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1.
The absorption characteristics of Cd 2+ by 10- to 12-day-old soybean plants ( Glycine max cv Williams) were investigated with respect to influence of Cd concentration on adsorption to root surfaces, root absorption, transport kinetics and interaction with the nutrient cations Cu 2+, Fe 2+, Mn 2+, and Zn 2+. The fraction of nonexchangeable Cd bound to roots remained relatively constant at 20 to 25% of the absorbed fraction at solution concentration of 0.0025 to 0.5 micromolar, and increased to 45% at solution concentration in excess of 0.5 micromolar. The exchangeable fraction represented 1.4 to 32% of the absorbed fraction, and was concentration dependent. Using dinitrophenol as a metabolic inhibitor, the `metabolically absorbed' fraction was shown to represent 75 to 80% of the absorbed fraction at concentration less than 0.5 micromolar, and decreased to 55% at 5 micromolar. At comparatively low Cd concentrations, 0.0025 to micromolar 0.3, root absorption exhibited two isotherms with K2 values of 0.08 and 1.2 micromolar. Root absorption and transfer from root to shoot of Cd 2+ was inhibited by Cu 2+, Fe 2+, Mn 2+, and Zn 2+. Analyses of kinetic interaction of these nutrient cations with Cd 2+ indicated that Cu 2+, Fe 2+, Zn 2+, and possibly Mn 2+ inhibited Cd absorption competitively suggesting an involvement of a common transport site or process. 相似文献
2.
Effects of Cu 2+ on a non-specific conductance and H +-ATPase activity in the plasma membrane of the freshwater alga Nitella flexilis L. Agardh was studied using a conventional microelectrode voltage-clamp technique. We show that a Cu 2+-induced increase in the non-specific conductance is related to the formation of pores in the plasma membrane. Pore formation
is the result of unidentified chemical reactions, since the Q 10 for the rate of increase of conductance over time was about 3. Various oxidants and antioxidants (10 mmol/l H 2O 2, 10 mmol/l ascorbate, 100 μg/ml superoxide dismutase, and 100 μg/ml catalase) did not alter Cu 2+-induced changes in the plasma membrane conductance, suggesting that the effect of Cu 2+ was unrelated to peroxidation of plasma-membrane lipids. In contrast, organic and inorganic Ca 2+-channel antagonists (nifedipine, Zn 2+, Cd 2+, Fe 2+, Ni 2+) inhibited the Cu 2+-induced non-specific conductance increase. This suggests that changes in Ca 2+ influx underlie this effect of Cu 2+. Decreasing the pH or the ionic strength of external solutions also inhibited the Cu 2+-induced plasma-membrane conductance increase. Copper was also found to inhibit plasma-membrane H +-ATPase activity with half-maximal inhibition occurring at about 5–20 μmol/l and full inhibition at about 100–300 μmol/l.
The Hill coefficient of Cu 2+ inhibition of the H +-ATPase was close to two.
Received: 8 December 1999 / Accepted: 16 August 2000 相似文献
3.
1. Heavy metals (Hg 2+, Cu 2+, Cd 2+, Zn 2+, Pb 2+) at micromolar concentrations strongly inhibit the Ca 2+-ATPase activity present in the plasma-membrane obtained from the gill cells of Mytilus galloprovincialis Lam. Heavy metals act through inhibition of the formation of the phosphorylated intermediate.2. All the heavy metals tested inhibit the Ca 2+-ATPase activity, the effect following the order: Hg 2+ > Pb 2+ > Cu 2+ > Cd 2+ > Zn 2+; the simultaneous addition of different heavy metals causes a summatory inhibition of the enzyme activity; addition to the reaction mixture of GSH at a final concentration of 0.5 mM, reverses inhibitory effects of heavy metals.3. The inhibitory effects of Cu 2+ on Ca 2+-ATPase are highly enhanced by addition of ascorbate to the reaction mixture. In the presence of ascorbate (100 μM), copper strongly stimulates the lipid peroxidation damage of the gill plasma-membranes, a result that may explain the high copper cytotoxicity. 相似文献
4.
