level. Presented data suggest that different
metals may act on various level of Cu,Zn-SOD expression in plants exposed to heavy metals stress. 相似文献
14.
Boron (B) is a developmental and reproductive toxin. It is also essential for some organisms. Plants use uptake and efflux
transport proteins to maintain homeostasis, and in humans, boron has been reported to reduce prostate cancer. Ca2+ signaling is one of the primary mechanisms used by cells to respond to their environment. In this paper, we report that boric
acid (BA) inhibits NAD+ and NADP+ as well as mechanically induced release of stored Ca2+ in growing DU-145 prostate cancer cells. Cell proliferation was inhibited by 30% at 100μM, 60% at 250μM, and 97% at 1,000μM
BA. NAD+-induced Ca2+ transients were partly inhibited at 250μM BA and completely at 1,000μM BA, whereas both NADP+ and mechanically induced transients were inhibited by 1,000μM BA. Expression of CD38 protein increased in proportion to BA
exposure (0–1,000μM). In vitro mass spectrometry analysis showed that BA formed adducts with the CD38 products and Ca2+ channel agonists cyclic adenosine diphosphate ribose (cADPR) and nicotinic acid adenine dinucleotide phosphate (NAADP). Vesicles
positive for the Ca2+ fluorophore fluo-3 acetoxymethyl ester accumulated in cells exposed to 250 and 1,000μM BA. The BA analog, methylboronic acid
(MBA; 250 and 1,000μM), did not inhibit cell proliferation or NAD+, NADP+, or mechanically stimulated Ca2+ store release. Nor did MBA increase CD38 expression or cause the formation of intracellular vesicles. Thus, mammalian cells
can distinguish between BA and its synthetic analog MBA and exhibit graded concentration-dependent responses. Based on these
observations, we hypothesize that toxicity of BA stems from the ability of high concentrations to impair Ca2+ signaling. 相似文献
15.
The effect of heavy metal cations on the mitochondrial ornithine/citrulline transporter was tested in proteoliposomes reconstituted
with the protein purified from rat liver. The transport activity was measured as [3H]ornithine uptake in proteoliposomes containing internal ornithine (ornithine/ornithine antiport mode) or as [3H]ornithine efflux in the absence of external substrate (ornithine/H+ transport mode). 0.1 mM Cu2+, Pb2+, Hg2+, Cd2+ and Zn2+ strongly inhibited (more than 85%) the antiport; whereas Mn2+, Co2+ and Ni2+ inhibited less efficiently (25, 47 and 69%, respectively). The IC50 values of the transporter for the different metal ions ranged from 0.71 to 350 μM. Co2+ and Ni2+ also inhibited the [3H]ornithine efflux whereas Cu2+, Pb2+, Hg2+, Cd2+ and Zn2+ stimulated the [3H]ornithine efflux. The stimulation of the [3H]ornithine efflux by Cu2+ and Cd2+ (as well as by Pb2+, Hg2+ and Zn2+) was not prevented by NEM and was reversed by DTE. These features indicated that the inhibition of the antiport was due to
the interaction of the Cu2+, Pb2+, Hg2+, Cd2+ and Zn2+ with a population of SH groups, of the transporter, responsible for the inhibition of the physiological function; whereas
the stimulation of [3H]ornithine efflux was due to the induction of a pore-like function of the transporter caused by interaction of cations with
a different population of SH groups. Differently, the inhibition of the ornithine transporter by Ni2+, Co2+ or Mn2+ was caused by interaction with the substrate binding site, as indicated by the competitive or mixed inhibition. 相似文献
16.
