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PubMed2007

Denitrification in a binary culture and thiocyanate metabolism in Thiohalophilus thiocyanoxidans gen. nov. sp. nov. - a moderately halophilic chemolithoautotrophic sulfur-oxidizing Gammaproteobacterium from hypersaline lakes.

Anaerobic enrichment culture with thiocyanate as electron donor and nitrate as electron acceptor at 2 M NaCl inoculated with a mixture of sediments from hypersaline lakes in Kulunda Steppe (Altai, Russia) resulted in a selection of a binary consortium of moderately halophilic, obligately chemolithoautotrophic sulfur-oxidizing bacteria (SOB) capable of complete denitrification of nitrate with thiosulfate as the electron donor. One consortium member, strain HRhD 3sp, was isolated into pure culture with nitrate and thiosulfate using a density gradient. This strain was responsible for the reduction of nitrate to nitrite in the consortium, while a second strain, HRhD 2, isolated under microoxic conditions with thiosulfate as substrate, was capable of anaerobic growth with nitrite and thiosulfate. Nitrite, either as substrate or as product, was already toxic at very low concentrations for both strains. As a result, optimal growth under anaerobic conditions could only be achieved within the consortium. On the basis of phylogenetic analysis, both organisms were identified as new lineages within the Gammaproteobacteria. As well as thiosulfate, strain HRhD 2 can also use thiocyanate as electron donor, representing a first halophilic SOB capable of growth with thiocyanate at 2-4 M NaCl. Product and enzymatic analysis identified the "carbonyl sulfide (COS) pathway" of primary thiocyanate degradation in this new species. On the basis of phenotypic and genetic analysis, strain HRhD 2 is proposed to be assigned to a new genus and species Thiohalophilus thiocyanoxidans.

Aerobiosis↗
PubMed2006

Glucosinolate hydrolysis in Lepidium sativum--identification of the thiocyanate-forming protein.

Glucosinolates are a class of thioglycosides found predominantly in plants of the order Brassicales whose function in anti-herbivore defense has been attributed to the products formed by myrosinase-catalyzed hydrolysis upon plant tissue damage. The most common type of hydrolysis products, the isothiocyanates, are toxic to a wide range of organisms. Depending on the glucosinolate side-chain structure and the presence of certain protein factors, other types of hydrolysis products, such as simple nitriles, epithionitriles and organic thiocyanates, can be formed whose biological functions are not well understood. Of the proteins controlling glucosinolate hydrolysis, only epithiospecifier proteins (ESPs) that promote the formation of simple nitriles and epithionitriles have been identified on a molecular level. We investigated glucosinolate hydrolysis in Lepidium sativum and identified a thiocyanate-forming protein (TFP) that shares 63-68% amino acid sequence identity with known ESPs and up to 55% identity with myrosinase-binding proteins from Arabidopsis thaliana, but differs from ESPs in its biochemistry. TFP does not only catalyze thiocyanate and simple nitrile formation from benzylglucosinolate but also the formation of simple nitriles and epithionitriles from aliphatic glucosinolates. Analyses of glucosinolate hydrolysis products in L. sativum autolysates and TFP transcript accumulation revealed an organ-specific regulation of thiocyanate formation. The identification of TFP defines a new family of proteins that control glucosinolate hydrolysis and challenges the previously proposed reaction mechanism of epithionitrile formation. As a protein that promotes the formation of a wide variety of hydrolysis products, its identification provides an important tool for further elucidating the mechanisms of glucosinolate hydrolysis as well as the ecological role and the evolutionary origin of the glucosinolate-myrosinase system.

Amino Acid Sequence↗
PubMed1987

The sensitivity of gamma-aminobutyric acid antagonists to thiocyanate is related to the absence of a functional anionic group in their structure.