Prokaryotic enzymes formamidopyrimidine-DNA glycosylase (Fpg) and endonuclease VIII (Nei) and their eukaryotic homologs NEIL1,
NEIL2, and NEIL3 define the Fpg family of DNA glycosylases, which initiate the process of repair of oxidized DNA bases. The
repair of oxidative DNA lesions is known to be impaired in vivo in the presence of ions of some heavy metals. We have studied the effect of salts of several alkaline earth and transition
metals on the activity of Fpg-family DNA glycosylases in the reaction of excision of 5,6-dihydrouracil, a typical DNA oxidation
product. The reaction catalyzed by NEIL1 was characterized by values K
m = 150 nM and k
cat = 1.2 min −1, which were in the range of these constants for excision of other damaged bases by this enzyme. NEIL1 was inhibited by Al 3+, Ni 2+, Co 2+, Cd 2+, Cu 2+, Zn 2+, and Fe 2+ in Tris-HCl buffer and by Cd 2+, Zn 2+, Cu 2+, and Fe 2+ in potassium phosphate buffer. Fpg and Nei, the prokaryotic homologs of NEIL1, were inhibited by the same metal ions as NEIL1.
The values of I 50 for NEIL1 inhibition were 7 μM for Cd 2+, 16 μM for Zn 2+, and 400 μM for Cu 2+. The inhibition of NEIL1 by Cd 2+, Zn 2+, and Cu 2+ was at least partly due to the formation of metal-DNA complexes. In the case of Cd 2+ and Cu 2+, which preferentially bind to DNA bases rather than phosphates, the presence of metal ions caused the enzyme to lose the
ability for preferential binding to damaged DNA. Therefore, the inhibition of NEIL1 activity in removal of oxidative lesions
by heavy metal ions may be a reason for their comutagenicity under oxidative stress. 相似文献
5.
It is well known that the principal biomolecules involved in Alzheimer’s disease (AD) are acetylcholinesterase (AChE), acetylcholine (ACh) and the amyloid beta peptide of 42 amino acid residues (Aβ42). ACh plays an important role in human memory and learning, but it is susceptible to hydrolysis by AChE, while the aggregation of Aβ42 forms oligomers and fibrils, which form senile plaques in the brain. The Aβ42 oligomers are able to produce hydrogen peroxide (H 2O 2), which reacts with metals (Fe 2+, Cu 2+, Cr 3+, Zn 2+, and Cd 2+) present at high concentrations in the brain of AD patients, generating the hydroxyl radical ( ·OH) via Fenton (FR) and Fenton-like (FLR) reactions. This mechanism generates high levels of free radicals and, hence, oxidative stress, which has been correlated with the generation and progression of AD. Therefore, we have studied in vitro how AChE catalytic activity and ACh levels are affected by the presence of metals (Fe 3+, Cu 2+, Cr 3+, Zn 2+, and Cd 2+), H 2O 2 (without Aβ42), and · OH radicals produced from FR and FLR. The results showed that the H 2O 2 and the metals do not modify the AChE catalytic activity, but the ·OH radical causes a decrease in it. On the other hand, metals, H 2O 2 and ·OH radicals, increase the ACh hydrolysis. This finding suggests that when H 2O 2, the metals and the ·OH radicals are present, both, the AChE catalytic activity and ACh levels diminish. Furthermore, in the future it may be interesting to study whether these effects are observed when H 2O 2 is produced directly from Aβ42. 相似文献
6.
A metallothionein-like gene, ThMT3, encoding a type 3 metallothionein, was isolated from a Tamarix hispida leaf cDNA library. Expression analysis revealed that mRNA of ThMT3 was upregulated by high salinity as well as by heavy metal ions, and that ThMT3 was predominantly expressed in the leaf. Transgenic yeast ( Saccharomyces cerevisiae) expressing ThMT3 showed increased tolerance to Cd 2+, Zn 2+, Cu 2+, and NaCl stress. Transgenic yeast also accumulated more Cd 2+, Zn 2+, and NaCl, but not Cu 2+. Analysis of the expression of four genes ( GLR1, GTT2, GSH1, and YCF1) that aid in transporting heavy metal (Cd 2+) from the cytoplasm to the vacuole demonstrated that none of these genes were induced under Cd 2+, Zn 2+, Cu 2+, and NaCl stress in ThMT3-transgenic yeast. H 2O 2 levels in transgenic yeast under such stress conditions were less than half those in control yeast under the same conditions.
