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PubMed1988

Steady-state kinetics of thiocyanate oxidation catalyzed by human salivary peroxidase.

A steady-state kinetic analysis was made of thiocyanate (SCN-) oxidation catalyzed by human peroxidase (SPO) isolated from parotid saliva. For comparative purposes, bovine lactoperoxidase (LPO) was also studied. Both enzymes followed the classical Theorell-Chance mechanism under the initial conditions [H2O2] less than 0.2mM, [SCN-] less than 10mM, and pH greater than 6.0. The pH-independent rate constants (k1) for the formation of compound I were estimated to be 8 X 10(6) M-1 s-1 (SD = 1, n = 18) for LPO and 5 X 10(6) M-1 s-1 (SD = 1, n = 11) for SPO. The pH-independent second-order rate constants (k4) for the oxidation of thiocyanate by compound I were estimated to be 5 X 10(6) M-1 s-1 (SD = 1, n = 18) for LPO and 9 X 10(6) M-1 s-1 (SD = 2, n = 11) for SPO. Both enzymes were inhibited by SCN- at pH less than 6. The pH-independent equilibrium constant (Ki) for the formation of the inhibited enzyme-SCN- complex was estimated to be 24 M-1 (SD = 12, n = 8) for LPO and 44 M-1 (SD = 4, n = 10) for SPO. An apparent pH dependence of the estimated values for k4 and Ki for both LPO and SPO was consistent with a mechanism based on assumptions that protonation of compound I was necessary for the SCN- peroxidation step, that a second protonation of compound I gave an inactive form, and that the inhibited enzyme-SCN- complex could be further protonated to give another inactive form.(ABSTRACT TRUNCATED AT 250 WORDS)

Humans↗
PubMed2002

Reaction of lactoperoxidase compound I with halides and thiocyanate.

Lactoperoxidase (LPO) is found in mucosal surfaces and exocrine secretions, including milk, tears, and saliva, and has physiological significance in antimicrobial defense which involves (pseudo-) halide oxidation. This study for the first time presents transient kinetic measurements of the reactivity of its competent redox intermediate compound I with halides and thiocyanate, using the sequential stopped-flow technique. Compound I was produced with either H(2)O(2) [(1.1 +/- 0.1) x 10(7) M(-1) s(-1)] or hypochlorous acid [(3.2 +/- 0.1) x 10(7) M(-1) (s-1)]. At pH 7 and 15 degrees C, the two-electron reduction of compound I to native LPO by bromide and iodide has a second-order rate constant of (4.1 +/- 0.1) x 10(4) M(-1) s(-1) and (1.2 +/- 0.04) x 10(8) M(-1) s(-1), respectively. With thiocyanate the reaction is extremely fast (2.0 x 10(8) M(-1) s(-1)), whereas chloride cannot function as electron donor. The results are discussed with respect to known kinetic data of homologous mammalian peroxidases and to the physiological role of LPO in antimicrobial defense.

Animals↗
PubMed2002

Iron(VI) and iron(V) oxidation of thiocyanate.

Thiocyanate (SCN-) is used in many industrial processes and is commonly found in industrial and mining waste-waters. The removal of SCN- is required because of its toxic effects. The oxidation of thiocyanate (SCN-) by environmentally friendly oxidants, Fe(VI) and Fe(V), has been studied anaerobically using stopped-flow and premix pulse radiolysis techniques. The stoichiometry with Fe(VI) was determined to be 4HFeO(4-) + SCN(-) + 5H2O-->4Fe(OH)3 + SO4(2-) + CNO(-) + O2 + 2OH-. The rate law for the oxidation of SCN- by Fe(VI) was found to be -d[Fe(VI)]/dt = k11([H+]/([H+] + Ka,HFeO4)) [Fe(VI)][SCN-] where k11 = 2.04 +/- 0.04 x 10(3) M-1 s-1 and pKa,HFeO4 = 7.33. A mechanism is proposed that agrees with the observed reaction stoichiometry and rate law. The rate of oxidation of SCN- by Fe(V) was approximately 3 orders of magnitude faster than Fe(VI). The higher reactivity of Fe(V) with SCN- indicates that oxidations by Fe(VI) may be enhanced in the presence of appropriate one-electron-reducing agents. The results suggest that the effective removal of SCN- can be achieved by Fe(VI) and Fe(V).

