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1.
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
2.
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
3.
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
4.
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
5.
Titrations of the quenching of the tryptophan fluorescence of yeast hexokinase isozymes P-I and P-II by Mg 2+, Mn 2+, Ca 2+, Cd 2+, and Zn 2+ ions and by glucose in the presence of each of these ions (10mM) were performed at pH 5.5 and 6.5 at 20°C. At the higher pH there was a reversal of the type of glucose-binding cooperativity for P-II from negative to positive when either Mn 2+ or Ca 2+ was present in the buffered isozyme solution before the glucose titration, whereas Mg 2+ caused the glucose binding to become noncooperative. Zn 2+ and Cd 2+ decreased the glucose quenching of P-II fluorescence drastically at pH 5.5, from a value of 15% in buffer to only 4%. Thus, only these two ions, of the five studied, cause the conformation change that results in quenching of the glucose-quenchable cleft tryptophan of P-II. Glucose binding to the P-I isozyme exhibited positive cooperativity in the presence of either Ca 2+, Mg 2+, or Mn 2+, as well as in buffer alone, at both pH's. At the lower pH, Ca 2+ enhanced the efficiency of glucose quenching of P-I fluorescence several-fold, while Mn 2+ increased it only about 40% and Mg 2+ not at all. Further, Ca 2+ raised the degree of cooperativity (Hill coefficient) of glucose binding to P-I at this pH from the value of 1.42 in buffer and in the presence of Mg 2+ and Mn 2+ to 1.94, i.e., almost up to the highest possible value, 2, for dimeric hexokinase. However, at pH 6.5 the Ca 2+ effect on the cooperativity was negligible, while Mg 2+ and Mn 2+ decreased the coefficient from 1.6 in buffer to about 1.4. The biological implications of these diverse metal ion effects are discussed. 相似文献
6.
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
7.
1. Pyruvate kinase (ATP–pyruvate phosphotransferase, EC 2.7.1.40) from Ehrlich ascites-tumour cells was purified approximately fivefold by chromatography on DEAE-cellulose. The enzyme was shown to have an absolute requirement for one univalent and for one bivalent metal ion. 2. The univalent metal ion requirements were satisfied by K +, Rb + or NH 4+; Na + and Cs + were weak activators but Li + was inactive. 3. Ca 2+ exhibited `non-competitive' and `apparent competitive' effects in relation to the K + activation. 4. The bivalent metal ion requirements were satisfied by Mg 2+, Mn 2+ or Co 2+; Ba 2+, Sr 2+, Ca 2+, Ni 2+, Be 2+ and Cu 2+ were inactive. Mn 2+ and Co 2+ were better activators than Mg 2+. 5. The bivalent metal ion requirements of purified pyruvate kinase from rabbit muscle were satisfied by Mg 2+, Mn 2+, Co 2+ and to a smaller extent by Ni 2+. Mn 2+ and Co 2+ were better activators than Mg 2+. 6. Ca 2+ competitively inhibited the activation by Mg 2+, Mn 2+ and Co 2+ for both the tumour and rabbit enzymes. 7. It is concluded that there are no significant differences in metal ion specificity between the tumour and rabbit enzymes. 8. The possible role of metal ions in regulating enzymic and metabolic activities is considered further. 相似文献
8.
The involvement of Ca 2+ in the response to high Mn 2+, Co 2+, Ni 2+, Cu 2+, Zn 2+, Cd 2+, and Hg 2+ was investigated in Saccharomyces cerevisiae. The yeast cells responded through a sharp increase in cytosolic Ca 2+ when exposed to Cd 2+, and to a lesser extent to Cu 2+, but not to Mn 2+, Co 2+, Ni 2+, Zn 2+, or Hg 2+. The response to high Cd 2+ depended mainly on external Ca 2+ (transported through the Cch1p/Mid1p channel) but also on vacuolar Ca 2+ (released into the cytosol through the Yvc1p channel). The adaptation to high Cd 2+ was influenced by perturbations in Ca 2+ homeostasis. Thus, the tolerance to Cd 2+ often correlated with sharp Cd 2+-induced cytosolic Ca 2+ pulses, while the Cd 2+ sensitivity was accompanied by the incapacity to rapidly restore the low cytosolic Ca 2+. 相似文献
9.