Three antioxidant genes ( SOD1, CAT1, and GPX1) were specifically expressed under Cd 2+, Zn 2+, Cu 2+, and NaCl stress in the transgenic yeast. Cd 2+, Zn 2+, and Cu 2+ increased the expression levels of SOD1, CAT1, and GPX1, respectively, whereas NaCl induced the expression of SOD1 and GPX1. 相似文献
7.
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 Cu 2+, Pb 2+, Hg 2+, Cd 2+ and Zn 2+ strongly inhibited (more than 85%) the antiport; whereas Mn 2+, Co 2+ and Ni 2+ inhibited less efficiently (25, 47 and 69%, respectively). The IC 50 values of the transporter for the different metal ions ranged from 0.71 to 350 μM. Co 2+ and Ni 2+ also inhibited the [ 3H]ornithine efflux whereas Cu 2+, Pb 2+, Hg 2+, Cd 2+ and Zn 2+ stimulated the [ 3H]ornithine efflux. The stimulation of the [ 3H]ornithine efflux by Cu 2+ and Cd 2+ (as well as by Pb 2+, Hg 2+ and Zn 2+) 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 Cu 2+, Pb 2+, Hg 2+, Cd 2+ and Zn 2+ 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 Ni 2+, Co 2+ or Mn 2+ was caused by interaction with the substrate binding site, as indicated by the competitive or mixed inhibition. 相似文献
8.
The effects of some metal ions on amidolytic and fibrinogenolytic activities of highly purified human plasmin were investigated
in vitro. In the presence of Zn 2+, Cu 2+, Cd 2+, and Au + in the incubation mixture at the concentrations of 1×10 −5−1×10 −3
M, the anidolytic plasmin activity was strongly inhibited, whereas Ca 2+ and Mg 2+ at the same concentrations were not effective. The analysis of the kinetic study has shown that Zn 2+ or Cu 2+ acts as mixed-type inhibitors of plasmin activity. The inhibition of amidolytic plasmin activity by Zn 2+ and Cu 2+ was reduced in the presence of EDTA, histidine, or albumin. Incubation of plasmin with Zn 2+ or Cu 2+ (at the concentration of 5×10 −4
M) resulted in complete loss of its proteolytic action on fibrinogen, whereas Cd 2+ and Au + under the same conditions only partially inhibited this process. 相似文献
9.
At 10 mM, Cu + was highly protective against killing of spores of Bacillus megaterium ATCC 19213 by H 2O 2, while at higher concentrations, from 15–100 mM, killing was augmented. In contrast, Cu 2+, Fe 2+, Fe 3+, Co 2+ or Co 3+ ions acted only protectively. Cu + itself was sporicidal in the absence of H 2O 2 or ascorbate, and its sporicidal action did not depend on generation of highly reactive oxygen species. It appeared that
killing involved either inhibition of germination or copper toxicity to germinated cells in that Cu +-inactivated spores did not germinate readily but chemical decoating of the cells prior to plating on a solid medium resulted
in reversal of the sporicidal effect.
Received 12 July 1996/ Accepted in revised form 03 November 1996 相似文献
10.