Pyridazinyl derivatives of gamma-aminobutyric acid (GABA) have recently been shown to be selective, reversible and competitive GABAA antagonists. Unlike what is observed with all other GABAA antagonists, the affinity of these compounds for the GABAA receptor is not modified by thiocyanate. The chemical structure of these pyridazinyl-GABA derivatives differs from that of other GABAA antagonists by the presence of a free carboxylic group in their structure. We speculated that this could explain their lack of sensitivity to thiocyanate. Consequently, we synthesized three structural analogues of these pyridazinyl-GABA derivatives in which we replaced the free carboxyl group by a cyano group. These compounds displaced [3H]GABA from rat brain membranes and reversed the GABA-induced enhancement of [3H]diazepam binding. However their affinity for the GABAA receptor increased 10- to 20-fold in the presence of thiocyanate. Thus, sensitivity to thiocyanate appears to be related more to the absence of an anionic functional group than to the agonist or antagonist nature of the GABAA ligand.

Animals↗
PubMed1988

Thiocyanate stabilizes AMPA binding to the quisqualate receptor.

Calcium and chloride ions stimulated [3H]glutamate binding to quisqualate-sensitive [3H]glutamate binding sites 4-fold, as measured by quantitative autoradiography, whereas 100 mM potassium thiocyanate had no additional effect. In contrast, calcium and chloride had little effect on the binding of [3H](RS)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid ([3H]AMPA), but 100 mM thiocyanate stimulated binding 4-fold. AMPA displaced little [3H]glutamate binding from quisqualate-sensitive binding sites in the molecular layer of the cerebellum in the absence of thiocyanate. However, in the presence of thiocyanate AMPA became a more effective displacer, but still displaced only 44% of the quisqualate-sensitive [3H]glutamate binding. The distribution of [3H]glutamate binding to quisqualate-sensitive sites was similar to but not identical with that of [3H]AMPA binding. However, the distribution of AMPA-displaceable [3H]glutamate binding correlated highly (r = 0.97, P less than 0.0005) with that of [3H]AMPA binding. The results suggest that AMPA binds to a subclass of quisqualate-sensitive [3H]glutamate binding sites that are highly influenced by ionic environment and that quisqualate-sensitive binding sites exist in several states.

Animals↗
PubMed1993

NMR relaxation studies of the interaction of thiocyanate with lactoperoxidase.

The interaction of lactoperoxidase, LPO, with its substrate, thiocyanate, SCN-, has been investigated by 13C and 15N NMR relaxation measurements. When 0.1 M SCN-, enriched with either 13C or 15N, was titrated with native ferric lactoperoxidase a large change in the spin-lattice relaxation time of the respective nucleus was observed. In the presence of saturating amounts of CN-, a high affinity ligand for the heme iron, a similar but much smaller change in the relaxation time for SCN- was found. Studies of the rate of carbon relaxation as a function of temperature have shown that thiocyanate is in fast exchange between a site on the enzyme and bulk solution. When LPO in either the absence or presence of CN- was titrated with SCN- a linear increase in the relaxation time was observed. Dissociation constants (Kd values) have been determined from a least-squares analysis of these data. Apparent distances between the heme iron of lactoperoxidase and either the carbon or nitrogen atoms of bound thiocyanate ion have been determined through application of the Solomon-Bloembergen equation. These distances demonstrate that the observed association does not involve iron-thiocyanate coordination, suggesting the possibility of an anion binding site.

Animals↗
PubMed1995

Opposing placental gradients for thiocyanate and cotinine at birth.