The voltage-gated proton channel Hv1 functions as a dimer, in which the intracellular C-terminal domain of the protein is responsible for the dimeric architecture and regulates proton permeability. Although it is well known that divalent metal ions have effect on the proton channel activity, the interaction of divalent metal ions with the channel in detail is not well elucidated. Herein, we investigated the interaction of divalent metal ions with the C-terminal domain of human Hv1 by CD spectra and fluorescence spectroscopy. The divalent metal ions binding induced an obvious conformational change at pH 7 and a pH-sensitive reduction of thermostability in the C-terminal domain. The interactions were further estimated by fluorescence spectroscopy experiments. There are at least two binding sites for divalent metal ions binding to the C-terminal domain of Hv1, either of which is close to His 244 or His 266 residue. The binding of Zn 2+ to the two sites both enhanced the fluorescence of the protein at pH 7, whereas the binding of other divalent metal ions to the two sites all resulted fluorescence quenching. The orders of the strength of divalent metal ions binding to the two sites from strong to weak are both Co 2+, Ca 2+, Ni 2+, Mg 2+, and Mn 2+. The strength of Ca 2+, Co 2+, Mg 2+, Mn 2+ and Ni 2+ binding to the site close to His 244 is stronger than that of these divalent metal ions binding to the site close to His 266. 相似文献
10.
Polyesters obtained from 2,5-dihydroxyterephthalic acid and 1, n-alkanediols were used to complexate the metal ions Mg 2+, Ca 2+, Sn 2+, Pb 2+, Ga 3+, In 3+, Bi 3+, Si 4+, Ce 3+, UO 22+, Mn 2+, Mn 3+, Co 2+, Ni 2+, Cu 2+, Zn 2+ and Cd 2+. The metal ions are always six-coordinated with additional ligands (mostly H 2O) besides the four from the polyester system. The H 2O-ligands can be removed by heating in vacuum, as was proven for the complexes of Mn 2+, Co 2+, Ni 2+ and Cu 2+, and are added again in moist air. For the waterfree Ni 2+-complex a tetrahedral surrounding is suggested by magnetic measurements. Polymerization degrees of the polyesters were found to be 30–70 by the membrane osmometric method. Thermal stabilities of the metal complexes (200– 300 °C) are less than those of the polyesters themselves (300–350 °C). 相似文献
11.
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
12.
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
13.
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
14.
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
15.
The aim of this paper was to describe the effect of various metal ions on the activity of protocatechuate 3,4-dioxygenase from Stenotrophomonas maltophilia KB2. We also compared activity of different dioxygenases isolated from this strain, in the presence of metal ions, after induction by various aromatic compounds. S. maltophilia KB2 degraded 13 mM 3,4-dihydroxybenzoate, 10 mM benzoic acid and 12 mM phenol within 24 h of incubation. In the presence of dihydroxybenzoate and benzoate, the activity of protocatechuate 3,4-dioxygenase and catechol 1,2-dioxygenase was observed. Although Fe 3+, Cu 2+, Zn 2+, Co 2+, Al 3+, Cd 2+, Ni 2+ and Mn 2+ ions caused 20–80 % inhibition of protocatechuate 3,4-dioxygenase activity, the above-mentioned metal ions (with the exception of Ni 2+) inhibited catechol 1,2-dioxygenase to a lesser extent or even activate the enzyme. Retaining activity of at least one of three dioxygenases from strain KB2 in the presence of metal ions makes it an ideal bacterium for bioremediation of contaminated areas. 相似文献
16.
