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1.
Bacterial plasmids encode resistance systems for toxic metal ions, including Ag +, AsO 2-, AsO 43-, Cd 2+, Co 2+, CrO 42-, Cu 2+ Hg 2+, Ni 2+, Pb 2+, Sb 3+, TeO 32-, Tl + and Zn 2+. The function of most resistance systems is based on the energy-dependent efflux of toxic ions. Some of the efflux systems are ATPases and others are chemiosmotic cation/proton antiporters. The Cd 2+-resistance ATPase of Gram-positive bacteria (CadA) is membrane cation pump homologous with other bacterial, animal and plant P-type ATPases. CadA has been labeled with 32P from [ α- 32p]ATP and drives ATP-dependent Cd 2+ (and Zn 2+) uptake by inside-out membrane vesicles (equivalent to efflux from whole cells). Recently, isolated genes defective in the human hereditary diseases of copper metabolism, namely Menkes syndrome and Wilson's disease, encode P-type ATPases that are more similar to bacterial CadA than to other ATPases from eukaryotes. The arsenic resistance efflux system transports arsenite [As(III)], alternatively using either a double-polypeptide (ArsA and ArsB) ATPase or a single-polypeptide (ArsB) functioning as a chemiosmotic transporter. The third gene in the arsenic resistance system, arsC, encodes an enzyme that converts intracellular arsenate [As(V)] to arsenite [As(III)], the substrate of the efflux system. The triple-polypeptide Czc (Cd 2+, Zn 2+ and Co 2+) chemiosmotic efflux pump consists of inner membrane (CzcA), outer membrane (CzcC) and membrane-spanning (CzcB) proteins that together transport cations from the cytoplasm across the periplasmic space to the outside of the cell. 相似文献
2.
Glutathione S-transferases (GSTs) are an important enzyme family which play a critical role in detoxification system. In our study, GST was purified from muscle tissue of Chalcalburnus tarichii Pallas with 301.5-fold purification and 19.07% recovery by glutathione agarose affinity chromatography. The purity of enzyme was checked by sodium dodecyl sulfate–polyacrylamide gel electrophoresis, showing a two band, because of having heterodimer structure. KM values were 1.59 and 0.53?mM for 1-chloro-2,4-dinitrobenzene (CDNB) and glutathione (GSH), respectively. Vmax values for CDNB and GSH were also determined as 5.58 and 1.88?EU/mL, respectively. In addition, inhibition effects of Ag +, Cu 2+, Cd 2+, Fe 3+, Pb 2+, Cr 2+, Co 2+ and Zn 2+ metal ions were investigated on the enzyme activity and IC 50, K i values were calculated for these metal ions. 相似文献
3.
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
4.
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
5.
Triethyl thiophosphate (tetp) invariably forms adducts with various metal perchlorates (M=Mg 2+, Al 3+, Cr 3+, Mn 2+, Fe 2+, Fe 3+, Co 2+, Ni 2+, Cu 2+, Zn 2+, Cd 2+) at 35–40°C in ethanol-triethyl orthoformate (teof). Only certain of these adducts, which involve S-bonded tetp in the thione form for soft or borderline metal ions and O-bonded tetp in the thiol tautomeric form for hard metal ions, could be isolated in solid form, owing to their tendency to decompose yielding diethylthiophosphato (detp) metal complexes and ethyl perchlorate, at temperatures ranging between ambient and 80–90°C, depending on the metal ion. Several well-defined detp and detpperchlorato metal complexes were obtained by heating solutions of mixtures of tetp and metal perchlorates in ethanol-teof at 80–90°C, and characterized. In most cases, linear polymeric or dimeric complexes involving double or triple bridges of O,S-bonded bidentate detp between adjacent metal ions were isolated. However, in a number of occasions, heavily hydrated monomeric species, containing terminal S-bonded detp were obtained. 相似文献
6.
