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1.
Summary Redox inactivation of glutathione reductase involves metal cations, since chelators protected against NADPH-inactivation, 3 µM EDTA or 10 µM DETAPAC yielding full protection. Ag +, Zn 2+ and Cd 2+ potentiated the redox inactivation promoted by NADPH alone, while Cr 3+, Fe 2+, Fe 3+, Cu +, and Cu 2+ protected the enzyme. The Zn 2+ and Cd 2+ effect was time-dependent, unlike conventional inhibition. Glutathione reductase interconversion did not require dioxygen, excluding participation of active oxygen species produced by NADPH and metal cations. One Zn 2+ ion was required per enzyme subunit to yield full NADPH-inactivation, the enzyme being reactivated by EDTA. Redox inactivation of glutathione reductase could arise from the blocking of the dithiol formed at the active site of the reduced enzyme by metal cations, like Zn 2+ or Cd 2+.The glutathione reductase activity of yeast cell-free extracts was rapidly inactivated by low NADPH or moderate NADH concentrations; NADP + also promoted rapid inactivation in fresh extracts, probably after reduction to NADPH. Full inactivation was obtained in cell-free extracts incubated with glucose-6-phosphate or 6-phosphogluconate; the inactivating efficiency of several oxidizable substrates was directly proportional to the specific activities of the corresponding dehydrogenases, confirming that redox inactivation derives from NADPH formed in vitro.Abbreviations DETAPAC
diethylenetriaminepentaacetic acid
- 2,5-ADP-Sepharose-N 6-(6-aminohexyl) adenosine
2,5-bisphosphateSepharose 相似文献
2.
Essentially all bacteria have genes for toxic metal ion resistances and these include those for Ag+, AsO
−2
, AsO
3−4
, Cd2+, Co2+, CrO
2−4
, Cu2+, Hg2+, Ni2+, Pb2+, TeO
2−3
, Tl+ and Zn2+. The largest group of resistance systems functions by energy-dependent efflux of toxic ions. Fewer involve enzymatic transformations (oxidation, reduction, methylation, and demethylation) or metal-binding proteins (for example, metallothionein SmtA, chaperone CopZ and periplasmic silver binding protein SilE). Some of the efflux resistance systems are ATPases and others are chemiosmotic ion/proton exchangers. For example, Cd2+-efflux pumps of bacteria are either inner membrane P-type ATPases or three polypeptide RND chemiosmotic complexes consisting of an inner membrane pump, a periplasmic-bridging protein and an outer membrane channel. In addition to the best studied three-polypeptide chemiosmotic system, Czc (Cd2+, Zn2+, and Co2), others are known that efflux Ag+, Cu+, Ni2+, and Zn2+. Resistance to inorganic mercury, Hg2+ (and to organomercurials, such as CH3Hg+ and phenylmercury) involve a series of metal-binding and membrane transport proteins as well as the enzymes mercuric reductase and organomercurial lyase, which overall convert more toxic to less toxic forms. Arsenic resistance and metabolizing systems occur in three patterns, the widely-found ars operon that is present in most bacterial genomes and many plasmids, the more recently recognized arr genes for the periplasmic arsenate reductase that functions in anaerobic respiration as a terminal electron acceptor, and the aso genes for the periplasmic arsenite oxidase that functions as an initial electron donor in aerobic resistance to arsenite. 相似文献
3.