Industrial Waste↗
PubMed2004

Reactive sulfur species: aqueous chemistry of sulfenyl thiocyanates.

Sulfenyl thiocyanate (RSSCN) derivatives of penicillamine (PENSCN) and glutathione (GSSCN) have been synthesized in situ at pH = 0 from equilibrium mixtures that consists of hypothiocyanous acid (HOSCN), thiocyanogen ((SCN)2), and trithiocyanate ((SCN)3-). The electrophilic thiocyanating agent N-thiocyanatosuccinimide (NTS) also reacts with PEN and GSH to yield the corresponding RSSCN derivatives. PENSCN and GSSCN were characterized by NMR, ES-MS, and IR spectroscopy. While stable at pH = 0, at higher pH the RSSCN derivatives decompose to give products that are consistent with hydrolysis and formation of reactive sulfenic acids.

Cysteine↗
PubMed2006

Site-specific conversion of cysteine thiols into thiocyanate creates an IR probe for electric fields in proteins.

The nitrile stretching mode of the thiocyanate moiety is a nearly ideal probe for measuring the local electric field arising from the organized environment of the interior of a protein. Nitriles were introduced into three proteins: ribonuclease S (RNase S), human aldose reductase (hALR2), and the reaction center (RC) of Rhodobacter capsulatus, through a facile synthetic scheme for the transformation of cysteine residues into thiocyanatoalanine. Vibrational Stark effect spectroscopy and Fourier transform infrared spectroscopy on the modified proteins demonstrated that thiocyanate residues are a highly general tool for probing electrostatic fields in proteins.

Cysteine↗
PubMed2003

The hydration structure of guanidinium and thiocyanate ions: implications for protein stability in aqueous solution.

Neutron diffraction experiments were carried out on aqueous solutions containing either guanidinium or thiocyanate ions. The first-order difference method of neutron diffraction and isotopic substitution was applied, and the hydration structures of two of nature's strongest denaturant ions were determined. Each ion is shown to interact weakly with water: Guanidinium has no recognizable hydration shell and is one of the most weakly hydrated cations yet characterized. Hydration of thiocyanate is characterized by a low coordination number involving around one hydrogen-bonded water molecule and approximately two water molecules weakly interacting through "hydration bonds." The weak hydration of these denaturant ions strongly supports suggestions that a major contribution to the denaturant effect is the preferential interaction of the denaturant with the protein surface. By contrast, solute species such as many sugars and related polyols that stabilize proteins are strongly hydrated and are thus preferentially retained in the bulk solvent and excluded from the protein surface.

Biophysical Phenomena↗
PubMed1981

Thiocyanate and hydroxyl ions inactivate the scrapie agent.

To probe the macromolecular structure of the scrapie agent and explore conditions for monomerization, the stability of the agent in low concentrations of inorganic ions was determined. A reduction by a factor of 10(5) in scrapie titer was found on exposure of the agent to 1 M KSCN or 0.3 M NaOH. In addition to the inactivation by thiocyanate ions, other chaotropic ions such as guanidinium and trichloroacetate inactivate the scrapie agent. Removal of thiocyanate ions by dialysis or glass permeation chromatography prevented the reduction in scrapie agent infectivity. Addition of equimolar amounts of (NH4)2SO4, a nonchaotrope, to preparations containing 1 M KSCN also prevented the loss of scrapie infectivity. In contrast, neutralization of the alkali-treated fractions with HCl did not restore infectivity. Acidification of partially purified fractions did not cause inactivation of the agent but did result in precipitation of the infectious agent. Inactivation by relatively low concentrations of chaotropic ions is consistent with many observations, all of which suggest that the scrapie agent contains a protein component that is essential for the maintenance of infectivity. Thus, it is unlikely that the agent is composed only of a "naked" nucleic acid. Certainly, if the agent were a naked nucleic acid, its lability in alkali virtually eliminates the possibility that it is composed of a single-stranded molecule of DNA.

Ammonium Sulfate↗
PubMed1984

Spectrophotometric determination of vanadium in complex materials using N-m-TMBHA and thiocyanate.