Bacterial chromosomes have genes for transport proteins for inorganic nutrient cations and oxyanions, such as NH 4
+, K +, Mg 2+, Co 2+, Fe 3+, Mn 2+, Zn 2+ and other trace cations, PO 4
3-, SO 4
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 + AsO 2
-, AsO 4
3-, Cd 2+, Co 2+, CrO 4
2−, Cu 2+, Hg 2+, Ni 2+, Pb 2+, TeO 3
2−, TI + and Zn 2+. 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 Cd 2+-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 Cd 2+ (and Zn 2+) 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 Cd 2+, Zn 2+ and Co 2+. 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
7.
A new rhodamine–ethylenediamine–nitrothiourea conjugate (RT) was synthesized and its sensing property as a fluorescent chemodosimeter toward metal ions was explored in water media. Analytical results from absorption and fluorescence spectra revealed that the addition of Hg 2+ ions to the aqueous solution of the chemodosimeter RT caused a distinct fluorescence OFF–ON response with a remarkable visual color change from colorless to pink; however, no clear spectral and color changes were observed from other metal ions including: Zn 2+, Cu 2+, Cd 2+, Pb 2+, Ag +, Fe 2+, Cr 3+, Co 3+, Ni 2+, Ca 2+, Mg 2+, K + and Na +. The sensing results and the molecular structure suggested that a Hg 2+‐induced a desulfurization reaction and cyclic guanylation of the thiourea moiety followed by ring‐opening of the rhodamine spirolactam in RT are responsible for a distinct fluorescence turn‐on signal, indicating that RT is a remarkably sensitive and selective chemodosimeter for Hg 2+ ions in aqueous solution. Hg 2+ within a concentration range from 0.1 to 25 μM can be determined using RT as a chemodosimeter and a detection limit of 0.04 μM is achieved. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
8.
In this study, d ‐penicillamine‐functionalized graphene quantum dots (DPA‐GQD) has been synthesized, which significantly increases the fluorescence intensity of GQD. We used this simple fluorescent probe for metal ions detection in human plasma samples. Designed DPA‐GQD respond to Hg 2+, Cu 2+, Au 2+, Ag +, Co 2+, Zn 2+, and Pb 2+ with high sensitivity. The fluorescence intensity of this probe decreased significantly in the presence of metal ions such as, Hg 2+, Cu 2+, Au 2+, Ag +, Co 2+, Zn 2+, and Pb 2+. In this work, a promising probe for ions monitoring was introduced. Moreover, DPA‐GQD probe has been tested in plasma samples. The functionalized DPA‐GQDs exhibits great promise as an alternative to previous fluorescent probes for bio‐labeling, sensing, and other biomedical applications in aqueous solution. 相似文献
9.
The capabilities of a new class of immobilized ( im) metal ion chelate complexes (IMCCs), derived from 1,4,7‐triazacyclononane (tacn), bis(1,4,7‐triazacyclononyl) ethane (dtne) and bis(1,4,7‐triazacyclononyl)propane (dtnp) complexed with the borderline metal ions Cu 2+, Ni 2+, Zn 2+, Mn 2+, Co 2+, and Cr 3+, for the purification of proteins have been investigated. In particular, the binding behavior of a model protein, the C‐terminal hexahistidine tagged recombinant fusion protein Schistosoma japonicum glutathione S‐transferase‐ Saccharomyces cerevisiae mitochondrial ATP synthase δ‐subunit (GST‐δATPase‐His 6), with these new immobilized metal ion affinity chromatographic (IMAC) sorbents was compared to the properties of a conventional sorbent, derived from immobilized Ni(II)‐nitrilotriacetic acid ( im‐Ni 2+‐NTA). Investigations using the recombinant GST‐δATPase‐His 6 and recombinant S. japonicum glutathione S‐transferase (GST) lacking a hexahistidine tag have confirmed that the C‐terminal tag hexahistidine residues were required for the binding process to occur with these IMAC systems. The results also confirm that recombinant fusion proteins such as GST‐δATPase‐His 6 can be isolated in high purity with these IMAC systems. Moreover, these new macrocyclic systems manifest different selectivity features as a function of pH or ionic strength when compared to the conventional, unconstrained iminodiacetic acid (IDA) or NTA chelating ligands, complexed with borderline metal ions such as Cu 2+ or Ni 2+, as IMAC systems. Biotechnol. Bioeng. 2009;103: 747–756. © 2009 Wiley Periodicals, Inc. 相似文献
10.