In order to compare maternal and fetal exposure to compounds of tobacco smoke at the end of pregnancy, concentrations of cotinine and thiocyanate were measured in cord serum and maternal serum collected from 24 daily smoking and four non-smoking women at the time of child birth. The median level of thiocyanate (69 mumol/l) in maternal serum was about 50% higher than the median level (47 mumol/l) in cord serum (P < 0.0001) (Wilcoxon matched-pairs signed-ranks test). On the other hand, the median level of cotinine (22 ng/ml) in maternal serum was less than half of the median level (51 ng/ml) in cord serum (P = 0.0009). The correlation between maternal and cord serum was 0.77 (P < 0.0001) (Spearman's rank correlation coefficient) for thiocyanate levels and 0.90 (P < 0.0001) for cotinine. The high correlation between measurements of cotinine in maternal serum and cord serum indicates that maternal cotinine levels can be used to describe interindividual differences in fetal exposure to tobacco smoke. The placental gradients for cotinine and thiocyanate may indicate differences in maternal and fetal exposure to products of tobacco smoke.

Adult↗
PubMed2005

Kinetic studies of adsorption of thiocyanate onto ZnCl2 activated carbon from coir pith, an agricultural solid waste.

The adsorption of thiocyanate onto ZnCl2 activated carbon developed from coir pith was investigated to assess the possible use of this adsorbent. The influence of various parameters such as agitation time, thiocyanate concentration, adsorbent dose, pH and temperature has been studied. Adsorption followed second-order rate kinetics. Two theoretical adsorption isotherms, namely, Langmuir and Freundlich were used to describe the experimental results. The Langmuir adsorption capacity (Q0) was found to be 16.2 mg g(-1) of the adsorbent. The per cent adsorption was maximum in the pH range 3.0-7.0. pH effect and desorption studies showed that ion exchange and chemisorption mechanism are involved in the adsorption process. Thermodynamic parameters such as DeltaG0, DeltaH0 and DeltaS0 for the adsorption were evaluated. The negative values of DeltaH0 confirm the exothermic nature of adsorption. Effects of foreign ions on the adsorption of thiocyanate have been investigated. Removal of thiocyanate from ground water was also tested.

Adsorption↗
PubMed2004

Unique stress response to the lactoperoxidase-thiocyanate enzyme system in Escherichia coli.

Using a differential fluorescence induction approach, we screened a promoter trap library constructed in a vector with a promoterless gfp gene for Escherichia coli MG1655 promoters that are induced upon challenge with the antimicrobial lactoperoxidase-thiocyanate enzyme system. None of the thirteen identified lactoperoxidase-inducible open reading frames was inducible by H(2)O(2) or by the superoxide generator plumbagin. However, analysis of specific promoters of known stress genes showed some of these, including recA, dnaK and sodA, to be inducible by the lactoperoxidase-thiocyanate enzyme system. The results show that the lactoperoxidase-thiocyanate enzyme system elicits a distinct stress response different from but partly overlapping other oxidative stress responses. Several of the induced genes or pathways may be involved in bacterial defense against the toxic effects of the lactoperoxidase-thiocyanate enzyme system.

Escherichia coli↗
PubMed1977

Determination of thiocyanate in tissues and body fluids of animals by gas chromatography with electron-capture detection.

A method for the quantitative extraction of thiocyanate from biological material has been developed. Levels of 0.2-5 ppm of thiocyanate, in the presence of cyanide, were determined by gas-solid chromatography using 2-bromopropane as internal standard. Reliable results can be obtained only after careful deproteinization of the extracts with hot methanol. Cyanide can be eliminated by reaction with alkaline formaldehyde. The reproducibility of the determination of thiocyanate in biological extracts was +/-5%; the recoveries were over 90%. In vivo experiments with KS14CN-treated rats gave good agreement between the analytical results and the amount of thiocyanate determined by isotope dilution.

Animals↗
PubMed1984

Determination of cyanide and thiocyanate in blood plasma and red cells by high-performance liquid chromatography with fluorometric detection.

A method for the determination of cyanide and thiocyanate in blood plasma and red cells of humans was established. It involved high-performance liquid chromatography and fluorometric detection by the König reaction. Calibration curves for cyanide and thiocyanate were linear in the range 1-200 pmol and 2-300 pmol, respectively. Clean-up methods for the determination of cyanide and thiocyanate in red cells were also developed. These methods were applied for the determination of cyanide and thiocyanate in the blood of smokers and non-smokers.

