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PubMed1988

Asymmetric incorporation of [14C]cyanate and of fluorescein isothiocyanate in mamillary body of conditioned rats.

A marked decrease in overall learning capacity has been observed in rats injected with cyanate. Therefore it was of interest to test whether learning influenced carbamylation of brain proteins. Incorporation of [14C]cyanate into proteins of the mamillary body was selectively modified following operant conditioning of the rat, so that trained rats showed an asymmetric image with higher levels of incorporation in the right side than in the left side, as compared to control rats. These results were confirmed using fluorescein isothiocyanate. The asymmetry persisted once the learning had been well established.

Animals↗
PubMed1996

Cell-free extract(s) of Pseudomonas putida catalyzes the conversion of cyanides, cyanates, thiocyanates, formamide, and cyanide-containing mine waters into ammonia.

Our isolate, Pseudomonas putida, is known to be capable of utilizing cyanides as the sole source of carbon (C) and nitrogen (N) both in the form of free cells and cells immobilized in calcium alginate. In the present study, the cell-free extract(s) were prepared from the cells of P. putida grown in the presence of sodium cyanide. The ability of enzyme(s) to convert cyanides, cyanates, thiocyanates, formamide and cyanide-containing mine waters into ammonia (NH3) was studied at pH 7.5 and pH 9.5. The kinetic analysis of cyanide and formamide conversion into NH3 at pH 7.5 and pH 9.5 by the cell-free extract(s) of P. putida was also studied. The Km and Vmax values for cyanide/formamide were found to be 4.3/8 mM and 142/227 mumol NH3 released mg protein-1 min-1 respectively at pH 7.5 and 5/16.67 mM and 181/434 mumol NH3 released mg protein-1 h-1 respectively at pH 9.5. The study thus concludes that the cell-free extract(s) of P. putida is able to metabolize not only cyanides, cyanates, thiocyanates, and formamide but also cyanide-containing mine waters to NH3.

Ammonia↗
PubMed1986

Tropomyosin's end-to-end polymerization is irreversibly lost on exposure to urea or cyanate.

Tropomyosin's low-salt viscosity which is due to end-to-end polymerization, is irreversibly lost upon incubation in 8M urea at room temperature. This effect is due to the chemical modification of lysine residues by cyanate in the urea. In the absence of urea, cyanate alone has the same effect. A loss in tropomyosin binding to actin accompanies the loss in viscosity, consistent with the view that tropomyosin's end-to-end interaction is necessary for strong binding to actin. During column chromatography in 8M urea, used to separate the alpha and beta chains of tropomyosin, the loss of viscosity can be minimized by using freshly-prepared urea and by reducing the time during which the protein and urea are in contact.

Actins↗
PubMed1998

Quantification of carbamylated dehydroascorbate derivative produced from cyanate and dehydroascorbate.

We established a high-performance liquid chromatographic method for separating and quantifying carbamylated dehydroascorbate derivative (CDA), a reaction product of cyanate with dehydroascorbate. The separation of CDA from interfering substances was achieved by anion-exchange HPLC using a TSK gel SAX (250x4.6 mm I.D.) column and 0.12 M NaCl eluent. The detection of CDA was achieved through two steps: (1) degradation of CDA to cyanate and amino compounds in alkaline solution, and (2) detection of these products by an indophenol reaction. For the processing of plasma and urine samples, anion-exchange solid-phase extraction was used. The detection limit for quantitative determination was 0.1 microM CDA (S/N=3). The linear range found applying the optimized conditions was 0.2 to 200 microM. The intra- and inter-day assay precision (R.S.D.) of CDA (10 microM) were 4.8 and 7.2% for rat plasma, and 4.0 and 4.9% for rat urine, respectively. The usefulness of the present method was proved by the application to plasma and urine samples. The study of the biokinetics of CDA in rats revealed that the elimination of CDA is due to urinary excretion.

Animals↗
PubMed1997

Inactivation of glyceraldehyde 3-phosphate dehydrogenase by sugars, prednisolone-21-hemisuccinate, cyanate and other small molecules.