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
11.
Glucose‐6‐phosphate dehydrogenase (G6PD) is the first enzyme on which the pentose phosphate pathway was checked. In this study, purification of a G6PD enzyme was carried out by using rat erythrocytes with a specific activity of 13.7 EU/mg and a yield of 67.7 and 155.6‐fold by using 2′,5′‐ADP Sepharose‐4B affinity column chromatography. For the purpose of identifying the purity of enzyme and molecular mass of the subunit, a sodium dodecyl sulfate‐polyacrylamide gel electrophoresis was carried out. The molecular mass of subunit was calculated 56.5 kDa approximately. Then, an investigation was carried out regarding the inhibitory effects caused by various metal ions (Fe 2+, Pb 2+, Cd 2+, Ag +, and Zn 2+) on G6PD enzyme activities, as per Beutler method at 340 nm under in vitro conditions. Lineweaver–Burk diagrams were used for estimation of the IC 50 and Ki values for the metals. Ki values for Pb +2, Cd +2, Ag +, and Zn +2 were 113.3, 215.2, 19.4, and 474.7 μM, respectively. 相似文献
12.
A water‐soluble, high‐output fluorescent sensor, based on a lumazine ligand with a thiophene substituent for Cd 2+, Hg 2+ and Ag + metal ions, is reported. The sensor displays fluorescence enhancement upon Cd 2+ binding (log β = 2.79 ± 0.08) and fluorescence quenching by chelating with Ag + and Hg 2+ (log β = 4.31 ± 0.15 and 5.42 ± 0.1, respectively). The mechanism of quenching is static and occurs by formation of a ground‐state non‐fluorescent complex followed by rapid intersystem crossing. The value of the Stern–Volmer quenching rate constant ( kq) by Ag + ions is close to 6.71 × 10 12 mol/L/s at 298 K. The thermodynamic parameters ( ΔG, ΔH and ΔS) were also evaluated and indicated that the complexation process is spontaneous, exothermic and entropically favourable. The quantitative linear relationship between the softness values of Klopman ( σK) or Ahrland ( σA) and the experimental binding constants ( β) being in the order of Hg 2+ > Ag + > Cd 2+ suggests that soft–soft interactions are the key for the observed sensitivity and selectivity in the presence of other metal ions, such as: Pb 2+, Ni 2+, Mn 2+, Cu 2+, Co 2+, Zn 2+ and Mg 2+ ions. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
13.
Yersiniabactin (Ybt) is a metal‐binding natural product that has been re‐purposed for water treatment. The early focus of this study was the characterization of metal binding breadth attributed to Ybt. Using LC‐MS analysis of water samples exposed to aqueous and surface‐localized Ybt, quantitative assessment of binding was completed with metals that included Pd 2+, Mg 2+, and Zn 2+. In total, Ybt showed affinity for 10 metals. Next, Ybt‐modified XAD‐16N resin (Ybt‐XAD) was utilized to quantify the affinity for metal removal, showing a rank order of Fe 3+ > Ga 3+ > Ni 2+ > Cu 2+ > Cr 2+≈Zn 2+ > Co 2+ > Pd 2+ > Mg 2+ > Al 3+, and in the applied treatment of wastewater from a local precious metal plating company, showing selective removal of nickel from the aqueous effluent. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:1548–1554, 2017 相似文献
14.
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
15.