Ascorbic Acid↗
PubMed1995

X-ray crystallographic studies on hexameric insulins in the presence of helix-stabilizing agents, thiocyanate, methylparaben, and phenol.

Three X-ray crystallographic studies have been carried out on pig insulin in the presence of three ligands, thiocyanate, methylparaben (methyl p-hydroxybenzoate), and phenol. In each case, rhombohedral crystals were obtained, which diffracted to 1.8, 1.9, and 2.3 A, respectively. Each crystal structure was very similar to that of 4-zinc pig insulin, which was used as a starting model for PROLSQ refinement (Collaborative Computational Project, Number 4, 1994). The R factors for the refined structures of thiocyanate insulin, methylparaben insulin, and phenol insulin were 19.6, 18.4, and 19.1, respectively. Each crystal structure consists of T3R3f insulin hexamers with two zinc ions per hexamer. In the R3f trimer of the thiocyanate insulin hexamer, one thiocyanate ion is coordinated to the zinc on the hexamer 3-fold axis, but there is no evidence of zinc ion binding in the off-axis zinc ion sites seen in the 4-zinc pig insulin structure. In the methylparaben insulin and phenol insulin hexamers, the phenolic ligands are bound at the dimer-dimer interfaces in the R3f trimers in a manner similar to that of phenol in R6 phenol insulin. The binding of methylparaben appears to make the hexamer more compact by drawing the A and the B chains closer together in the binding site. In all three structures presented herein, the conformations of the first three residues of the B chain in the R3f trimer are extended rather than alpha-helical, as is seen in R6 phenol insulin. The energetics of ligand binding in the insulin hexamer are discussed.

Animals↗
PubMed2003

A unique autocatalytic process and evidence for a concerted-stepwise mechanism transition in the dissociative electron-transfer reduction of aryl thiocyanates.

Electrochemical reduction of p-methyl-, p-methoxy-, and 3,5-dinitrophenyl thiocyanates as well as p-methyl- and p-methoxyphenyl disulfides was investigated in acetonitrile at an inert electrode. This series of compounds reveals a striking change in the reductive cleavage mechanism of the S-CN bond in thiocyanates as a function of the substituent on the aryl ring of the aryl thiocyanate. With nitro substituents, a stepwise mechanism, with an anion radical as the intermediate, takes place. When electron-donating groups (methyl and methoxy) are present, voltammetric as well as convolution analyses provide clear evidence for a transition between the concerted and stepwise mechanisms based on the magnitude of the transfer coefficient alpha. Moreover, a very interesting autocatalytic process is involved during the electrochemical reduction of these compounds. This process involves a nucleophilic substitution reaction on the initial aryl thiocyanate by the electrochemically generated arenethiolate ion. As a result of this unusual process, the electrochemical characteristics (peak potential and peak width) of the investigated series are concentration dependent.

Benzene Derivatives↗
PubMed2005

Autocatalytic modification of the prosthetic heme of horseradish but not lactoperoxidase by thiocyanate oxidation products. A role for heme-protein covalent cross-linking.