Zn 2+‐responsive repressor ZiaR and Co 2+‐responsive activator CoaR modulate production of P 1‐type Zn 2+‐ (ZiaA) and Co 2+‐ (CoaT) ATPases respectively. What dictates metal selectivity? We show that Δ ziaΔ coa double mutants had similar Zn 2+ resistance to Δ zia single mutants and similar Co 2+ resistance to Δ coa single mutants. Controlling either ziaA or coaT with opposing regulators restored no resistance to metals sensed by the regulators, but coincident replacement of the deduced cytosolic amino‐terminal domain CoaT N with ZiaA N (in ziaR‐ p ziaA‐ ziaANcoaT) conferred Zn 2+ resistance to Δ ziaΔ coa, Zn 2+ content was lowered and residual Co 2+ resistance lost. Metal‐dependent molar absorptivity under anaerobic conditions revealed that purified ZiaA N binds Co 2+ in a pseudotetrahedral two‐thiol site, and Co 2+ was displaced by Zn 2+. Thus, the amino‐terminal domain of ZiaA inverts the metals exported by zinc‐regulated CoaT from Co 2+ to Zn 2+, and this correlates simplistically with metal‐binding preferences; KZiaAN Zn 2+ tighter than Co 2+. However, Zn 2+ did not bleach Cu +‐ZiaA N, and only Cu + co‐migrated with ZiaA N after competitive binding versus Zn 2+. Bacterial two‐hybrid assays that detected interaction between the Cu +‐metallochaperone Atx1 and the amino‐terminal domain of Cu +‐transporter PacS N detected no interaction with the analogous, deduced, ferredoxin‐fold subdomain of ZiaA N. Provided that there is no freely exchangeable cytosolic Cu +, restricted contact with the Cu +‐metallochaperone can impose a barrier impairing the formation of otherwise favoured Cu +–ZiaA N complexes. 相似文献
4.
Summary The influence of different concentrations of the heavy metals cadmium (Cd 2+), cobalt (Co 2+), copper (Cu 2+), iron (Fe 2+ and Fe 3+), mercury (Hg 2+), manganese (Mn 2+), and zinc (Zn 2+), plus aluminium (Al 3+) (a toxic metal in polluted areas), on pollen germination and tube growth of Lilium longiflorum was investigated using light microscopy. Effects could be observed with 3 M and 100 M of heavy metal, added as chloride salts to the medium. Cd 2+, Cu 2+, and Hg 2+, showed the greatest toxicity, whereas germination and growth rate was less affected by Mn 2+. Affected tubes showed swelling of the tip region. Tubes treated with Cd 2+, Co 2+, Fe 2+, Fe 3+, Hg 2+, and Mn 2+ were also prepared for ultrastructural studies. In all cases, the main effect was abnormal cell wall organization, mostly at the tip, where round, fibrillar aggregates, the shape and size of secretory Golgi vesicles were formed. They built up a loose network which could be up to 10 m thick compared to untreated tubes where the cell wall was composed of thin layers of long fibrils and about 100 nm thick. Cd 2+ was the only metal which produced effects at the intracellular level: organelle distribution within the tip region appeared disorganized. A general mechanism of heavy metal action on pollen tube growth is discussed. 相似文献
5.
Acutolysin D, isolated from the venom of Agkistrodon acutus, possesses marked haemorrhagic and proteolytic activities. The molecular weight and the absorption coefficients ( A
1%
280) of acutolyisn D have been determined to be 47,850 ± 8 amu and 9.3 by mass spectrometer and UV spectrum, respectively. The effects of metal ions on the conformation and activity of acutolysin D have been studied by following fluorescence, circular dichroism and biological activity measurements. Acutolysin D contains two Ca 2+-binding sites and two Zn 2+-binding sites determined by atomic absorption spectrophotometer. Zn 2+ is essential for the enzyme activities of acutolysin D, however, the presence of 1 m M Zn 2+ significantly decreases its caseinolytic activity and intrinsic fluorescence intensity at pH 9.0 due to Zn(OH) 2 precipitate formation. Ca 2+ is important for the structural integrity of acutolysin D, and the presence of 1 m M Ca 2+ markedly enhances its caseinolytic activity. Interestingly, the caseinolytic activity which is inhibited partly by Cu 2+, Co 2+, Mn 2+ or Tb 3+ and inhibited completely by Cd 2+, is enhanced by Mg 2+. The fluorescence intensity of the protein decreases in the presence of Cu 2+, Co 2+, Cd 2+ or Mn 2+, but neither for Ca 2+, Mg 2+ nor for Tb 3+. Zn 2+, Ca 2+, Mg 2+, Cu 2+, Mn 2+, Co 2+ and Tb 3+ have slight effects on its secondary structure contents. In addition, Cd 2+ causes a marked increase of antiparallel β-sheet content from 45.5% to 60.2%. 相似文献
6.