In liver homogenate the biosynthesis of N-acetylneuraminic acid using N-acetylglucosamine as precursor can be followed stepwise by applying different chromatographic procedures. In this cell-free system 16 metal ions (Zn 2+, Mn 2+, La 3+, Co 2+, Cu 2+, Hg 2+, VO
3
–
, Pb 2+, Ce 3+, Cd 2+, Fe 2+, Fe 3+, Al 3+, Sn 2+, Cs + and Li +) and the selenium compounds, selenium(IV) oxide and sodium selenite, have been checked with respect to their ability to influence a single or possible several steps of the biosynthesis of N-acetylneuraminic acid. It could be shown that the following enzymes are sensitive to these metal ions (usually applied at a concentration of 1 mmoll –1): N-acetylglucosamine kinase (inhibited by Zn 2+ and vandate), UDP- N-acetylglucosamine-2-epimerase (inhibited by zn 2+, Co 2+, Cu 2+, Hg 2+, VO
3
–
, Pb 2+, Cd 2+, Fe 3+, Cs +, Li +, selenium(IV) oxide and selenite), and N-acetylmannosamine kinase (inhibited by Zn 2+, Cu 2+, Cd 2+, and Co 2+). Dose dependent measurements have shown that Zn 2+, Cu 2+ and selenite are more efficient inhibitors of UDP- N-acetylglucosamine-2-epimerase than vanadate. As for the N-acetylmannosamine kinase inhibition, a decreasing inhibitory effect exists in the following order Zn 2+, Cd 2+, Co 2+ and Cu 2+. In contrast, La 3+, Al 3+ and Mn 2+ (1 mmoll –1) did not interfere with the biosynthesis of N-acetylneuraminic acid. Thus, the conclusion that the inhibitory effect of the metal ions investigated cannot be regarded as simply unspecific is justified.Dedicated to Professor Theodor Günther on the occasion of his 60th birthday 相似文献
16.
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
17.
In this work, the carbonic anhydrase (CA) enzyme was purified from Kangal Akkaraman sheep in Sivas, Turkey with specific activity value of 6681.57 EU/mg and yield of 14.90% with using affinity column chromatography. For designating the subunit molecular mass and enzyme purity, sodium dodecyl sulfate polyacrylamide gel electrophoresis method was used and single band for this procedure was obtained. The molecular mass of CA enzyme was found as 28.89 kDa. In this study, the optimum temperature and optimum pH were obtained from 30 and 7.5. Vmax and Km values for p‐nitrophenylacetate substrate of the CA were determined from Lineweaver–Burk graphs. Additionally, the inhibitory results of diverse heavy metal ions (Hg +, Fe 2+, Pb 2+, Co 2+, Ag +, and Cu 2+) on sheep were studied. Indeed, CA enzyme activities of Kangal sheep were investigated with using esterase procedure under in vitro conditions. The heavy metal concentrations inhibiting 50% of enzyme activity (IC 50) and Ki values were obtained. 相似文献
18.
The ability of metal ions to cause physical aggregation of neutral solutions of bovine fibrinogen has been studied. Three categories were found: (a) ions (such as Ca 2+, Mg 2+ and Mn 2+) which did not cause aggregation even when present in 1–100 mm concentrations: (b) ions (such as Fe 2+, Cu 2+ and Ni 2+) which caused aggregation in the 0–10 mm concentration range, (c) ions (such as Hg 2+, Zn 2+, Cr 3+, La 3+) which caused aggregation in the 0–1000 μm concentration range. Aggregation occurs immediately the metal ion is brought into contact with the fibrinogen, and product formation reaches a steady state within 5 min. With the exception of Zn 2+, all the ions that caused aggregation exhibited a threshold concentration below which no observable aggregation took place. The threshold concentration for Hg 2+, the most effective ion studied, was 6 μm. Addition of excess EDTA caused resolubilization of the aggregated fibrinogen due to removal of the metal ions. Aggregation is thus thought to be a physical process initiated by binding of metal ions to those carboxyl groups in fibrinogen responsible for keeping the monomers apart in solution. The aggregation does not involve prior proteolytic degradation of the fibrinogen. 相似文献
19.