The mammalian peroxidases eosinophil peroxidase, lactoperoxidase (LPO), and myeloperoxidase oxidize thiocyanate to the antimicrobial agents hypothiocyanous acid (HOSCN) and (SCN)2 and are part of a defense system that protects the host from infections. Horseradish peroxidase (HRP), a plant enzyme, also oxidizes thiocyanate. We report here that the prosthetic heme vinyl groups of HRP react with the catalytically generated HOSCN and (SCN)2 to form at least nine vinyl-modified heme adducts. Mass spectrometry combined with analysis of the equivalent reactions of HRP reconstituted with 2- or 4-cyclopropylheme, or mesoheme-d4, shows that all of the prosthetic heme modifications result from addition of oxidized thiocyanate to the heme vinyl groups. No delta-meso-substitution of the heme was observed, in contrast to what is observed with radical agents. Model studies show that incubation of either HRP with preformed HOSCN or a solution of heme with preformed (SCN)2 gives rise to the same products obtained in the HRP-catalyzed reaction. Model studies also demonstrate that the SCN* radical, if formed, should add to a meso-carbon. These findings implicate an electrophilic addition mechanism. In contrast, oxidation by LPO of thiocyanate, the normal substrate of this enzyme, does not result in heme modification. In view of the demonstrated intrinsic reactivity of the heme group, LPO must actively suppress heme modification. As the key difference between LPO (and other mammalian peroxidases) and HRP is the presence of two covalent ester links between the heme and the protein, we propose that these links contribute to steric protection of the adjacent heme vinyl groups.

Catalysis↗
PubMed2002

Design, synthesis, and biological evaluation of aryloxyethyl thiocyanate derivatives against Trypanosoma cruzi.

As a continuation of our project aimed at the search for new and safe chemotherapeutic and chemoprophylactic agents against American trypanosomiasis (Chagas' disease), several drugs structurally related to 4-phenoxyphenoxyethyl thiocyanate (4) were designed, synthesized, and evaluated as antiproliferative agents against the parasite responsible for this disease, the hemoflagellated protozoan Trypanosoma cruzi. This thiocyanate derivative was previously shown to be an effective and potent agent against T. cruzi proliferation. Several drugs possessing thiocyanate groups proved to be effective growth inhibitors of T. cruzi growth. Among the designed compounds, it is important to point out the extremely potent activity shown by 11, 23, 38, 53, 90, 99, and 117 against the epimastigote forms of the parasite. All of them exhibited IC(50) values in the low micromolar range, and these values were comparable with those presented by our lead drug 4 and ketokonazole, a well-known antiparasitic agent. The activity displayed by the nitrogen-containing derivative 90 was very promising with IC(50) values of 3.3 microM. Several other thiocyanate derivatives also proved to be very potent inhibitors of the multiplication of T. cruzi epimastigotes, such as compounds 28, 33, 43, 48, 56, 61, 66, 71, 76, and 124. Compound 43 resulted in being a promising drug because it was also very effective against amastigotes, the clinically more relevant form of the parasite. This compound was 3-fold more potent than 4, while 11 showed nearly the same activity as our lead drug against intracellular T. cruzi. It was very surprising that the experimental juvenoid 124, although fairly devoid of activity against epimastigotes, was very effective against intracellular amastigotes growing in myoblasts. The rest of the designed compounds showed a broad degree of inhibitory action, from moderately active drugs to drugs almost devoid of antiparasitic activity. Compound 43 is an interesting example of an effective antichagasic agent that presents excellent prospectives not only as a lead drug but also to be used for further in vivo studies.

Animals↗
PubMed1998

Role of thiocyanate ion in detoxification of the anticancer agent chlorambucil.

N,N-Bis(2-chloroethyl)-p-aminophenylbutyric acid (chlorambucil, 1) is an orally administrated drug widely used in the chemotherapy of chronic lymphocytic leukemia. We have recently described a new metabolic path for the decomposition of 1 in human gastric juice based on its reactions with saliva-derived thiocyanate ion. We report here our quantitative data on the reactions of thiocyanate ion with CLB in various fluid matrixes at 37 degreesC. The rate of decomposition of 1 is zero-order with respect to SCN- concentration up to 100 mM. However, thiocyanate ion reacts ca. 18 300 times faster than water with the aziridinium ion derived from 1 at neutral and acidic pH. When the SCN- concentration was greater than 10 mM, practically no N,N-bis(2-hydroxyethyl)-p-aminophenylbutyric acid, 4, the product of chlorambucil hydrolysis, could be detected. Thiocyanate ion also effectively overcompensates for the rate retardation caused by Cl-; 10 mM SCN- is enough to decrease the effect of 0.5 M chloride ion to one-half. This is an important factor in human gastric juice where the chloride ion concentration is normally high.