Vanadium(V) reacts with N-m-Tolyl-p-methoxy benzohydroxamic acid to form 1:2 (metal to ligand) complex containing a basic V = O group and an acidic V-OH group, which forms addition compounds with thiocyanate to give a hyper and bathochromic effect in chloroform. On the basis of this bathochromic effect of thiocyanate a rapid, selective and sensitive method for the spectrophotometric determination of vanadium(V) has been developed. The blue coloured complex of vanadium(V) is extractable in chloroform having absorption maxima at 580 nm and max 7100 +/- 50 1 X mole-1 cm-1. The method is free from interferences of Mo(VI), W(VI), Zr(IV) and has been successfully applied for the analysis of steels and other complex materials.

Chemical Phenomena↗
PubMed1984

Relationship of serum thiocyanate concentrations to smoking characteristics.

Thiocyanate (SCN) concentrations were determined in serum samples from 130 young healthy persons (60 smokers) and related to their smoking and physiologic characteristics. Serum thiocyanate correlated strongly and approximately equally with the number of cigarettes/d X kg of ideal body weight (IBW) (r = 0.748), total nicotine intake in mg/d X kg IBW (r = 0.735), and total tar intake in mg/d X kg IBW (r = 0.731). Multiple linear regression analysis that included these factors as well as sex, marijuana use, menthol, and degree of inhalation only increased the multiple r to 0.803. A more sensitive statistical method (NYBAID) was also used to determine the most significant influences of these variables on serum SCN. The association with depth of inhalation (i.e., smoking versus nonsmoking) was dominant among the relationships considered. The highest SCN levels were exhibited in heavy nicotine users (8.58 +/- 3.00 mg/l), while average users had slightly lower concentrations (6.49 +/- 2.37 mg/l) (p less than 0.03). In nontobacco smokers, those who smoked marijuana several times weekly had higher SCN levels (4.66 +/- 2.16 mg/l) than noncannabis users (2.38 +/- 1.38 mg/l) (p less than 0.03). These studies confirm the utility of serum SCN as an index of smoking rate and demonstrate the role of secondary variables in accounting for the chemical in serum.

Adult↗
PubMed1976

Cyanide and thiocyanate concentrations following sodium nitroprusside infusion in man.

Twenty-six patients, receiving an infusion of sodium nitroprusside (SNP) during surgery, had considerable increases in both red cell and plasma cyanide concentration, but only small changes in plasma thiocyanate concentration. There was a linear relationship between both plasma and RBC cyanide concentrations and the total dose of SNP. The expired cyanide concentration followed the changes in the plasma. We believe that the development of metabolic acidosis, and the recent fatalities involving SNP, are attributable to histotoxic hypoxia as a result of excessive plasma concentrations of cyanide. On the basis of our results, we recommend that the total dose of SNP should not exceed 1.5 mg/kg during short-term infusions and that the plasma cyanide should not exceed 300 nmol%. Plasma thiocyanate concentrations are, in general, an unreliable indication of extent of exposure to cyanide, although they may become important during long-term infusions.

Adolescent↗
PubMed1993

Modifying effects of benzyl isothiocyanate and benzyl thiocyanate on DNA synthesis in primary cultures of rat hepatocytes.

The effects of benzyl isothiocyanate (BITC) and benzyl thiocyanate (BTC) on two types of DNA synthesis were examined in hepatocyte primary cultures (HPC). Male F344 rats were fed BITC- or BTC-containing diets at a concentration of 400 p.p.m. Using hepatocytes isolated from these rats, DNA repair was measured by unscheduled DNA synthesis (UDS) for some genotoxic carcinogens, e.g. 2-acetylaminofluorene (AAF), methylazoxymethanol (MAM) acetate, 9,10-dimethyl-1,2-benzanthracene (DMBA) and diethylnitrosamine (DEN), and compared with that in the hepatocytes from rats without BITC or BTC treatment. Replicative DNA synthesis (RDS) was also evaluated in the hepatocytes of rats with or without thiocyanate treatment. Both BITC and BTC reduced UDS elicited by these carcinogens. The level of RDS in the hepatocytes of rats exposed to BITC or BTC was markedly lower than in the cells of rats without BITC or BTC exposure. These results indicate that in vivo exposure to BITC and BTC suppressed carcinogen-induced genotoxicity and cell proliferative activity and suggest that this assay may prove useful in detecting chemopreventive agents for cancer and in investigating the properties of carcinogenesis modifiers.

Animals↗
PubMed1994

Inhibitory effects of benzyl thiocyanate and benzyl isothiocyanate on methylazoxymethanol acetate-induced intestinal carcinogenesis in rats.

