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PubMed2005

Synthesis and binding properties of hybrid cyclophane-azamacrocyclic receptors.

Three new azamacrocyclic-cyclophane hybrid receptors L(1), L(2), and L(3) have been synthesized that incorporate either 1,4,7,10-tetraazacyclododecane (cyclen) or 1,4,7-triazacyclononane (tacn) unit(s) tethered via a short amidic spacer to an electron donor and a H-bonding crown ether polycycle. The crown ether is designed to act as a host toward biologically relevant guests, whereas the macrocycle can coordinate a zinc(II) or a copper(II) ion. The pK(a) of this bound water in the zinc(II) complex of L(1) and L(2) is approximately 7.5. Isothermal calorimetry experiments carried out on [ZnL(1)(L2)(OH(2))](CF(3)SO(3))(2) and [Zn(2)L(2)(OH(2))(2)](CF(3)SO(3))(4) in buffered water (pH 7.4) at 25 degrees C show that the host strongly binds a series of phosphate derivatives. In comparison, the complex [CuL(3)(OH(2))(2)](CF(3)SO(3))(2) is a poor receptor toward phosphate substrates.

Catalysis↗

PubMed2002

Cysteine-modifying agents: a possible approach for effective anticancer and antiviral drugs.

Modification of cysteine residues in proteins, due to a) the participation of the thiol moiety of this amino acid in oxido-reduction reactions, b) its ability to strongly coordinate transition metal ions, or c) its nucleophilic nature and facile reaction with electrophiles, may be critically important for the design of novel types of pharmacological agents. Application of such procedures recently led to the design of novel antivirals, mainly based on the reaction of zinc finger proteins with disulfides and related derivatives. This approach was particularly successful for developing novel antiviral agents for human immunodeficiency virus and human papilloma virus. Several new anticancer therapeutic approaches, mainly targeting tubulin, have also been reported. Thus, this unique amino acid offers very interesting possibilities for developing particularly useful pharmacological agents, which generally possess a completely different mechanism of action compared with classic agents in clinical use, thus avoiding major problems such as multidrug resistance (for antiviral and anticancer agents) or high toxicity.

Antineoplastic Agents↗

PubMed1999

Determining anomericity of the glycosidic bond in Zn(II)-diethylenetriamine-disaccharide complexes using MSn in a quadrupole ion trap.

Zinc-diethylenetriamine (Zn-dien) N-glycoside complexes of four 1,4 and four 1,6 linked disaccharides are prepared. Each reaction mixture is ionized by electrospray and the resulting species [Zn(dien)(disaccharide)-H]+ is allowed to undergo collision-induced dissociation in a quadrupole ion trap. An MS3 analysis is used to differentiate alpha versus beta anomericity of the glycosidic bond in the disaccharide moiety. In addition, the MS2 and MS3 spectra can be used together to determine the linkage position of this glycosidic bond.

Disaccharides↗

PubMed1985

Investigation of the effect of metal ions on the reactivity of thiol groups in human 5-aminolaevulinate dehydratase.

The reaction of human 5-aminolaevulinate dehydratase with 5,5'-dithiobis-(2-nitrobenzoic acid) (Nbs2) results in the release of 4 molar equivalents of 5-mercapto-2-nitrobenzoic acid (Nbs) per subunit. Two of the thiol groups reacted very rapidly (groups I and II), and their rate constants were determined by stopped-flow spectrophotometry; the other two thiol groups (groups III and IV) were observed by conventional spectroscopy. Titration of the enzyme with a 1 molar equivalent concentration of Nbs2 resulted in the release of 2 molar equivalents of Nbs and the concomitant formation of an intramolecular disulphide bond between groups I and II. Removal of zinc from the holoenzyme increased the reactivity of groups I and II without significantly affecting the rate of reaction of the other groups. The reactions of the thiol groups in both the holoenzyme and apoenzyme were little affected by the presence of Pb2+ ions at concentrations that strongly inhibit the enzyme, suggesting that Zn2+ and Pb2+ ions may have independent binding sites. Protein fluorescence studies with Pb2+ and Zn2+ have shown that the binding of both metal ions results in perturbation of the protein fluorescence.