In inside-out red cell membrane vesicles ATP-dependent calcium transport is activated by the divalent metal ions Mg 2+, Mn 2+, Co 2+, Ni 2+ and Fe 2+. This activation is based on the formation of Me 2+-ATP complexes which can serve as energy-donor substrates for the calcium pump, and probably, satisfy the requirement for free Me 2+ in this transport process. Higher Me 2+ concentrations inhibit calcium transport with various efficiencies. Mn 2+ directly competes with Ca 2+ at the transport site, while other divalent metal ions investigated have no such effect. The formation of the hydroxylamine-sensitive phosphorylated intermediate (EP) of the red cell membrane calcium pump from [γ- 32P]ATP is induced by Ca 2+ while rapid dephosphorylation requires the presence of Mg 2+. At higher concentrations Mn 2+ and Ni 2+ inhibit predominantly the formation of EP, while Co 2+ and Fe 2+ block dephosphorylation. The possible sites and nature of the divalent metal interactions with the red cell calcium pump are discussed. Hydroxylamine-insensitive membrane phosphorylation in inside-out vesicles from [γ- 32P]ATP is significantly stimulated by Mn 2+ and Co 2+, as compared to that produced by Mg 2+, Fe 2+ and Ni 2+. Part of this labelling is found in phospholipids, especially in phosphatidylinositol. The results presented for the metal dependency of protein and lipid phosphorylation in red cell membranes may help in the characterization of ATP consumptions directly related to the calcium pump and those involved in various regulatory processes. 相似文献
18.
This paper reports the synthesis of azomethine-modified gold nanoparticles with azomethine (azomethine-AuNPs) in aqueous media, which were characterized by FT-IR spectroscopy, ultraviolet–visible spectroscopy (UV-Vis), dynamic light scattering (DLS), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). The azomethine-AuNPs were employed as colorimetric for Cr3+ and Co2+ ions at pH 6.2–7.5 and 8.1–9.1, at room temperature in aqueous solution. In the presence of Cr3+ and Co2+, the azomethine-AuNPs induce aggregation of the nanoparticles. Upon aggregation, the surface plasmon absorption band red-shifts so that the nanoparticle solution appears a blue color. The sensitivity of azomethine-AuNPs towards other metal ions, Mg2+, Mn2+, Cr6+, Na+, Ni2+, Ag+, Al3+, Ca2+, Cd2+, Cu2+, Fe2+, Fe3+, Hg2+, Cd2+, K+, Co3+, Ni2+, Pb2+, and Zn2+ are negligible. This highly selective sensor allows a direct quantitative assay of Co2+ and Cr3+ with colorimetric detection limits of 83.22 and 108 nM, respectively. 相似文献
19.
Summary The toxicity of chromium and tin on growth, photosynthetic carbon-fixation, oxygen evolution, heterocyst differentiation and nitrogenase activity of Anabaena doliolum and its interaction with bivalent cations has been studied. Some interacting cations, viz. Ca 2+, Mg 2+ and Mn 2+, substantially antagonised the toxic effects of chromium and tin with reference to growth, heterocyst differentiation and nitrogenase activity in the following hierarchal sequence: Ca 2+ > Mg 2+ > Mn 2+. However, the sequence of hierarchy was Mg 2+ > Ca 2+ > Mn 2+ for carbon fixation and Mn 2+ > Mg 2+ > Ca 2+ for photosynthetic oxygen evolution. Synergistically inhibitory patterns were noticed for all the parameters, viz. growth, 14CO 2 uptake, oxygen evolution, heterocyst differentiation and nitrogenase activity of A. doliolum when Ni 2+, Co 2+ and Zn 2+ were combined with the test metals in the growth medium. These cations followed the following sequence of synergistic inhibition: Ni 2+ > Co 2+ > Zn 2+. Among all the interacting cations, Ca 2+, Mg 2+ and Mn 2+ exhibited antagonistic effects which relieved the test cyanobacterium from metal toxicity. In contrast to this, Ni 2+, CO 2+ and Zn 2+ showed synergistic inhibition which potentiating the toxicity of test metals in the N 2-fixing cyanobacterium A. doliolum. It is evident from the present study that bivalent cations, viz. Ca 2+, Mg 2+, Mn 2+, Ni 2+, Co 2+ and Zn 2+, may appreciably regulate the toxicity of heavy metals in N 2-fixing cyanobacteria if present in aquatic media. 相似文献
20.
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
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