Glutathione S‐transferases (GSTs) are the superfamily of multifunctional detoxification isoenzymes and play important role cellular signaling. The present article focuses on the role of Cd 2+, Cu 2+, Zn 2+, and Ag + in vitro inhibition of GST. For this purpose, GST was purified from Van Lake fish ( Chalcalburnus tarichii Pallas) gills with 110.664 EU mg ?1 specific activity and 79.6% yield using GSH‐agarose affinity chromatographic method. The metal ions were tested at various concentrations on in vitro GST activity. IC 50 values were found for Cd +2, Cu +2, Zn +2, Ag + as 450.32, 320.25, 1510.13, and 16.43 μM, respectively. K i constants were calculated as 197.05 ± 105.23, 333.10 ± 152.76, 1670.21 ± 665.43, and 0.433 ± 0.251 μM, respectively. Ag + showed better inhibitory effect compared with the other metal ions. The inhibition mechanisms of Cd 2+ and Cu 2+ were non‐competitive, whereas Zn 2+ and Ag + were competitive. Co 2+, Cr 2+, Pb 2+, and Fe 3+ had no inhibitory activity on GST. 相似文献
11.
In vitro exposure of human erythrocytes to H2O2 at concentrations of 30–1000 μM resulted in a dose-dependent increase of the intracellular levels of Zn2+ and inhibition of the cytosolic esterase activity, which is a major marker of erythrocyte viability. The observed effect depended on the concentration of H2O2 and the duration of exposure of the cells to this compound. An inverse relationship between the changes in the intracellular level of labile zinc ions and esterase activity in the cells exposed to hydrogen peroxide was detected; this was indicative of the role of Zn2+ in the programmed death of red blood cells. The combined action of hydrogen peroxide and N',N'-tetrakis-(2-pyridyl-methyl)-ethylenediamine, an intracellular zinc ion chelator, has been found to eliminate the cytotoxic effect of H2O2, whereas the addition of Zn2+ to the erythrocyte incubation medium enhanced the effects of hydrogen peroxide. The reduction of the concentration of non-protein thiol groups due to a decrease of the level of reduced glutathione was shown to contribute to the release of Zn2+ from the intracellular binding sites during oxidative stress induced by H2O2 in human erythrocytes. 相似文献
12.
该研究以Cu~(2+)、Zn~(2+)、Cd~(2+)单一胁迫为对照,探讨不同浓度的Cu~(2+)、Zn~(2+)、Cd~(2+)复合胁迫对麻疯树幼苗生理生化指标的影响。结果表明:随着Cu~(2+)、Zn~(2+)、Cd~(2+)浓度的增加,麻疯树幼苗叶片中的蛋白质(Pro)、丙二醛(MDA)含量均逐渐增加,其叶片叶绿素含量随着Zn~(2+)胁迫浓度的增加呈现出先降后升的趋势,在中等浓度(100 mg·L-1)的Zn~(2+)胁迫时含量最低、随着Cu~(2+)胁迫浓度的增加叶绿素含量先升高后降低,在Cu~(2+)浓度为200 mg·L-1时含量最高,达到1 200 mg·g-1FW; Cd~(2+)胁迫对叶绿素含量和根系活力无明显影响。根系活力在Zn~(2+)浓度为100 mg·L~(-1)时最强,随着Cu~(2+)浓度的增加而减弱。低浓度的Cu~(2+)、Zn~(2+)、Cd~(2+)对过氧化物酶活性和可溶性糖含量都具有促进作用。Cu~(2+)、Zn~(2+)、Cd~(2+)复合胁迫时对可溶性蛋白、叶绿素和丙二醛含量均无明显影响,随着复合胁迫时浓度的增加,可溶性糖含量和根系活力先增后减。这表明麻疯树对三种重金属的胁迫具有一定的抗性,过高浓度的胁迫会影响麻疯树幼苗生理生化的一些指标,但是麻疯树可以通过自身的防御系统使伤害降到最小。此外,重金属复合胁迫可以在一定程度上减轻单一胁迫对麻疯树幼苗造成的毒害作用。 相似文献
13.