Apoenzymes↗

PubMed1997

Human placenta cytidine deaminase: a zinc metalloprotein.

Cytidine deaminase, a tetrameric enzyme purified from human placenta, was shown to contain a single atom of tightly bound zinc per subunit by Inductively Coupled Plasma Optical Emission Spectrometry analysis. The metal appears to be involved in catalysis, as suggested by the inhibition exerted by 1,10-phenanthroline and dipicolinic acid. This hypothesis is further supported by the finding that the presence of substrate protects the enzymatic activity from dipicolinic acid inhibition. Furthermore the total cysteine residues per subunit were investigated by sulphydryl groups titrating agents.

Amino Acid Sequence↗

PubMed2003

Voltammetric and electrochemical quartz crystal microbalance studies of sulforaphane and its Zn(II) complexes.

Cyclic voltammetry (CV) and electrochemical quartz crystal microbalance (EQCM) methods were used to study the behavior of sulforaphane (SFR). To established electrochemical properties of SFR methyl-, ethyl-, 2-chloroethyl-, propyl-, butyl- and tert-butyl-isothiocyanates were examined at gold electrode. Optimal measurement parameters were established and stock solutions developed. The electrode activity of the studied compounds (cathodic peak E(p)=-0.6 V) was found to be primarily due to the oxidation of the isothiocyanate group. By the EQCM method it was found that during the reduction of SFR the mass of the electrode systematically increased in successive scans by ca. 120 ng per scan and in the mixture of SFR and Zn(2+) ions ca. 350 ng. Formation of SFR complexes with Zn(2+) ions was confirmed by EQCM and UV methods. Cyclic voltammetric method has been elaborated for SFR determination and compared with UV method.

Electrochemistry↗

PubMed2005

Zinc trimethylsilylamide as a mild ammonia equivalent and base for the amination of aryl halides and triflates.

[reaction: see text] We report that Zn[N(SiMe(3))(2)](2) is a mild ammonia equivalent and base for the palladium-catalyzed amination of aryl halides and triflates. In contrast to LiN(SiMe(3))(2), the combination of Zn[N(SiMe(3))(2)](2) and LiCl coupled with aryl halides and triflates containing base-sensitive functionality in high yields. In addition, aryl bromides coupled with aryl and alkylamines with the combination of Zn[N(SiMe(3))(2)](2) and LiCl as base. These aminations occurred without racemization of the enolizable stereocenter of an optically active ester.

Amination↗

PubMed1977

An improved method for measuring blood mercaptans.

An improved method for measuring MT in the blood is described which uses zinc as a reducing agent and utilizes a more sensitive gas chromatograph. The method measures covalently bound MT that was not previously detected and permits determinations in patients for the first time. The average normal whole blood MT in rat blood was 200 +/- 42 pmol/ml and in human blood 229 +/- 29 pmol/ml. Eleven rats in experimental hepatic coma following acute massive hepatic necrosis had blood levels four to 18 times the average normal, and seven cirrhotic patients with hepatic encephalopathy or coma had blood levels four to five times the average normal.

Animals↗

PubMed2002

Crystal structures of leukotriene A4 hydrolase in complex with captopril and two competitive tight-binding inhibitors.

Leukotriene (LT) A4 hydrolase/aminopeptidase is a bifunctional zinc enzyme that catalyzes the final step in the biosynthesis of LTB4, a potent chemoattractant and immune modulating lipid mediator. Here, we report a high-resolution crystal structure of LTA4 hydrolase in complex with captopril, a classical inhibitor of the zinc peptidase angiotensin-converting enzyme. Captopril makes few interactions with the protein, but its free thiol group is bound to the zinc, apparently accounting for most of its inhibitory action on LTA4 hydrolase. In addition, we have determined the structures of LTA4 hydrolase in complex with two selective tight-binding inhibitors, a thioamine and a hydroxamic acid. Their common benzyloxyphenyl tail, designed to mimic the carbon backbone of LTA4, binds into a narrow hydrophobic cavity in the protein. The free hydroxyl group of the hydroxamic acid makes a suboptimal, monodentate complex with the zinc, and strategies for improved inhibitor design can be deduced from the structure. Taken together, the three crystal structures provide the molecular basis for the divergent pharmacological profiles of LTA4 hydrolase inhibitors. Moreover, they help define the binding pocket for the fatty acid-derived epoxide LTA4 as well as the subsites for a tripeptide substrate, which in turn have important implications for the molecular mechanisms of enzyme catalyses.