The steady-state levels of Ca2+ within the endoplasmic reticulum (ER) and the transport of 45Ca2+ into isolated ER of barley (Hordeum vulgare L. cv. Himalaya) aleurone layers were studied. The Ca2+-sensitive dye indo-1. Endoplasmic reticulum was isolated and purified from indo-1-loaded protoplasts, and the Ca2+ level in the ER was measured using the Ca2+-sensitive dye indo-1. Endoplasmic reticulum was isolated and purified from indo-1-loaded protoplasts, and the Ca2+ level in the lumen of the ER was determined by the fluorescence-ratio method to be at least 3 M. Transport of 45Ca2+ into the ER was studied in microsomal fractions isolated from aleurone layers incubated in the presence and absence of gibberellic acid (GA3) and Ca2+. Isopycinic sucrose density gradient centrifugation of microsomal fractions isolated from aleurone layers or protoplasts separates ER from tonoplast and plasma membranes but not from the Golgi apparatus. Transport of 45Ca2+ occurs primarily in the microsomal fraction enriched in ER and Golgi. Using monensin and heat-shock treatments to discriminate between uptake into the ER and Golgi, we established that 45Ca2+ transport was into the ER. The sensitivity of 45Ca2+ transport to inhibitors and the Km of 45Ca2+ uptake for ATP and Ca2+ transport in the microsomal fraction of barley aleurone cells. The rate of 45Ca2+ transport is stimulated several-fold by treatment with GA3. This effect of GA3 is mediated principally by an effect on the activity of the Ca2+ transporter rather than on the amount of ER.Abbreviations CCR
cytochrome-c reductase
- DCCD
dicyclohexylcarbodiimide
- EGTA
ethylene glycol bis(-aminoethyl ether)-N,N,N,N-tetraacetic acid
- ER
endoplasmic reticulum
- FCCP
carbonylcyanide p-trifluoromethoxyphenyl hydrazone
- GA3
gibberellic acid
- IDPase
inosine diphosphatase
- Mon
monensin 相似文献
17.
Alpana Singh S. K. Mehta J. P. Gaur 《World journal of microbiology & biotechnology》2007,23(8):1115-1120
Non-living (dried) biomass of five common filamentous algae belonging to Chlorophyta and Cyanophyta (Cyanobacteria) were screened
for their metal ion sorption and removal efficiency in a batch system. A considerably higher magnitude of sorption of Pb2+ and Cu2+ by all the tested algae suggests the prevalence of Pb2+- and Cu2+-binding ligands in them. The Langmuir isotherm could more appropriately describe metal sorption by the test algae than the
Freundlich isotherm. A 1 g l−1 biomass concentration of Pithophora odeogonia and Spirogyra neglecta, respectively removed 97 and 89% Pb2+in 30 min from a solution containing 5 mg l−1 initial concentration of Pb2+. Metal ion removal by the test algae decreased with increase in metal concentration in the solution. S. neglecta could remove >70% Pb2+ even from a solution containing 75 mg Pb2+ l−1. S. neglecta and P. oedogonia could remove more than 75% of Pb2+ and Cu2+ from a multi-metal solution, and therefore have tremendous potential for removing Pb2+and Cu2+ from wastewaters containing several metal ions simultaneously. Other test algae, namely, Hydrodictyon reticulatum, Cladophora calliceima and Aulosira fertilissima were relatively less efficient in removing metal ions from solution. 相似文献
18.
M. Oortgiesen R. G. D. M. van Kleef H. P. M. Vijverberg 《The Journal of membrane biology》1990,113(3):261-268
Summary Superfusion with Pb2+ induces a slow, noninactivating and reversible inward current in voltage-clamped N1E-115 neuroblastoma cells. The amplitude of this inward current increases in the range of 1–200 m Pb2+. Single-channel patch-clamp experiments have revealed that this inward current is mediated by discrete ion channels. Reversal potentials from linearI–V relationships are close to 0 mV for whole-cell and single-channel currents and the single-channel conductance amounts to 24 pS. The Pb2+-induced membrane current is not mediated by various known types of ion channels, since it is not blocked by external tetrodotoxin, tetraethylammonium,d-tubocurarine, atropine, ICS 205-930 and by internal EGTA. In Na+-free solutions superfusion with Pb2+ neither evokes a whole-cell inward current, nor single-channel openings. At –80 mV the open-time distribution of the single channels activated by 1m Pb2+ is dual exponential with time constants of 17 and 194 msec. When the Pb2+ concentration is increased from 1 to 20 m these time constants decrease to 2 and 13 msec, but the amplitude of single-channel currents remains –1.9 nA. Cd2+ and Al3+ induce inward currents and single-channel openings similar to Pb2+. Time constants fitted to the open-time distribution of single channels are 14 and 135 msec in the presence of 1 m Cd2+ and 15 and 99 msec in the presence of 50 m Al3+. Conversely, Cu2+ induces an irreversible inward current in neuroblastoma cells. Single-channel openings are undetected in the presence of Cu2+ and in Na+-free solutions Cu2+ is still able to induce an inward current. It is concluded that Pb2+, Cd2+ and possibly Al3+ activate a novel type of metal ionactivated (MIA) channel in N1E-115 cells. 相似文献
19.
