Computer simulation of Zn(II) speciation and effect of Gd(III) on Zn(II) speciation in human blood plasma

The speciation and distribution of Zn(II) and the effect of Gd(III) on Zn(II) speciation in human blood plasma were studied by computer simulation. The results show that, in normal blood plasma, the most predominant species of Zn(II) are [Zn(HSA)] (58.2%), [Zn(IgG)](20.1%), [Zn(Tf)] (10.4%), ternary complexes of [Zn(Cit)(Cys)] (6.6%) and of [Zn(Cys)(His)H] (1.6%), and the binary complex of [Zn(Cys)₂H] (1.2%). When zinc is deficient, the distribution of Zn(II) species is similar to that in normal blood plasma. Then, the distribution changes with increasing zinc(II) total concentration. Overloading Zn(II) is initially mainly bound to human serum albumin (HSA). As the available amount of HSA is exceeded, phosphate metal and carbonate metal species are established. Gd(III) entering human blood plasma predominantly competes for phosphate and carbonate to form precipitate species. However, Zn(II) complexes with phosphate and carbonate are negligible in normal blood plasma, so Gd(III) only have a little effect on zinc(II) species in human blood plasma at a concentration above 1.0×10⁻⁴ M.     

Structural and functional characterization of the Zn(II) site in dimethylargininase-1 (DDAH-1) from bovine brain. Zn(II) release activates DDAH-1

L-N(omega),N(omega)-dimethylarginine dimethylaminohydrolase-1 (DDAH-1) is a Zn(II)-containing enzyme that, through hydrolysis of side-chain methylated l-arginines, regulates the activity of nitric-oxide synthase. Herein we report the structural and functional properties of the Zn(II)-binding site in DDAH-1 from bovine brain. Activity measurements of the native and metal-free enzyme have revealed that the endogenously bound Zn(II) inhibits the enzyme. Native DDAH-1 could be fully or partially activated using various concentrations of phosphate, imidazole, histidine, and histamine, a process that is paralleled by the release of Zn(II). The slow activation of the enzyme by the bulky complexing agents EDTA and 1,10-phenantroline suggests that the Zn(II)-binding site is partially buried in the protein structure. The apparent Zn(II)-dissociation constant of 4.2 nm, determined by 19F NMR using the chelator 5F-BAPTA (1,2-bis(2-amino-5-fluorophenoxy)ethane-N,N,N',N'-tetraacetic acid), lies in the range of intracellular free Zn(II) concentrations. These results suggest a regulatory role for the Zn(II)-binding site. The coordination environment of the Zn(II) in DDAH-1 has been examined by Zn K-edge x-ray absorption spectroscopy. The extended x-ray absorption fine structure observed is consistent with Zn(II) being coordinated by 2 S and 2 N (or O) atoms. The biological implications of these findings are discussed.     

Comparative insight into the Zn(II)-, Cd(II)- and Cu(I)-binding features of the protozoan Tetrahymena pyriformis MT1 metallothionein

Tetrahymena pyriformis MT1 (TpyMT1) is a model among ciliate metallothioneins (MTs). Here, we report on the analytic (ICP-AES, GC-FPD), spectroscopic (CD, UV-Vis, Raman) and spectrometric (ESI-MS) characterization of its recombinant Cd(II)-, Zn(II)- and Cu(I)-complexes, and of those formed during in vitro Zn/Cd and Zn/Cu replacement. In the presence of Cd(II), TpyMT1 renders a major Cd 11-TpyMT1 species, which is also the final step reached in the in vitro Zn/Cd exchange process in Zn 11-TpyMT1. Spectroscopic data supports a different folding of the isostoichiometric Cd 11- and Zn 11-TpyMT1 complexes. Unexpectedly, TpyMT1 biosynthesis in Zn(II)-rich cultures was sensitive to the aeration degree, so that high oxygenation rendered undermetalated, partially-oxidized, complexes (Zn9-TpyMT1). Biosynthesis in Cu(I)-rich media rendered extremely heterogeneous mixtures of CuxZny-species (x+y=8-20), where the higher the aeration, the higher the Zn(II) content. The complexity of these samples was reproduced during the Zn/Cu replacement, as the number of generated species increased gradually with the addition of copper to Zn(11)-TpyMT1. According to our results, a clear preference of TpyMT1 for Cd(II) binding, rather than for Zn(II), and especially Cu(I) can be postulated. This character is totally consistent with the induction pattern of the TpyMT1 gene and the postulated role of TpyMT1 in Cd-detoxification.     