The effects of two aromatic thiocyanates, benzyl thiocyanate (BTC) and benzyl isothiocyanate (BITC), on methylazoxymethanol (MAM) acetate-induced intestinal carcinogenesis were examined using female ACI/N rats. Starting at 5 weeks of age, animals were fed diets containing 100 or 400 p.p.m. BTC, 400 p.p.m. BITC or a control diet. At 6 weeks of age, all animals were treated with i.p. injections of MAM acetate (25 mg/kg body wt, once weekly for 3 weeks) or saline. Animals fed experimental diets were changed to the control diet from a week after the last carcinogen treatment. Three groups of animals fed the control diet were switched to 100 p.p.m. BTC, 400 p.p.m. BTC or 400 p.p.m. BITC diet from a week after carcinogen treatment. Animals given the high-dose BTC diet at the initiation and the post-initiation phase showed smaller incidence (5% and 17%) and multiplicity (0.05 +/- 0.21 and 0.17 +/- 0.37) of tumours in small intestine compared with those of rats exposed to the carcinogen alone (61% and 1.06 +/- 1.18). The incidence and multiplicity of tumors in small intestine (21% and 0.32 +/- 0.73) and the incidence of colon tumors of rats given BITC in the initiation phase (47%) were significantly lower than those of animals treated with carcinogen alone (61%, 1.06 +/- 1.18 and 83%). Bromodeoxyuridine labeling indices of the intestinal mucosal cells were measured. The labeling indices were reduced by BTC and BITC exposure at initiation phase in both small intestine and colon. The results of measurement of labeling indices correlated with the decreased tumor incidence and multiplicity in the intestine. These data suggest that BTC and BITC could be promising chemopreventive agents for human intestinal neoplasia.

Animals↗
PubMed1996

Thiocyanate-independent nitrosation in humans with carcinogenic parasite infection.

Infection with the liver fluke, Opisthorchis viverrini, is a causative agent of cholangiocarcinoma. One possible contributing factor in this carcinogenesis is the chronic, local generation of nitric oxide by inflammatory cells expressing inducible nitric oxide synthase and the production of N-nitroso compounds via the reaction between amines and nitrosating agents derived from nitric oxide. Our previous studies provided evidence that nitric oxide synthesis is elevated during human liver fluke infection. Here we present data on the same sample of men which definitively demonstrates increased nitrosation of proline and thioproline (thiazolidine-4-carboxylic acid) among infected men compared to uninfected control subjects on a low nitrate diet. This difference was specifically abolished by co-administration of ascorbic acid with proline and by elimination of parasites by praziquantel treatment. Multivariate statistical models demonstrate the importance of salivary thiocyanate levels to variation in the nitrosation of proline among uninfected individuals, but not among those with current fluke infection. This suggests that considerable generation of nitrosating agents (N203/N204) in infected people may be occurring via oxidation of arginine by nitric oxide synthase in inflamed tissue which is thiocyanate insensitive. Analyses revealed positive associations between N-nitrosoproline excretion and nitrate/nitrite levels in urine, plasma and saliva and with usual alcohol intake; with variation in these trends between groups. In conclusion, we have confirmed the relationship between O.viverrini infection and enhanced endogenous nitrosation, showing evidence of its extragastric site. New information is also provided on the determinants of N-nitrosamino acid excretion in men on a controlled low nitrate diet without smoking, conditions which reduce exogenous sources of nitrosating agents.

Adult↗
PubMed1992

Discrimination of smoking status by thiocyanate and cotinine in serum, and carbon monoxide in expired air.

To develop a procedure for maximizing the discrimination of smoking status, the authors analysed parallel samples of thiocyanate and cotinine in serum, and carbon monoxide (CO) in expired air in a cohort of 145 male subjects aged 45-65 years. The sensitivity and specificity were 93% and 82%, 97% and 83%, and 98% and 100% for thiocyanate, cotinine, and CO respectively. The results were not significantly improved when combining two or three methods as compared with CO separately. Also, cotinine in urine was analysed in a subgroup of 21 subjects. The correlation coefficient between cotinine in serum and urine was 0.92. In a subgroup of 44 subjects with extensive information on smoking habits, CO was the only indicator significantly related to the quantity of tobacco smoked. We conclude that CO seems sufficient for validating smoking status, but as atypical smokers who are vulnerable to misclassification may be overrepresented in smoking cessation programmes, combining two methods could still be useful. Validating the amount of tobacco smoked is of limited use with the current methods.