In this study, we evaluated how cadmium inhibitory effect on photosystem II and I electron transport may affect light energy
conversion into electron transport by photosystem II. To induce cadmium effect on the photosynthetic apparatus, we exposed
Chlamydomonas reinhardtii 24 h to 0–4.62 μM Cd2+. By evaluating the half time of fluorescence transients O–J–I–P at different temperatures (20–30°C), we were able to determine
the photosystem II apparent activation energies for different reduction steps of photosystem II, indicated by the O–J–I–P
fluorescence transients. The decrease of the apparent activation energies for PSII electron transport was found to be strongly
related to the cadmium-induced inhibition of photosynthetic electron transport. We found a strong correlation between the
photosystem II apparent activation energies and photosystem II oxygen evolution rate and photosystem I activity. Different
levels of cadmium inhibition at photosystem II water-splitting system and photosystem I activity showed that photosystem II
apparent activation energies are strongly dependent to photosystem II donor and acceptor sides. Therefore, the oxido-reduction
state of whole photosystem II and I electron transport chain affects the conversion of light energy from antenna complex to
photosystem II electron transport. 相似文献
20.
S Silver 《Journal of industrial microbiology & biotechnology》1998,20(1):1-12
Bacterial chromosomes have genes for transport proteins for inorganic nutrient cations and oxyanions, such as NH4
+, K+, Mg2+, Co2+, Fe3+, Mn2+, Zn2+ and other trace cations, PO4
3-, SO4
2- and less abundant oxyanions. Together these account for perhaps a few hundred genes in many bacteria. Bacterial plasmids
encode resistance systems for toxic metal and metalloid ions including Ag+ AsO2
-, AsO4
3-, Cd2+, Co2+, CrO4
2−, Cu2+, Hg2+, Ni2+, Pb2+, TeO3
2−, TI+ and Zn2+. Most resistance systems function by energy-dependent efflux of toxic ions. A few involve enzymatic (mostly redox) transformations.
Some of the efflux resistance systems are ATPases and others are chemiosmotic ion/proton exchangers. The Cd2+-resistance cation pump of Gram-positive bacteria is membrane P-type ATPase, which has been labeled with 32P from [γ-32P]ATP and drives ATP-dependent Cd2+ (and Zn2+) transport by membrane vesicles. The genes defective in the human hereditary diseases of copper metabolism, Menkes syndrome
and Wilson’s disease, encode P-type ATPases that are similar to bacterial cadmium ATPases. The arsenic resistance system transports
arsenite [As(III)], alternatively with the ArsB polypeptide functioning as a chemiosmotic efflux transporter or with two polypeptides,
ArsB and ArsA, functioning as an ATPase. The third protein of the arsenic resistance system is an enzyme that reduces intracellular
arsenate [As(V)] to arsenite [As(III)], the substrate of the efflux system. In Gram-negative cells, a three polypeptide complex
functions as a chemiosmotic cation/protein exchanger to efflux Cd2+, Zn2+ and Co2+. This pump consists of an inner membrane (CzcA), an outer membrane (CzcC) and a membrane-spanning (CzcB) protein that function
together.
Received 08 August 1997/ Accepted in revised form 01 November 1997 相似文献