Zinc (Zn)-phosphorus (P) Interactions in Two Cultivars of Spring Wheat (Triticum aestivum L.) Differing in P Uptake Efficiency

Zinc-phosphorus (Zn-P) interactions were investigated in twowheat cultivars (Brookton and Krichauff) differing in P uptakeefficiency. The experiment was carried out in a growth chamber.Rock phosphate or CaHPO₄were used as P sources, and ammoniumnitrate or nitrate only as nitrogen sources. Two Zn levels wereused: 0.22 and 2.2 mg ZnSO₄.5H₂O kg^-1. The results confirmedthat Brookton had a higher P uptake efficiency than Krichauffunder low P conditions, irrespective of nitrogen and Zn supply.Zn supply had little effect on tissue P concentration and Puptake per unit of root weight in either cultivar, irrespectiveof nitrogen supply. An increase in P availability caused a significantreduction in Zn uptake per unit of root weight, and tissue concentrationof Zn in both cultivars. The reduction in tissue Zn concentrationcannot be explained entirely by a dilution effect. Zn uptakeby, and Zn concentrations in, Brookton (with high P uptake efficiency)were significantly lower than those of Krichauff. Zn concentrationsin Brookton were more sensitive to P uptake than those in Krichauff.It is suggested that high P uptake efficiency may depress plantuptake of Zn, and therefore cause a reduction in the concentration(density) of Zn in grains of wheats grown in low P (and possiblylow Zn) soils. Copyright 2001 Annals of Botany Company Phosphorus efficiency, translocation, uptake, zinc-phosphorus interaction, wheat     

Zn(II) metabolism in prokaryotes

It is difficult to over-state the importance of Zn(II) in biology. It is a ubiquitous essential metal ion and plays a role in catalysis, protein structure and perhaps as a signal molecule, in organisms from all three kingdoms. Of necessity, organisms have evolved to optimise the intracellular availability of Zn(II) despite the extracellular milieu. To this end, prokaryotes contain a range of Zn(II) import, Zn(II) export and/or binding proteins, some of which utilise either ATP or the chemiosmotic potential to drive the movement of Zn(II) across the cytosolic membrane, together with proteins that facilitate the diffusion of this ion across either the outer or inner membranes of prokaryotes. This review seeks to give an overview of the systems currently classified as altering Zn(II) availability in prokaryotes.     

Thionein/metallothionein control Zn(II) availability and the activity of enzymes

Fundamental issues in zinc biology are how proteins control the concentrations of free Zn(II) ions and how tightly they interact with them. Since, basically, the Zn(II) stability constants of only two cytosolic zinc enzymes, carbonic anhydrase and superoxide dismutase, have been reported, the affinity for Zn(II) of another zinc enzyme, sorbitol dehydrogenase (SDH), was determined. Its log K is 11.2 +/- 0.1, which is similar to the log K values of carbonic anhydrase and superoxide dismutase despite considerable differences in the coordination environments of Zn(II) in these enzymes. Protein tyrosine phosphatase 1B (PTP 1B), on the other hand, is not classified as a zinc enzyme but is strongly inhibited by Zn(II), with log K = 7.8 +/- 0.1. In order to test whether or not metallothionein (MT) can serve as a source for Zn(II) ions, it was used to control free Zn(II) ion concentrations. MT makes Zn(II) available for both PTP 1B and the apoform of SDH. However, whether or not Zn(II) ions are indeed available for interaction with these enzymes depends on the thionein (T) to MT ratio and the redox poise. At ratios [T/(MT + T) = 0.08-0.31] prevailing in tissues and cells, picomolar concentrations of free Zn(II) are available from MT for reconstituting apoenzymes with Zn(II). Under conditions of decreased ratios, nanomolar concentrations of free Zn(II) become available and affect enzymes that are not zinc metalloenzymes. The match between the Zn(II) buffering capacity of MT and the Zn(II) affinity of proteins suggests a function of MT in controlling cellular Zn(II) availability.     

Effect of praseodymium(III) on zinc(II) species in human interstitial fluid

A multiphase model of metal ion species in human interstitial fluid was constructed under physiological conditions. The effect of Pr(III) on Zn(II) species was studied. At the normal conditions, Zn(II) species mainly distribute in [Zn(HSA)], [Zn(IgG)], and [Zn(Cys)₂H]⁺. With the Pr(III) level increased, the apparent competition of Pr(III) for ligands lead to the redistribution of Zn(II) species.     