Amines↗

PubMed2006

{Bis(3,5-Di-tert-butyl-2-oxidobenzyl)[2-(N,N-dimethylamino)ethyl]amine-kappa(4)N,N',O,O'}zinc(II) and {bis(3-tert-butyl-5-methyl-2-oxidobenzyl)[2-(N,N-dimethylamino)ethyl]amine-kappa(4)N,N',O,O'}(tetrahdyrofuran)zinc(II).

The title zinc(II) complexes, [Zn(C(34)H(54)N(2)O(2))], (II), and [Zn(C(28)H(42)N(2)O(2))(C(4)H(8)O)], (III), were obtained as monomeric 1:1 complexes, in contrast with the calcium complexes supported by the same ligand class. Complex (II) crystallizes with two independent molecules in the asymmetric unit, which have similar geometric parameters. The donor atoms in (II) form a distorted trigonal-pyramidal arrangement around the zinc centre. Complex (III) contains a coordinated tetrahydrofuran molecule, resulting in a five-coordinate trigonal-bipyramidal arrangement around the Zn atom. The electron density provided by the coordination of this tetrahydrofuran molecule elongates the Zn-O and Zn-N bonds by approximately 0.07 and 0.10 A, respectively, in comparison with (II). Neither (II) nor (III) is active as an epsilon-caprolactone polymerization catalyst. The data presented here demonstrate that Zn may bind both an ONNO ligand and an additional oxygen-based ligand. The lack of activity is thus not due to steric hinderance at the metal atom.

Calcium↗

PubMed1986

Inhibition by FOY of kininase II in human plasma.

In this investigation we studied the inhibitory effect of FOY S 983 (gabexate mesilate) and FOY S 980 (camostate mesilate) on the kininase II activity in human plasma in vitro. Both compounds were able to inhibit kinase II, however, compared to captopril or EDTA only very weakly. The inhibitory effect of FOY S 983 or FOY S 980 could be diminished neither by NaOH-induced hydrolysis of the inhibitor nor by dialysis or ultrafiltration, but could be clearly reduced by dialysis against ZnCl2 solution. The inhibition of kininase II activity in human plasma by FOY S 983 was due to its 6-guanidinocaproate component probably acting as Zn2+-complexing agent. The ethyl 4-hydroxybenzoate component of FOY S 983 had no inhibitory effect.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed2003

[Electronic spectra and photooxidation characteristics of diimine-mixed ligand, complexes of nickel(II), copper(II) and zinc(II)].

The electronic absorption spectra of complexes M(mnt) (5-NO2-phen)(M = Ni(II), Cu(II) and Zn(II); mnt2- = 1, 2-dicyano-1, 2-ethylenedithiolate or maleonitriledithiolate; 5-NO2-phen = 5-nitro-1, 10-phenanthroline) in DMSO, DMF, DME, C2H5OH, THF, CH3CN and CH2Cl2 were reported. The relation between electronic spectral absorption band and the correlative transition in the molecular orbital energy level diagram of the complex was investigated. The essential characteristics of interligand charge transfer transition (LL'CT), and the relation between LL'CT and central metal ion, configuration, substituent electronic effect of ligands of the complexes and solvent effect were discussed. The photooxidation characteristics of complexes of M(mnt)(5-NO2-phen) in DMSO were ascertained.

Chelating Agents↗

PubMed2005

S100A9 deficiency alters adenosine-5'-triphosphate induced calcium signalling but does not generally interfere with calcium and zinc homeostasis in murine neutrophils.