Antineoplastic Agents, Alkylating↗
PubMed1998

Electrooxidation of thiocyanate on the copper-modified gold electrode and its amperometric determination by ion chromatography.

Cyclic voltammetry was used to investigate the electrochemical behavior of an Au/Cu electrode towards the electrooxidation of thiocyanate ion in alkaline medium. The effects of pH, copper loading, scan rate and applied potential on the electrocatalytic oxidation of thiocyanate have been investigated. Flow injection experiments and ion-chromatography (IC) were performed to characterise the electrode as an amperometric sensor for the thiocyanate determination. The effects of carbonate concentration and common interferents on the retention time were also estimated. The electrode stability, precision, limit of detection and linear range were evaluated at a constant applied potential of 0.7 V vs. Ag/AgCl. Calibration plots, obtained in IC, were linear from 1.0 to 195 microM (correlation coefficient of 0.9984). The detection limit (LOD) was 0.5 microM (29 ppb) in a 50 microlitres injection. An example of analytical application, which includes the IC separation and detection of thiocyanate ion present in human urine, is given.

Chromatography, Ion Exchange↗
PubMed2000

Indirect determination of thiocyanate with ammonium sulfate and ethanol by extraction-flotation of copper.

A new method for the indirect determination of thiocyanate with ammonium sulfate and ethanol by extraction-flotation of copper in the presence of ascorbic acid is described. A small amount of Cu(II) is reduced to Cu(I) by ascorbic acid, then Cu(I) is precipitated with SCN-. In the course of phase separation of ethanol from water, the precipitated CuSCN stays in the interface of ethanol and water. A good linear relationship is observed between the flotation yield of Cu(II) and the amount of SCN-. Using 1.0 ml of 1 x 10(-3) M ascorbic acid solution, 50 micrograms of Cu(II), 3.5 g of (NH4)2SO4 and 3.0 ml of ethanol with a total volume of 10 ml, the concentration of thiocyanate could then be determined by determining the flotation yield of Cu(II). The detection limit for thiocyanate is 5 x 10(-5) M. Every parameter was optimized and the reaction mechanism was studied. The method is simple and rapid and it was successfully applied to the determination of thiocyanate in urine and saliva of smokers and non-smokers and in venous blood of patients infused with sodium nitroprusside.

Ammonium Sulfate↗
PubMed2000

Mechanism of DNA damage by thiocyanate radicals.

PURPOSE: It was previously shown that gamma-irradiation of aqueous solutions of plasmid DNA in the presence of millimolar concentrations of thiocyanate ions leads to the formation in very high yields of sites recognized by the base excision repair endonuclease formamido-pyrimidine-DNA N-glycosylase (FPG). The authors wished to characterize the mechanism responsible for the production of these FPG-sensitive sites. MATERIALS AND METHODS: An aqueous solution of plasmid DNA containing thiocyanate ions was irradiated with 137Cs gamma-rays. After irradiation, aliquots were treated with FPG. Break yields were determined using neutral agarose gel electrophoresis. RESULTS: The yield of FPG-sensitive sites decreased with decreasing enzyme activity, increasing thiocyanate concentration, increasing dose-rate, increasing ionic strength, increasing nitrite or iodide concentration, and decreasing oxygen concentration. CONCLUSION: The observations suggest that the monomeric thiocyanate radical SCN* is an intermediate in the reaction, and that the yields of FPG-sensitive sites are determined by competition between the disproportionation of the dimeric radical anion (SCN)*2- and the fate of a one-electron oxidized guanine species in DNA. The latter can react with oxygen to produce an FPG-sensitive site or can be reduced without producing an FPG-sensitive site. The results help to clarify the mechanisms responsible for DNA damage by the direct effect of ionizing radiation.

DNA↗