Insulinomimetic Zn complex (Zn(opt)2) enhances insulin signaling pathway in 3T3-L1 adipocytes

Zinc (Zn) is an essential trace element with multiple regulatory functions, involving insulin synthesis, secretion, signaling and glucose transport. Since 2000, we have proposed that Zn complexes with different coordination environments exhibit high insulinomimetic and antidiabetic activities in type 2 diabetic animals. However, the molecular mechanism for the activities is still unsolved. The purpose of this study was to reveal the molecular mechanism of several types of Zn complexes in 3T3-L1 adipocytes, with respect to insulin signaling pathway. Obtained results shows that bis(1-oxy-2-pyridine-thiolato)Zn(II), Zn(opt)2, with S(2)O(2) coordination environment induced most strongly Akt/protein kinase B (Akt/PKB) phosphorylation, in which the optimal phosphorylation was achieved at a concentration of 25 microM, and this Zn(opt)2-induced Akt/PKB phosphorylation was inhibited by wortmannin at 100 nM. Further, the phosphorylation was maximal at 5-10 min stimulation, in agreement with the Zn uptake which was also maximal at 5-10 min stimulation. The Akt/PKB phosphorylation was in concentration- and time-dependent manners. Zn(opt)2 was also capable to translocate GLUT4 protein to the plasma membrane. We conclude that Zn(opt)2 was revealed to exhibit both insulinomimetic and antidiabetic activities by activating insulin signaling cascade through Akt/PKB phosphorylation, which in turn caused the GLUT4 translocation from the cytosol to the plasma membrane.     

Nicotianamine forms complexes with Zn(II) in vivo

The non-proteinogenic amino acid nicotianamine (NA) is a major player in plant metal homeostasis. It is known to form complexes with different transition metals in vitro. Available evidence associates NA with translocation of Fe, and possibly other micronutrients, to and between different plant cells and tissues. To date, however, it is still extremely challenging to detect metal-ligand complexes in vivo because tissue disruption immediately changes the chemical environment and thereby the availability of binding partners. In order to overcome this limitation we used various Schizosaccharomyces pombe strains expressing a plant NAS gene to study formation of metal-NA complexes in vivo. Tolerance, accumulation and competition data clearly indicated formation of Zn(ii)-NA but not of Cu(ii)-NA complexes. Zn(ii)-NA was then identified by X-ray absorption spectroscopy (XAS). About half of the cellular Zn was found to be bound by NA in NAS-expressing cells while no NA-like ligands were detected by XAS in control cells not expressing NAS. Given the high conservation of eukaryotic metal homeostasis components, these results strongly suggest the possible existence of Zn(ii)-NA complexes also in planta. Reported observations implicating NA in plant Zn homeostasis would then indeed be attributable to direct interaction of Zn(ii) with NA rather than only indirectly to perturbations in Fe metabolism. Re-evaluation of extended X-ray absorption fine structure (EXAFS) spectra for the Zn hyperaccumulator Thlaspi caerulescens showed that NA is as expected not a major storage ligand for Zn. Instead it is hypothesized to be involved in efficient translocation of Zn to above-ground tissues in hyperaccumulators.     

Growth and Nutrient Uptake by Barley (Hordeum vulgare L. cv Herta): Studies Using an N-(2-Hydroxyethyl)ethylenedinitrilotriacetic Acid-Buffered Nutrient Solution Technique (I. Zinc Ion Requirements)

The critical range of Zn2+ activity in nutrient solution required for optimum growth of barley (Hordeum vulgare L. cv Herta) was studied using the synthetic chelating agent N-(2-hydroxyethyl)ethylenedinitrilotriacetic acid to buffer micronutrient metal ions. The activity of Zn2+ was varied over a wide range from approximately 0.1 x 10-11 to 22 x 10-11 M Zn2+. The dry weight of barley shoots reached a maximum at Zn2+ activities above approximately 3 x 10-11 M and was clearly depressed when Zn2+ activities were below about 1 x 10-11 M. The relationship in shoots between dry weight and Zn concentrations supports the view that there is a critical Zn concentration of about 25 [mu]g g-1 dry weight in whole shoots of barley seedlings. When Zn2+ activities in solution were near or below approximately 3 x 10-11 M, barley shoots accumulated higher concentrations of P, Mn, Ca, Mg, and Na, whereas Cu concentrations were reduced. P and Mn began to accumulate in the shoots before differences in dry weights were apparent and provided the earliest index of Zn deficiency. In Zn-deficient roots, concentrations of Ca and Mg increased by 25 to 30%, and those of Fe and Mn more than doubled. Zn appears to play a special role in regulating uptake of several mineral nutrients in barley.     