The two calcium- and zinc-binding proteins, S100A9 and S100 A8, abundant in myeloid cells are considered to play important roles in both calcium signalling and zinc homeostasis. Polymorphonuclear neutrophils from S100A9 ko mice are also devoid of S100A8. Therefore, S100A9-deficient neutrophils were used as a model to study the role of the two S100 proteins in the neutrophils's calcium and zinc metabolism. Analysis of the intracellular zinc level upon pyrithione and (+/-)-(E)-methyl-2-[(E)-hydroxyimino]-5-nitro-6-methoxy-3-hexeneamide (NOR-1) treatment revealed no differences between S100A9-deficient and wildtype neutrophils. Similar, the calcium signals were not distinguishable from S100A9-deficient and wildtype neutrophils upon stimulation with platelet activating factor (PAF), thapsigargin or macrophage inflammatory protein 1 alpha (MIP-1 alpha), indicating despite their massive expression S100A8/A9 do neither serve as calcium nor as zinc buffering proteins in granulocytes. In contrast, stimulation with adenosine-5'-triphosphate (ATP) induces a significant stronger increase of the intracellular free calcium level in S100A9-deficient cells compared to wildtype cells. Moreover, the ATP-induced calcium signal was still different when the cells were incubated in calcium free buffer suggesting that pirinergic receptors of the P(2Y) class could be involved in this signalling pathway.

Adenosine Triphosphate↗

PubMed2001

Single crystal EPR and optical studies of paramagnetic ions doped zinc potassium phosphate hexahydrate--part I: Cu(II)--a case of orthorhombic symmetry.

Single crystal electron paramagnetic resonance (EPR) studies on Cu(II) doped zinc potassium phosphate hexahydrate (ZPPH) were carried out at room temperature. The angular variation spectra in the three orthogonal planes indicate that the paramagnetic impurity has entered the lattice substitutionally in place of Zn(II) and the spin Hamiltonian parameters calculated from these spectra are g(xx) = 2.188, g(yy) = 2.032, g(zz) = 2.373, Axx = 50 G, Ayy = 65.0 G and Azz = 80 G. The g and A tensors were coincident and these values matched fairly well with the values obtained from powder spectrum. The bonding parameters have also been calculated.

Copper↗

PubMed1986

Dihydroorotase from Escherichia coli. Sulfhydryl group-metal ion interactions.

We have obtained 53 mg of 99% pure dihydroorotase from 10.9 g of frozen Escherichia coli pyrC plasmid-containing E. coli cells using a 4-step 16-fold purification procedure, a yield of 60%. We characterize the enzyme by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (a dimer of subunit molecular weight 38,300 +/- 2,900), high performance liquid chromatography gel sieving, amino acid analysis, amino terminus determination (blocked), and specific activity. The isolated enzyme contains 1 tightly bound essential zinc atom/subunit, and readily but loosely binds 2 additional Zn(II) or Co(II) ions/subunit which modulate catalytic activity; treatment of crude extracts with weak chelators suggests that the enzyme contains 3 zinc atoms/subunit in vivo. Two of the 6 thiol groups/subunit react rapidly with 5,5'-dithiobis(2-nitrobenzoate) when 1 Zn/subunit enzyme is used, but slowly when 3 Zn/subunit enzyme is used. The 2 weakly bound Zn(II) ions/subunit protect against the reversible air oxidation which lowers the specific activity of the enzyme and renders it unreactive with 5,5'-dithiobis(2-nitrobenzoate). The dilution activation observed in the presence of substrate, the dilution inactivation observed in the absence of substrate, and the transient activation by the metal chelator oxalate are interpreted as evidence for an unstable, hyperactive monomer.

Amidohydrolases↗

PubMed1984

Detection of nitro-polycyclic aromatic hydrocarbons in liquid chromatography by zinc reduction and peroxyoxalate chemiluminescence.