The sialidase secreted by Clostridium chauvoei NC08596 was purified to apparent homogeneity by ion-exchange chromatography, gel filtration, hydrophobic interaction-chromatography, FPLC ion-exchange chromatography, and FPLC gel filtration. The enzyme was enriched about 10 200-fold, reaching a final specific activity of 24.4 U mg –1. It has a relatively high molecular mass of 300 kDa and consists of two subunits each of 150 kDa. The cations Mn 2+, Mg 2+, and Ca 2+ and bovine serum albumin have a positive effect on the sialidase activity, while Hg 2+, Cu 2+, and Zn 2+, chelating agents and salt decrease enzyme activity. The substrate specificity, kinetic data, and pH optimum of the enzyme are similar to those of other bacterial sialidases.Abbreviations FPLC
fast protein liquid chromatography
- NCTC
National Collection of Type Cultures
- ATCC
American Type Culture Collection
- MU-Neu5Ac
4-methylumbelliferyl-- d- N-acetylneuraminic acid
- buffer A
0.02 m piperazine, 0.01 m CaCl 2, pH 5.5
- buffer B
0.02 m piperazine, 0.01 m CaCl 2, 1.0 m NaCl, pH 5.5
- buffer C
0.1 m sodium acetate, 0.01 m CaCl 2, pH 5.5
- SDS
sodium dodecyl sulfate
- PAGE
polyacrylamide gel electrophoresis
- Neu5Ac
N-acetylneuraminic acid
- BSM
bovine submandibular gland mucin
- GD1a
IV 3Neu5Ac, II 3Neu5Ac-GgOse 4Cer
- GM1
II 3Neu5Ac-GgOse 4Cer
- MU-Neu4,5Ac 2
4-methylumbelliferyl-- d- N-acetyl-4- O-acetylneuraminic acid
- TLC
thin-layer chromatography
- HPTLC
high performance thin-layer chromatography
- EDTA
ethylenediamine tetraacetic acid
- EGTA
ethylene glycol bis(2-aminoethyl-ethen)- N,N,N,N-tetraacetic acid
- BSA
bovine serum albumin
- Neu5Ac2en
2-deoxy-2,3-didehydro- N-acetylneuraminic acid
- IEF
isoelectric focusing
- IEP
isoelectric point 相似文献
7.
Copper-induced metallothionein (MT) synthesis in Saccharomyces cerevisiae was investigated in order to associate this exclusively with Cu 2+
in vivo, when cultured in nutrient medium containing other heavy metal ions. Expression of the CUP1 promoter/ lacZ fusion gene was inhibited by all heavy metal ions tested, especially Cd 2+ and Mn 2+. By adding Cd 2+ and Mn 2+ at 10 M concentration, the -galactosidase activity decreased by about 80% and 50% of the maximum induction observed with 1 mM CuSO 4, respectively. Furthermore, cell growth was markedly inhibited by combinations of 1 mM-Cu 2+ and 1 M-Cd 2+. Therefore, the yeast S. cerevisiae could not rely on MT synthesis as one of the copper-resistance mechanisms, when grown in a Cd 2+ environment. In contrast, the presence of Mn 2+ in the nutrient medium showed alleviation rather than growth inhibition by high concentrations of Cu 2+. The recovery from growth inhibition by Mn 2+ was due to decreased Cu 2+ accumulation. Inhibitory concentrations of Co 2+, Ni 2+ and Zn 2+ on expression of the CUP1p/ lacZ fusion gene were at least one order of magnitude higher than that of Cd 2+ and Mn 2+. These results are discussed in relation to Cu 2+ transport and Cu-induced MT synthesis in the copper-resistance mechanism of the yeast S. cerevisiae. 相似文献
8.
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
9.