The acute effects of aqueous solutions of As, Cd, Cu, Pb, F, and Zn ions at concentrations from 0.01 to 100 micrograms per milliliter and solutions adjusted to pH 2 to 6 with nitric or sulfuric acid were studied with respect to acetylene reduction, net photosynthesis, respiration rate, and chlorophyll content in Vernal alfalfa ( Medicago sativa L. cv. Vernal). The effects of the various treatments on acetylene reduction varied from no demonstrable effect by any concentration of F − and 42% inhibition by 100 micrograms Pb 2+ per milliliter, to 100% inhibition by 10 micrograms Cd 2+ per milliliter and 100 micrograms per milliliter As, Cu 2+, and Zn 2+ ions. Zn 2+ showed statistically significant inhibition of activity at 0.1 micrograms per milliliter. Acid treatments were not inhibitory above pH 2, at which pH nitric acid inhibited acetylene reduction activity more than did sulfuric acid. The inhibition of acetylene reduction by these ions was Zn 2+ > Cd 2+ > Cu 2+ > AsO 3− > Pb 2+ > F −. The sensitivity of acetylene reduction to the ions was roughly equal to the sensitivity of photosynthesis, respiration, and chlorophyll content when Pb 2+ was applied, but was 1,000 times more sensitive to Zn 2+. The relationship of the data to field conditions and industrial pollution is discussed. 相似文献
14.
The plasmalemma vesicles isolated from cucumber and maize roots were used to study the effect of Cu 2+ and Cd 2+ on the hydrolytic and proton pumping activities of ATPase. In vivo application of metal ions to the plant growth solutions resulted in stimulation of the proton transport in maize. In cucumber
roots the action of metals was not the same: cadmium stimulated the H + transport through plasmalemma whereas Cu 2+ almost completely inhibited it. Copper ions decreased the hydrolytic activity of H +-ATPase in cucumber, without any effect on this activity in membranes isolated from maize roots. The effect of cadmium on
the hydrolytic activities was opposite: ATP-hydrolysis activity in plasmalemma was not altered in cucumber, whereas in maize
its stimulation was observed. The amount of accumulated metals was not the main reason of different influence of metals on
H +-ATPase activity in tested plants. In in vitro experiments Cu 2+ inhibited H + transport in the cucumber, to a higher degree than Cd 2+ and both metals did not change this H +-ATPase activity of plasmalemma isolated from corn roots. Cu 2+ added into the incubation medium reduced the hydrolytic activity of ATPase in the plasma membrane isolated from cucumber
as well as from corn roots. Cd 2+ diminished the hydrolytic activity of ATPase in cucumber, and no effect of Cd 2+ in the plasmalemma isolated from corn roots was found. Our results indicated different in vitro and in vivo action of both metals on H +-ATPase and different response of this enzyme to Cu 2+ and Cd 2+ in maize and cucumber. 相似文献
15.
Heavy metals are common pollutants of the coastal saline area and Salicornia brachiata an extreme halophyte is frequently exposed to various abiotic stresses including heavy metals. The SbMT-2 gene was cloned and transformed to tobacco for the functional validation. Transgenic tobacco lines (L2, L4, L6 and L13) showed significantly enhanced salt (NaCl), osmotic (PEG) and metals (Zn ++, Cu ++ and Cd ++) tolerance compared to WT plants. Transgenic lines did not show any morphological variation and had enhanced growth parameters viz. shoot length, root length, fresh weight and dry weight. High seed germination percentage, chlorophyll content, relative water content, electrolytic leakage and membrane stability index confirmed that transgenic lines performed better under salt (NaCl), osmotic (PEG) and metals (Zn ++, Cu ++ and Cd ++) stress conditions compared to WT plants. Proline, H 2O 2 and lipid peroxidation (MDA) analyses suggested the role of SbMT-2 in cellular homeostasis and H 2O 2 detoxification. Furthermore in vivo localization of H 2O 2 and O 2
−; and elevated expression of key antioxidant enzyme encoding genes, SOD, POD and APX evident the possible role of SbMT-2 in ROS scavenging/detoxification mechanism. Transgenic lines showed accumulation of Cu ++ and Cd ++ in root while Zn ++ in stem under stress condition. Under control (unstressed) condition, Zn ++ was accumulated more in root but accumulation of Zn ++ in stem under stress condition suggested that SbMT-2 may involve in the selective translocation of Zn ++ from root to stem. This observation was further supported by the up-regulation of zinc transporter encoding genes NtZIP1 and NtHMA-A under metal ion stress condition. The study suggested that SbMT-2 modulates ROS scavenging and is a potential candidate to be used for phytoremediation and imparting stress tolerance. 相似文献
16.