Diabetes, diarrhoea, renal failure and glucocorticoid therapy have all been identified as independent risk factors for cataract. Increased post-translational modification of proteins, leading to inactivation of enzymes and induction of conformational changes within proteins could result in lens opacification and cataract. Aspirin has been associated with many beneficial effects, including protection against cataract, in-vivo. alpha-Crystallin has been shown to act as a molecular chaperone in-vitro. This lenticular protein prevented the thermal aggregation of other lens proteins in-vitro and has sequence and functional homology with the small heat shock proteins. Glyceraldehyde 3-phosphate dehydrogenase (GAP-DH) is constitutively expressed in tissues and is susceptible to chemical modification in-vivo. In-vitro incubations of GAP-DH with sugars, cyanate and prednisolone-21-hemisuccinate, all led to significant loss of enzyme activity with time in two buffer systems. Rapid inactivation occurred when GAP-DH was incubated with fructose 6-phosphate or prednisolone-21-hemisuccinate. Slower inactivation was observed when GAP-DH was incubated with fructose, glucose 6-phosphate or potassium cyanate. Glucose did not inactivate GAP-DH under the conditions of our experiments. Aspirin and ibuprofen were shown to inactivate GAP-DH very rapidly in-vitro. Bovine lenticular alpha-crystallin conferred no protection against GAP-DH inactivation. This is the first occasion that alpha-crystallin has been demonstrated to be unable to protect against inactivation in our chemical enzyme inactivation system. This may have implications for the susceptibility of lenticular GAP-DH to post-translational inactivation.

Animals↗
PubMed2006

The peptide formation mediated by cyanate revisited. N-carboxyanhydrides as accessible intermediates in the decomposition of N-carbamoylamino acids.

Similar to many ureas, N-carbamoylamino acids were shown to be hydrolyzed in aqueous solution through elimination mechanisms at close to neutral pH, the nucleophilic attack of water being a minor process. Two competing elimination mechanisms can take place involving either cyanate or isocyanate transient intermediates. Peptide formation was observed and attributed to the latter pathway through the intermediacy of amino acid N-carboxyanhydride (NCA). Eventually, cyanate and its precursors (including urea) unexpectedly behave as amino acid activating agents because of their ability in amino acid carbamoylation. Owing to its ability to generate a background prebiotic production of NCAs on the primitive Earth, this reaction is suggested to have contributed to the origin of life process.

Amino Acids↗
PubMed2006

Highly enantioselective cyanation of aldehydes catalyzed by a multicomponent titanium complex.

A new multicomponent bifunctional catalytic system based on a titanium complex was used for the efficient enantioselective cyanation of aldehydes. The catalyst was readily prepared from tetraisopropyl titanate (Ti(Oi-Pr)4), (S)-6,6'-dibromo-1,1'-bi-2-naphthol (1e), cinchonine (2a), and (1R,2S)-(-)-N-methylephedrine (3b). It was revealed that the combination of 1e, 2a, 3b, and Ti(IV) was essential in this cyanation. The reaction proceeded smoothly in the presence of a catalytic amount of the multicomponent catalyst to afford the desired cyanohydrins ethyl carbonates in moderate to excellent isolated yields (up to 95%) with high enantioselectivities (up to 94% ee). A catalytic cycle based on experimental phenomena was proposed to explain the origin of the asymmetric induction.

Aldehydes↗
PubMed1989

Site of carbamoylation of bovine gamma-II-crystallin by potassium [14C]cyanate.