Complexes formed by reduced glutathione (GSH) with metal cations (Cr 2+, Mn 2+,Fe 2+,Co 2+,Ni 2+,Cu 2+,Zn 2+,Cd 2+,Hg 2+) were systematically investigated by the density functional theory (DFT). The results showed that the interactions of the metal cations with GSH resulted in nine different stable complexes and many factors had an effect on the binding energy. Generally, for the same period of metal ions, the binding energies ranked in the order of Cu 2+>Ni 2+>Co 2+>Fe 2+>Cr 2+>Zn 2+>Mn 2+; and for the same group of metal ions, the general trend of binding energies was Zn 2+>Hg 2+>Cd 2+. Moreover, the amounts of charge transferred from S or N to transition metal cations are greater than that of O atoms. For Fe 2+,Co 2+,Ni 2+,Cu 2+,Zn 2+,Cd 2+ and Hg 2+ complexes, the values of the Wiberg bond indices (WBIs) of M-S (M denotes metal cations) were larger than that of M-N and M-O; for Cr 2+ complexes, most of the WBIs of M-O in complexes were higher than that of M-S and M-N. Furthermore, the changes in the electron configuration of the metal cations before and after chelate reaction revealed that Cu 2+, Ni 2+,Co 2+ and Hg 2+ had obvious tendencies to be reduced to Cu +,Ni +,Co + and Hg + during the coordination process. 相似文献
10.
In this study, dried and humid fruiting bodies of Tremella fuciformis and Auricularia polytricha were examined as cost-effective biosorbents in treatment of heavy metals (Cd 2+, Cu 2+, Pb 2+, and Zn 2+) in aqueous solution. The humid T. fuciformis showed the highest capacity to adsorb the four metals in the multi-metal solutions. The Pb 2+ adsorption rates were 85.5%, 97.8%, 84.8%, and 91.0% by dried T. fuciformis, humid T. fuciformis, dried A. polytricha, and humid A. polytricha, respectively. The adsorption amount of Pb 2+ by dried and humid T. fuciformis in Cd 2+ + Pb 2+, Cu 2+ + Pb 2+, Pb 2+ + Zn 2+, Cd 2+ + Cu 2+ + Pb 2+, and Cd 2+ + Zn 2+ + Pb 2+ solutions were not lower than that in Pb 2+ solutions. The results suggested that in humid T. fuciformis, Cd 2+, Cu 2+, and Zn 2+ promoted the Pb 2+ adsorption by the biomass. In the multi-metal solutions of Cd 2+ + Cu 2+ + Pb 2+ + Zn 2+, the adsorption amount and rates of the metals by all the test biosorbents were in the order of Pb 2+ > Cu 2+ > Zn 2+ > Cd 2+. Compared with the pseudo first-order model, the pseudo second-order model described the adsorption kinetics much better,
indicating a two-step biosorption process. The present study confirmed that fruiting bodies of the jelly fungi should be useful
for the treatment of wastewater containing Cd 2+, Cu 2+, Pb 2+, and Zn 2+. 相似文献
11.
Two BODIPY derivative sensors for metal ion recognition containing 10-(4-hydroxyphenyl) ( L1) and 10-(3,4-dihydroxyphenyl) ( L2) were synthesized in a one-pot reaction of benzaldehyde derivative and 2,4-dimethylpyrrole in the presence of trifluoroacetic acid as catalyst. The binding abilities between these sensors and 50 equivalents of Na +, K +, Ag +, Ca 2+, Fe 2+, Co 2+, Ni 2+, Cu 2+, Zn 2+, Cd 2+, Pb 2+, Al 3+ and Cr 3+ ions were studied using UV–vis and fluorescent spectroscopic methods. Of all the metal ions tested, Al 3+ ion showed the greatest decrease in intensity in the spectra of the sensors, and therefore Al 3+ ion forms the strongest complex. The binding abilities of BODIPY receptors with Na +, Ag +, Ca 2+, Co 2+, Ni 2+, Cu 2+, Zn 2+ and Al 3+ ions were also investigated using density functional theory (DFT) calculations at B3LYP/LanL2DZ theoretical level. The calculated results point to the same conclusion. DFT calculations also provided the HOMO–LUMO energy levels, which can explain the spectrum change upon complexation. Figure Graphical structure, fluorescent spectra, frontier orbital energy diagrams and electron-transfer paths in sensor L1, and after attachment with Al 3+ ion. 相似文献
12.