The active site in bovine copper, zinc superoxide dismutase (Cu 2. Zn 2 SOD) has been studied by 111Cd time differential Perturbed Angular Correlation (PAC) on enzyme with Zn 2+ replaced by excited 'Cd 2+. The PAC spectra obtained for both the oxidized and the reduced form of Cu 2Cd 2SOD show no asymmetry between the two Zn-sites in the dimeric enzyme. The spectv further reveal that a significant change has taken place at the Zn-site in the reduced form compared to the oxidized form.Semi-empirical calculations based on the Angular Overlap Model (AOM) and coordinates from the crystal structure of the native enzyme are in agreement with the experimental PAC data of the oxidized enzyme. The results indicate that Cd 2+ coordinates in the same manner as Zn 2+ and that the crystal structure of SOD is valid for the enzyme in solution. The PAC spectrum of the reduced enzyme can be explained by extending the AOM calculations to the enzyme in the reduced form and assuming that the imidazol ring of His61 is no longer bridging the copper and cadmium ions in the reduced state. 相似文献
17.
The substrate requirement of the H +-ATPase in purified corn root tonoplast vesicles was investigated. The coupled activities, ATP hydrolysis and proton pumping, were simultaneously supported only by Mg 2+ or Mn 2+. The presence of Ca 2+ or Ba 2+ did not significantly affect the coupled activities. The addition of Cd 2+, Co 2+, Cu 2+, and Zn 2+ inhibited both the hydrolysis of Mg-ATP and the proton transport. However, the inhibition of proton pumping was more pronounced. Based on equilibrium analysis, both ATP-complexed and free forms of these cations were inhibitory. Inhibition of the hydrolysis of Mg-ATP could be correlated to the concentrations of the ATP-complex of Zn. On the other hand, the free Cu 2+ and Co 2+ were effective in inhibiting hydrolysis. For proton pumping, the ATP complexes of Co 2+, Cu 2+, and Zn 2+ were effective inhibitors. However, this inhibition could be further modulated by free Co 2+, Cu 2+, and Zn 2+. While the equilibrium concentrations of Cd-ATP and free Cd 2+ were not estimated, the total concentration of this cation needed to inhibit the coupled activities of the H +-ATPase was found to be in the range of 10 to 100 micromolars. The presence of free divalent cations also affected the structure of the lipid phase in tonoplast membrane as demonstrated by the changes of emission intensity and polarization of incorporated 1,6-diphenyl-1,3,5-hexatriene. The differential inhibition caused by these cations could be interpreted by interactions with the protogenic domain of the membrane as previously proposed in “indirect-link” mechanism. 相似文献
18.
In addition to the previously studied Zn 2+, low concentrations (about 0.5 mM) of Be 2+, Ba 2+, Cd 2+, Ni 2+, Cu 2+, Pt 4+ and, outstandingly, 0.5 µ M of UO 2
2+, potentiate the twitch of frog sartorius and toe muscles by prolonging the active state of contraction. The degree of potentiation is a roughly S-shaped function of p(metal 2+), suggesting that each metal binds to a ligand of the muscle fiber, representative apparent affinity constants being: UO 2
2+, 5 x 10 6; Zn 2+, 2.8 x 10 5; and Cd 2+, 2 x 10 4. UO 2
2+ potentiation effects are rapidly reversed by PO 4, and Zn 2+ and Cd 2+ effects by EDTA, PO 4, and cysteine. The rapidity of these reversals by the nonpenetrating EDTA and PO 4, and the fact that heavy metal ions evidently potentiate by prolonging the action potential, indicate that the metal potentiators exert their primary action at readily accessible (i.e. plasma and T tubular) membrane sites. The relatively slow kinetics of development of potentiation, and the even slower reversal of it in pure Ringer''s solution, indicate that the metal ions are bound to connective tissue, as well as to muscle fibers. The binding effects at the readily accessible membrane sites evidently impairs delayed rectification and thus modifies the action potential and excitation-contraction coupling so as to cause potentiation. SH is excluded, and PO 4 and imidazole are possibilities, as the membrane ligand binding the potentiating metal ions. 相似文献
19.