Aged↗
PubMedDate not supplied

Determination of serum levels of dietary thiocyanate.

A spectrophotometric method was used to determine thiocyanate (SCN-) levels in human serum, in an attempt to relate serum levels of this ion to the dietary intake of vegetables of the genus Brassica. Thiocyanate ion was measured before and after a one-week period during which the subjects ate a diet rich in these vegetables. We also determined the serum increase in SCN- 2 h after the administration of 0.5 g KSCN.

Adult↗
PubMed1992

Structure determination of a dimeric form of erabutoxin-b, crystallized from a thiocyanate solution.

Erabutoxin-b, M(r) = 6861.1, a single 62 amino-acid chain folded by four disulfide bridges, was crystallized in a new orthorhombic form by using thiocyanate as crystallizing agent. The space group is P2(1)2(1)2(1) with a = 53.36 (4), b = 40.89 (4), c = 55.71 (5) A, V = 121533.1 A and Z = 8. X-ray diffraction data were recorded at the LURE synchrotron facility (lambda = 1.405 A). The structure was solved by molecular replacement and shows a dimeric association through an anti-parallel beta-sheet around the twofold non-crystallographic axis. The two independent molecules, one SCN- ion and 97 associated water molecules were refined by molecular dynamics and annealing techniques to R = 19.6% (10,913 Fobs, resolution 5-1.7 A). The thiocyanate ion is located at the interface of the dimer and close to the non-crystallographic twofold axis.

Amino Acid Sequence↗
PubMed1999

The decameric structure of bovine pancreatic trypsin inhibitor (BPTI) crystallized from thiocyanate at 2.7 A resolution.

The structure of a monoclinic form of bovine pancreatic trypsin inhibitor (BPTI) crystallized from a thiocyanate solution has been determined and refined at 2.7 A resolution. The space group is P21 with a = 71.56, b = 73.83, c = 64.47 A, beta = 93.9 degrees and Z = 20. The ten independent molecules were located by a multi-body molecular-replacement search as developed in the AMoRe program, starting from a single monomer model (PDB code: 6PTI). The molecular arrangement of the subunits is a decamer resulting from the combination of two orthogonal fivefold and twofold non-crystallographic axes. This builds a globular micelle-like particle which minimizes hydrophobic interactions with the solvent. The refinement was conducted with non-crystallographic symmetry constraints up to a final residual of R = 0.20 (Rfree= 0.26). The root-mean-square deviations from ideal geometry were 0.015 A and 1.6 degrees on bond distances and bond angles, respectively. Several sites for thiocyanate ions were analyzed.

Animals↗
PubMed1993

Inhibitory effects of benzyl isothiocyanate and benzyl thiocyanate on diethylnitrosamine-induced hepatocarcinogenesis in rats.

The effects of two aromatic thiocyanates, benzyl isothiocyanate (BITC) and benzyl thiocyanate (BTC), on diethylnitrosamine (DEN)-induced hepatocarcinogenesis were examined in rats. A total of 108 male ACI/N rats, 5 weeks old, were divided into 6 groups (18 rats in each). Group 1 was given a single i.p. injection of DEN (200 mg/kg body weight) one week after the start of the experiment and then kept on the basal diet until the end of the experiment (1 year). Groups 2 and 3 were treated with DEN and received dietary BITC (100 ppm) or BTC (100 ppm), respectively, throughout the experimental duration. Groups 4 and 5 were not given the carcinogen and were fed the diet containing BITC or BTC, respectively. Group 6 was kept on the basal diet alone and served as a control. Liver neoplasms were seen in Groups 1, 2 and 3. Incidence and average number of liver neoplasms in Group 2 were significantly smaller than in Group 1 (P < 0.0005 and P < 0.001, respectively). The incidence of liver neoplasms in Group 3 was slightly lower than in Group 1, although the difference was not statistically significant. The numbers of glutathione S-transferase placental form (GST-P)-positive foci in Group 2 and gamma-glutamyltranspeptidase (GGT)-positive foci in Groups 2 and 3 were significantly smaller than those in Group 1 (P < 0.001). The average and unit areas of GST-P- or GGT-positive foci in Group 2 or 3 were also significantly smaller than those in Group 1 (P < 0.05). These results suggest that BITC and BTC are chemopreventive agents for DEN-induced liver tumorigenesis.

Animals↗