The effects of metal ions of the first-row transition and of alkaline earth metals on the DNA helix conformation have been studied by uv difference spectra, circular dichroism, and sedimentation measurements. At low ionic strength (10 ?3 M NaClO 4) DNA shows a maximum in the difference absorption spectra in the presence of Zn 2+, Mn 2+, Co 2+, Cd 2+, and Ni 2+ but not with Mg 2+ or Ca 2+. The amplitude of this maximum is dependent on GC content as revealed by detailed studies of the DNA-Zn 2+ complex of eight different DNA's. Pronounced changes also occur in the CD spectra of DNA transition metal complexes. A transition appears up to a total ratio of approximately 1 Zn 2+ per DNA phosphate at 10 ?3 M NaClO 4; then no further change was observed up to high concentrations. The characteristic CD changes are strongly dependent on the double-helical structure of DNA and on the GC content of DNA. Differences were also observed in hydrodynamic properties of DNA metal complexes as revealed by the greater increase of the sedimentation coefficient of native DNA in the presence of transition metal ions. Spectrophotometric acid titration experiments and CD measurements at acidic pH clearly indicate the suppression of protonation of GC base-pair regions on the addition of transition metal ions to DNA. Similar effects were not observed with DNA complexes with alkaline earth metal ions such as Mg 2+ or Ca 2+. The data are interpreted in terms of a preferential interaction of Zn 2+ and of other transition metal ions with GC sites by chelation to the N-7 of guanine and to the phosphate residue. The binding of Zn 2+ to DNA disappears between 0.5 M and 1 M NaClO 4, but complex formation with DNA is observable again in the presence of highly concentrated solutions of NaClO 4 (3?7.2 M NaClO 4) or at 0.5 to 2 M Mn 2+. At relatively high cation concentration Mg 2+ is also effective in changing the DNA comformation. These structural alterations probably result from both the shielding of negatively charged phosphate groups and the breakdown of the water structure along the DNA helix. Differential effects in CD are also observed between Mn 2+, Zn 2+ on one hand and Mg 2+ on the other hand under these conditions. The greater sensitivity of the double-helical conformation of DNA to the action of transition metal ions is due to the affinity of the latter to electron donating sites of the bases resulting from the d electronic configuration of the metal ions. An order of the relative phosphate binding ability to base-site binding ability in native DNA is obtained as follows: Mg 2+, Ba 2+, < Ca 2+ < Fe 2+, Ni 2+, Co 2+ < Mn 2+, Zn 2+ < Cd 2+ < Cu 2+. The metal-ion induced conformational changes of the DNA are explained by alternation of the winding angle between base pairs as occurs in the transition from B to C conformation. These findings are used for a tentative molecular interpretation of some effects of Zn 2+ and Mn 2+ in DNA synthesis reported in the literature. 相似文献
20.
Summary Rape, cucumber, wheat, oats and tomato were grown for one to two weeks in nutrient solutions with heavy metals added. Of the metal ions tested (Cr 3+, Cu 2+, Co 2+, CrO 4
2-, Ni 2+, Cd 2+, Pb 2+, Mn 2+, Zn 2+ and Ag +), manganese, nickel and lead exhibited the greatest mobility in cucumber plants, which resulted in the highest shoot/root concentration ratio. Silver was not translocated to the shoots of cucumber plants in measurable amounts.When the plants were grown with 1.0, 10 and 100 M cadmium or nickel in the solution, the shoot and root concentration increased 5–10 times if the metal ion concentration of the solution was increased 10 times.The plants showed great differences in cadmium and nickel uptake. In the shoot, the cadmium concentration increased in the order: oats = wheat < cucumber = rape < tomato, and in the root in the order: oats = wheat < cucumber = rape < tomato. The great uptake of cadmium and nickel by tomato is notable and agrees with other reports.The nickel, and especially the cadmium, concentration in roots and shoots increases with the age of the plant.The results are discussed and related to other investigations. The need for research on the uptake mechanisms of non-essential heavy metals is emphasized. re]19750415 相似文献
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