One possible route to cataract formation may be via the carbamoylation of lens proteins due to increased concentrations of cyanate in the body resulting from uraemia associated with renal failure and with severe diarrhoea. Carbamoylation of gamma-II-crystallin, which is found in the lens core, could alter the surface charge network of the molecules, resulting in aggregation, increased light-scattering and hence cataract. We have attempted to locate the site(s) of carbamoylation in gamma-II-crystallin. gamma-II-Crystallin was isolated by gel chromatography and ion-exchange chromatography. gamma-II-Crystallin was then carbamoylated by incubation with potassium [14C]cyanate, followed by citraconylation and digestion with trypsin to give peptides that were separated by high-resolution ion-exchange chromatography. The amino acid compositions of the radioactive peptides were compared with the expected peptide composition for gamma-II-crystallin. The radioactive peptide compositions, which agreed with the theoretical peptides, all matched with the N-terminal region of gamma-II-crystallin and had in common the presence of the N-terminal glycine residue. It appears that the alpha-amino group of the N-terminal glycine was the main site of carbamoylation. This site forms part of the charge network on the surface of gamma-II-crystallin.

Amino Acids↗
PubMed1987

Measurement of phagocytosis utilizing [14C]cyanate-labelled human red cells and monocytes.

Human red cells were labelled with [14C]cyanate, non-oxidant, permeant reagent that binds irreversibly to amino groups in proteins. Cyanate did not modify GSH levels, nor glucose-6-phosphate dehydrogenase (G6PD) activity when added at the labelling concentration i.e. c. 0.5 mM. Phagocytes were human monocytes, isolated and plated on 16 mm diameter plastic wells. Each well was plated with 40-70 X 10(3) cells. Monocytes were quantified by DNA assay with the DNA intercalating fluorescent compound Hoechst 33,258. The basal phagocytic rate of normal red cells by monocytes was 0.34 +/- 0.21 red cell per monocyte. Treatment of normal red cells with 20 microM diamide, or 50-100 microM chromate enhanced this rate 10-15-fold. 10 microM diamide or chromate were sufficient to stimulate phagocytosis of G6PD-deficient (Mediterranean variant) red cells.

Carbon Radioisotopes↗
PubMed1985

Phase-I clinical trial of sodium cyanate in patients with advanced colorectal carcinoma.

Sodium cyanate, a drug that selectively suppresses amino acid incorporation for protein synthesis in tumor tissue, was given to patients with advanced colorectal carcinoma who had failed to conventional therapy, with the purpose of assessing a maximum tolerable oral dose. At 35 mg/kg p.o. daily, the drug had to be stopped in approximately half (4) of the patients because of gastrointestinal toxicity (nausea, vomiting) and neurologic toxicity (hallucinations, disorientation). However, in 5 other patients, at the same dose, the drug was well tolerated for up to 147 days and for a total cumulative dose of 308 g. In this group of patients, sodium cyanate was stopped because of evidence of tumor progression. No hematologic toxicity was observed. We observed no therapeutic effects. We therefore recommend a starting dose of 30 mg/kg p.o. if a phase-II study is considered.

Adult↗
PubMed2005

Allyl cyanate-to-isocyanate rearrangement for the synthesis of quaternary stereocenter with nitrogen substituent.

The stereochemistry and efficiency of an allyl cyanate-to-isocyanate rearrangement for the construction of quaternary stereocenter with nitrogen substituent was investigated by the synthesis of (R)-alpha-methylphenylalanine. The rearrangement was found to be stereospecific, and the chirality of allyl carbamate was transferred to that of the quaternary carbon bearing isocyanate group. These results establish that an allyl cyanate-to-isocyanate rearrangement is a useful method for the synthesis of natural products, that contain the quaternary carbon with nitrogen substituent.

Allyl Compounds↗
PubMed1976

Reactivity of cyanate with valine-1 (alpha) of hemoglobin. A probe of conformational change and anion binding.