The passive sorption of Pb +2, Cd +2, Zn +2, Co +2, Ni +2, and Mn +2 by isolated corn mitochondria was determined, and, except for Pb +2, the maximum sorption for each cation was about 58 nmol per milligram of protein. Sorption of Pb +2 was apparently ten times greater, but precipitation may have been the cause of this larger value. The effects of Pb +2, Cd +2, Zn +2, Co +2, and Ni +2 on acceptorless rates of electron transport for three substrates were determined. Greater than 50% inhibitions of oxidation were observed for succinate after additions of >0.1 m M Cd +2, Zn +2, or Pb +2: for NADH after additions of >0.5 m M Cd +2 or Zn +2; and for malate + pyruvate after additions of >0.1 m M Cd +2. Some inhibition of the rate of substrate oxidation was observed for most cations at higher concentrations. Coupling, as measured by ADP/O ratios, was inhibited at lowest concentrations by Cd +2 or Zn +2 and at higher concentrations by Co +2 or Ni +2. Substantial swelling of mitochondria oxidizing succinate was observed following additions of O.1 m M Cd +2 or Pb +2, Correlations are drawn between the effects of Pb +2, Cd +2, Zn +2, Co +2, and Ni +2 and their sorption to mitochondrial membranes. 相似文献
13.
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
14.
Rat liver and kidney tissue slices incubated with N-acetyl [ 3H]mannosamine incorporated radioactivity into free and bound N-acetylneuraminic acid and CMP- N-acetylneuraminic acid (CMP-NeuAc). Liver and kidney also incorporated radioactivity from intravenously injected [ 3H]ManNAc into N-acetylneuraminic acid and CMP-NeuAc. From the decrease in the specific radioactivity of CMP-NeuAc after a single injection of N-acetyl[ 3H]mannosamine the half-life of CMP-NeuAc was determined. From this half-life and the pool size of CMP-NeuAc a synthesis rate of CMP-NeuAc was calculated, being 1.2 nmol/min/g wet weight of kidney. In previous experiments a value of 1.0 nmol/min/g wet weight was determined for liver [Ferwerda et al. (1983) Biochem J 216: 87–92]. The synthesis rate of CMP-NeuAc in vivo was in the same range as the synthesis rate calculated from the turnover of bound N-acetylneuraminic acid, which was 2.7 and 0.4 nmol/min/g wet weight for liver and kidney respectively.The assay conditions for UDP- N-acetylglucosamine 2-epimerase and N-acetylmannosamine kinase were adapted to measure low activities in vitro. It appeared that the kinase activity detected in kidney can synthesize N-acetylmannosamine6-phosphate at a rate sufficient for the observed production of N-acetylneuraminic acid in vivo. Also a low, but measurable activity of UDP- N-acetylglucosamine 2-epimerase was detected in kidney in vitro, suggesting that the biosynthetic pathway of N-acetylneuraminic acid in kidney is the same as in liver. The synthesis rate of N-acetylneuraminic acid in liver determined in vivo is approximately 12 times slower than the maximal potential rate calculated from the activities of the N-acetylneuraminic acid (precursor-) forming enzymes as detected in vitro. This indicates that in liver in vivo the enzymes are working far below their maximal capacity. 相似文献
15.
A soluble fraction of rat liver converts glucosamine and N-acetylglucosamine in the presence of ATP and UTP to N-acetylneuraminic acid. This system, when supplemented with CTP, forms CMP- N-acetylneuraminic acid in high yield. Nicotinamide was found to enhance the synthesis of UDP- N-acetylglucosamine and N-acetylneuraminic acid. Kinetic analysis reveals N-acetylglucosamine 6-phosphate, UDP- N-acetylglucosamine, N-acetylmannosamine, N-acetylmannosamine 6-phosphate and N-acetylneuraminic acid 9-phosphate as intermediates. Under certain experimental conditions, however, an epimerisation of N-acetylglucosamine to N-acetylmannosamine was seen. 相似文献
16.