Hydrogen peroxide (H 2O 2)-induced aggregation of calf platelets and its modification by agents with specific properties were characterized employing
a spectrophotometric assay. An Arrhenius activation energy of 20 ± 1 kcal/mol was found in the temperature range of 25‡-36‡C.
Rate inhibition occurred on either side of this temperature range, and under anaerobic conditions. Exogenous Ca 2+ ions were not required but Ca 2+ ions, at 1 mM-concentration, optimally increased rates and extent of aggregation at suboptimal H 2O 2 concentrations but only extent of aggregation at optimal H 2O 2 concentrations. Ba 2+, Sr 2+, Cd 2+, Mn 2+ and Ni 2+ ions (1 mM) and Zn 2+, Pb 2+ and Hg 2+ ions (10 mM) were inhibitory. The cyclo-oxygenase inhibitor, indomethacin (10-30 mM) exerted only mild inhibition by a competitive
mechanism. Another cyclo-oxygenase inhibitor, aspirin, functioned to increase aggregation. Ligands acting directly at the
prostaglandin H 2/thromboxane A, receptor (5Z. 9, 11, 13E, 15(S) 15-hydroxy 9(11) epoxy methano prosta 5, 13-dien-1-oic acid, pinane thromboxane
A 2, arachidonic acid, eicosapentaenoic acid, and N-ethylmaleimide) functioned as competitive inhibitors. Another platelet-activating
sulphydryl reagent, thimerosal, also inhibited competitively while the protein kinase C inhibitor, sphingosine, and the protein
kinase C modulator, Zn 2+ ions, inhibited by different mechanisms. The results indicate direct action of H 2O 2 at the prostaglandin H 2/thromboxane A 2 receptor, possibly its sulphydryls, to activate the protein kinase C pathway, independently of cyclo-oxygenase products.
The results underscored the power of the kinetic approach for investigating mechanisms of platelet activation. 相似文献
20.
Previous work in our laboratory led to the isolation of a cadmium (Cd)-resistant variant (Cd r2C10) of the line CHO Chinese Hamster cell having a 10-fold greater resistance to the cytotoxic action of Cd 2+ compared with the CHO cell. This resistance was attributed to an increased capacity of the Cd 2+-resistant Cd r2C10 subline to induce synthesis of the Cd 2+- and Zn 2+-binding protein(s), metallothionein(s) (MT). Evidence that Cd 2+ behaves as an analog of the essential trace metal, Zn 2+, especially as an inducer of MT synthesis, suggested that the Cd r and CHO cell types could be employed to investigate cellular Zn 2+ metabolism. In the present study, measurements were made to compare CHO and Cd r cell types for (a) growth as a function of the level of ZnCl 2 added to the culture medium, (b) uptake and subcellular distribution of Zn 2+, and (c) capacity to induce MT synthesis. The results of these measurements indicated that (a) both CHO and Cd r cell types grew normally ( T
d≊16–18 h) during exposures to Zn 2+ at levels up to 100 μ M added to the growth medium, but displayed abrupt growth inhibition at higher Zn 2+ levels, (b) Cd r cells incorporate fourfold more Zn 2+ during a 24-h exposure to the maximal subtoxic level of Zn 2+ and (c) the CHO cell lacks the capacity to induce MT synethesis while the Cd r cell is proficient in this response during exposure to the maximal subtoxic Zn 2+ level. These findings suggest that (a) the CHO and Cd r cell systems will be useful in further studies of cellular Zn 2+ metabolism, especially in comparisons of Zn 2+ metabolism in the presence and absence of induction of the Zn 2+-sequestering MT and (b) a relationship exists between cellular capacity to induce MT synthesis and capacity for cellular
Zn 2+ uptake. 相似文献
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