Conformational changes of DNA by photoirradiation of DNA-bis(Zn(II)-cyclen)-azobenzene complex

Bis(Zn(II)-cyclen)-azobenzene derivative, which has two Zn(II)-macrocyclic tetraamine complexes connected through azobenzene spacer, has been synthesized as a cross-linking agent fordoublestranded DNA in aqueous solution. The Zn(II)-cyclen derivative selectively binds to A-T base pairs producing complexes between the Zn(II)-cyclen moiety and the imide-deprotonated thymine with breaking A-T base pairs. The azobenzene spacer undergoes cis/trans photoisomerization in the complex between the Zn(II)-cyclen derivative and the DNA duplex. The conformation of the DNA remarkably changed by photoisomerization of the azobenzene linker, when the Zn(II)-cyclen derivative binds to the DNA duplex with an interstrand cross-linking manner     

Structural transition from the random coil to quadruplex of AG(3)(T(2)AG(3))(3) induced by Zn(2+)

Structures of G-quadruplex DNAs can be typically stabilized by monovalent cations such as K(+), Na(+). Some divalent and trivalent cations, such as Sr(2+), Pb(2+), Tb(3+) and Eu(3+), can also induce the formation of G-quadruplex DNA. Here we show that Zn(2+) can induce the human telomeric sequence AG(3)(T(2)AG(3))(3) to fold the G-quadruplex structure by UV absorbance difference spectra and circular dichroism (CD) spectroscopy. At micromolar concentrations, the Zn(2+)-induced changes in the UV absorbance difference spectra and CD spectra are the characteristics of antiparallel G-quadruplexes although the long wavelength CD maximum is around 285 nm rather than the typical value of 295 nm. The binding stoichometry of Zn(2+) per one AG(3)(T(2)AG(3))(3) molecule is four. To our knowledge, the structural transition of human telomeric sequence induced by Zn(2+) was observed for the first time.     

Adaptive and cross resistance to cadmium (II) and zinc (II) by Pseudomonas aeruginosa BC15

Cadmium and zinc appear in the combined forms and they are co-pollutants. Cd is the most hazardous metal ion for human beings and causes renal dysfunction, liver and lungs damage, bone degeneration and blood damage. Though Zn is an essential nutrient, excess of Zn is toxic. Biological process was more important because conventional methods fail to remediate these pollutants due to high costs and less affordability. The screening and understanding of the functioning of microorganism plays an important role in removal and recovery of metals from heavy-metal-polluted water and soil. In our study, the strain Pseudomonas aeruginosa BC15 was isolated from oil-mill-treated waste water and it showed to be highly resistant to 6 mM Cd and 20 mM Zn in the solid and liquid media. The growth studies of BC15 strain in the medium without induction exhibited high tolerable capacity when compared to other microbes. Pretreatment of P. aeruginosa BC15 with sub-lethal concentrations of Cd induced adaptive resistance to lethal doses of Cd. Cadmium-induced cells also showed cross resistance to lethal concentration of zinc. The organism had high resistance against Cd and Zn. This has been clearly proven through biosorption studies: Cd was absorbed up to 62% and Zn about 60% in single solution, whereas in binary solution Cd was biosorbed up to 82% and Zn 85%. In conclusion, this study reveals the significance of using the strain P. aeruginosa BC15 in the bioremediation of Cd and Zn from industrial waste water and contaminated soil.     

A family of insulinomimetic zinc(II) complexes of amino ligands with Zn(Nn) (n=3 and 4) coordination modes

Several metal ions and their complexes have been known to mimic the action of insulin in in vitro and in vivo systems. We prepared a family of Zn(II) complexes derived from amino ligands with Zn(Nn) (n=3 and 4) coordination modes, the insulinomimetic activity being estimated by an inhibitory effect of free fatty acid release from isolated rat adipocytes treated with epinephrine. In comparison with the positive controls VOSO(4) and ZnSO(4), Zn(II)-amine complexes with stability constants (log beta) lower than 11.5 exhibited higher insulinomimetic activities. Among them, a bis(2-aminomethyl pyridinato)Zn(II) (Zn(2-ampy)(2)(2+)) complex with the highest insulinomimetic activity and a higher stability constant but lower than 11.5 was selected, and subjected to in vivo evaluation in KK-A(y) mice with a genetically type 2 diabetes mellitus. The high blood glucose level of the mice was lowered by daily intraperitoneal injections of Zn(2-ampy)(2)(2+) at a dose of 2 mg Zn/kg body weight for 14 days. Based on the results, Zn(2-ampy)(2)(2+) with Zn(N(4)) coordination mode was proposed to have both a high in vitro insulinomimetic activity and an in vivo blood glucose lowering effect.     

Unusual dimeric Zn(II)-cytosine complexes: new models of the interaction of Zn(II) with DNA and RNA

Synthesis and crystal structure of two Zn(II) dimer complexes with 1-methylcytosine (1-MeC) are reported. In complex [Zn(2)Cl(4)(mu-1-MeC-O2,N3)(2)] (1), two 1-MeC ligands are bridging two ZnCl(2) moieties. In [Zn(2)(1-MeC-N3)(4)(mu-SO(4))(2)].2H(2)O (2), the sulfates act as bridging ligands and 1-MeC are linked via N3 to Zn(II) as terminal ligands. Both complexes represent the first examples of Zn(II)-pyrimidine dimers. The potential biological significance of 1 and 2 is discussed.