The effects of eight divalent metal ions on fully neutralized poly(S-carboxyethyl-l-cysteine) have been studied by means of circular dichroism. Four ionic species (Cd 2+, Cu 2+, Zn 2+ and Ni 2+) effectively induce the β-form, while the other four species (Co 2+, Ba 2+, Ca 2+ and Mg 2+) are not effective. Specifically, Mg(ClO 4) 2 is ineffective, even at 1.86 m. The effect of Cu 2+ ions on the polypeptide conformation is significant at pH values other than in the neural range. Comparison of the present results with previous ones from the lower side chain homologue, poly(S-carboxymethyl-l-cysteine), shows that Cd 2+ and Zn 2+ ions are more effetive but Co 2+ ions are much less effective in the polypeptide studied here. Random coils of poly(S-carboxyethyl-l-cysteine) are more soluble while the β-form is less soluble compared with the respective conformations of the lower side-chain homologue. 相似文献
17.
In was found that an intracellular ribonuclease was present as an inactive form in the fresh mycelium of Asp. oryzae. It was about 3 times activated either by 3 m urea or by the autolysis of mycelium at 30°C for 20 hr. The optimum pH of the ribonuclease activity was 8.3. It was heat sensitive (60°C, 10 min), and completely inhibited by 5 m m EDTA. It was activated by 1 m m Mg 2+ and inhibited by Zn 2+, Ca 2+, Cd 2+, Co 2+ and Cu 2+. 相似文献
18.
Toxicities of binary mixtures of Cu 2+, Cd 2+, benzo(a)pyrene [B(a)P] and N-ethylmaleimide (NEM) were screened using the in vitro neutral red (NR) assay to test the hypothesis that combined toxicity is more than or less than additive relative to the influence of each mixture constituent on toxicant uptake and brown cell lysosomal membrane stability. Significant cytotoxicity was observed at 25 mol/L Cu 2+, 500 mol/L Cd 2+ and 25 mol/L NEM. B(a)P at 12 mol/L exerted no toxicity under the conditions of the assay. Interactions between Cu 2+ and NEM, between Cd 2+ and NEM, and between Cd 2+ and B(a)P significantly influenced brown cell survival. Comparison of observed joint toxicity with estimates made using a model of independent joint action indicates that interactive effects are less than additive in character. The 3-way interaction involving Cu 2+, B(a)P, and NEM also affected brown cell survival to a statistically significant degree. However, the interactive cytotoxicity of this mixture is attributable mainly to the combined effect of Cu 2+ and NEM. Results also indicate that new. hypotheses and additional experimentation are needed to understand the interactive toxicity of mixture constituents.Abbreviations PAH
polyaromatic hydrocarbon
- NEM
N-ethylmaleimide
- NR
neutral red
- B(a)P
benzo(a)pyrene 相似文献
19.
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
20.
Acetone fractionation of Bacillus lentus culture filtrate yielded the highest -amylase activity and the 66.6% fraction reached 13-fold that of the crude enzyme preparation. Gel filtration and ion exchange chromatography afforded a pure -amylase (relative molecular mass, 42 000). The pure enzyme was highly active on starch and dextrin. It produced a mixture of oligosaccharides as major products of starch hydrolysis. Maximal activity was reached at 70° C and pH 6.1. Ca 2+, Na +, K + and Sr 2+ ions stabilized or slightly stimulated the enzyme whereas Ag +, Co 2+, Hg 2+, Zn 2+, Cd 2+ and Fe 3+ ions strongly inhibited the activity. The enzyme contained 16 amino acids, of which aspartic and glutamic acids were present in the highest proportions.
Correspondence to: S. H. Omar 相似文献
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