Detection limits in the range 0.25-8.5 pg have been obtained for nitro-polycyclic aromatic hydrocarbons (nitro-PAHs) in high-performance liquid chromatography (HPLC). The nitro-PAHs are reduced on-line to the corresponding amino-PAHs and detected by peroxyoxalate chemiluminescence. Quantitative reduction is achieved on a short (3.5 X 0.32 cm) column packed with a 1:1 mixture of glass beads (ca. 40 micron) and zinc particles (40-80 micron). The mobile phase consists of 70-80% acetonitrile, the balance being a 50-mM tris(hydroxymethyl)aminomethane hydrochloride (pH 6.5) buffer, which is necessary both for the reduction and for catalysis of the chemiluminescent reaction. The amino-PAHs are excited by energy transfer from the decomposition products of the reaction between hydrogen peroxide and bis(2,4,6-trichlorophenyl)oxalate. These reagents are introduced by post-column mixing, and the emission is detected by means of a conventional fluorescence detector with its light source turned off. We reported the high sensitivity and selectivity of peroxyoxalate chemiluminescence toward amino-PAHs in earlier work. The method yields a linear response over at least three orders of magnitude, and in most cases the detection limits are better than those obtained by fluorescence detection with the same fluorometer. The reduction column may be placed either before or after the analytical column, so that the analytes are eluted either as the nitro-PAHs or the corresponding amino-PAHs. This feature provides a second characteristic retention time and is useful in identifying the detected compounds. The technique has been applied to the selective detection of nitro-PAHs in carbon black. The carbon black samples were Soxhlet extracted with toluene, evaporated to dryness, and the extracts redissolved in methylene chloride for direct injection into the HPLC column. The principal compounds found in the carbon black samples were poly-substituted nitro-PAHs and unsubstituted PAHs. This method provides a sensitive and selective method for the analysis of complex samples for these environmentally important mutagens.

Chromatography, High Pressure Liquid↗

PubMed2000

Introduction of a specific binding domain on myoglobin surface by new chemical modification.

A new myoglobin, reconstituted with a modified zinc protoporphyrin, having a total of four ammonium groups at the terminal of the two propionate side chains was constructed to introduce a substrate binding site. The protein with a positively charged patch on the surface formed a stable complex with negatively charged substrates, such as hexacyanoferrate(III) and anthraquinonesulfonate via an electrostatic interaction. The complexation was monitored by fluorescence quenching due to singlet electron transfer from the photoexcited reconstituted zinc myoglobin to the substrates. The binding properties were evaluated by Stern-Volmer plots from the fluorescence quenching of the zinc myoglobin by a quencher. Particularly, anthraquinone-2,7-disulfonic acid showed a high affinity with a binding constant of 1.5 x 10(5) M(-1) in 10 mM phosphate buffer, pH 7.0. In contrast, the plots upon the addition of anthraquinone-2-sulfonic acid at different ionic strengths indicated that the complex was formed not only by an electrostatic interaction but also by a hydrophobic contact. The findings from the fluorescence studies conclude that the present system is a useful model for discussion of electron transfer via non-covalently linked donor-acceptor pairing on the protein surface.

Anthraquinones↗

PubMed2004

Single crystal EPR studies of paramagnetic ions doped zinc potassium phosphate hexahydrate; Part III: Mn(II)-a case of rhombic distortion.

Single crystal electron paramagnetic resonance (EPR) studies of Mn(II) doped zinc potassium phosphate hexahydrate have been carried out at room temperature. Single crystal rotations along the three orthogonal axes indicate orthorhombic symmetry with spin-Hamiltonian parameters as: g(xx) = 1.9997; g(yy) = 1.9538; g(zz) = 1.9524, D(xx) = 15.49 mT; D(yy) = 0.22 mT; D(zz) = -15.71 mT, A(xx) = 11.70 mT; A(yy) = 10.53 mT; A(zz) = 10.42 mT and a = 0.8 x 10(-4) cm(-1). A large E term indicates considerable distortion from axial symmetry. The impurity is found to enter the lattice substitutionally. The distortion axis for the impurity has been identified along one of the Zn-O bond directions in the crystal.

Electron Spin Resonance Spectroscopy↗