The 3-fold increase in the carbamylation rate of Val-1 (alpha) of hemoglobin upon deoxygenation described earlier is now shown to be a sensitive probe of conformational change. Thus, whereas this residue in methemoglobin A is carbamylated at the same rate as in liganded hemoglobin, upon addition of inositol hexaphosphate its carbamylation rate is enhanced 30% as much as the total change in the rate between the CO and deoxy states. For CO-hemoglobin Kansas in the presence of the organic phosphate, the relative increase in the carbamylation rate of this residue is about 50%. These results indicate that methemoglobin A and hemoglobin Kansas in the presence of inositol hexaphosphate do not assume a conformation identical with deoxyhemoglobin but rather form either a mixture of R and T states or an intermediate conformation in the region around Val-1 (alpha). Studies on the mechanism for the rate enhancement in deoxyhemoglobin suggest that the cyanate anion binds to groups in the vicinity of Val-1 (alpha) prior to proton transfer and carbamylation of this NH2-terminal residue. Thus, specific removal with carboxypeptidase B of Arg-141 (alpha), which is close to Val-1 (alpha) in deoxyhemoglobin, abolishes the enhancement in carbamylation. Chloride, which has the same valency as cyanate, is a better competitive inhibitor of the carbamylation of deoxyhemoglobin (Ki = 50 mM) compared with liganded hemoglobin. Nitrate and iodide are also effective inhibitors of the carbamylation of Val-1 (alpha) of deoxyhemoglobin (Ki = 35 mM); inorganic phosphate, sulfate, and fluoride are poor competitive inhibitors. The change in pKa of Val-1 (alpha) upon deoxygenation may be due to its differential interaction with chloride.

Anions↗
PubMed1975

Enhancement of filterability of sickle cells by cyanate: an effect independent of oxygen saturation.

Filterability and morphology of cyanate-treated sickle cells were compared to those of untreated cells at equal oxygen saturations to determine whether carbamylation inhibited sickling by an effect other than by its alteration of the oxygen dissociation curve. Morphology of treated and untreated cells was not significantly different at all levels of oxygen saturation examined. Filterability, on the other hand, was improved significantly by carbamylation. This latter finding indicates that carbamylation enhances deformability of sickle cells by a mechanism(s) in addition to its effect on red cell oxygen saturation. This mechanism(s) may account for the clinical benefit of cyanate therapy with doses which do not significantly affect the oxygen dissociation curve.

Adenosine Triphosphate↗
PubMed1975

Toxic-therapeutic ratio of sodium cyanate.

Six patients with sickle cell anemia were treated with sodium cyanate (30 mg/kg/day). In four, treatment was stopped because of definite or suspected toxicity, and no improvement was seen in the other two. Most alarming was the sudden development of peripheral motor neuropathy in a patient whose red blood cells contained less than 0.6 mols NCO-/mol of hemoglobin: six months after treatment was stopped, function had not completely returned in this patient. Safe oral dosage regimens may not be effective, but extra-corporeal treatment of sickle cells with cyanate, or other compounds, might circumvent that problem.

Adult↗
PubMed1975

Iron metabolism, sickle cell disease, and response to cyanate.

In an attempt to understand the variability of the hematologic response to oral sodium cyanate, iron metabolism was studied in a group of 39 patients with sickel cell disease. Eleven of the 39 patients were found to have no stainable iron in the marrow despite the fact that patients with sickle cell disease are generally considered to have hemosiderosis. The mean per cent saturation and total iron-binding capacity were in the low-normal range in sickle cell patients whether or not stainable iron was present in the bone marrow aspirate. Serum ferritin concentrations, on the other hand, were found to be high in both groups (greater than 500 mu g/liter) when compared to controls (60 mu g/liter). The high serum ferritin levels denoted significant total-body iron deposition which may be unavailable for normal metabolic processes. One patient with no stainable iron in the bone marrow aspirate did respond to iron therapy alone with an increase in hemoglobin concentration. Serum ceruloplasmin levels were also found to be high in sickle cell disease patients. The ability to respond to oral cyanate therapy was correlated with the amount of stainable iron in the bone marrow aspirate. These studies emphasize the necessity of a reevaluation of iron metabolism in the pathophysiology and treatment of sickle cell disease.

Administration, Oral↗
PubMed1976

Extracorporeal treatment with cyanate in sickle cell disease: preliminary observations in four patients.

The effects of extracorporeal carbamylation were determined in four patients with sickle cell anemia. Treatments were carried out in clusters every 4 to 6 weeks over a 6-month period. Mean carbamylation achieved in vivo was 1.3 moles cyanate per mole of hemoglobin. The mean in vitro P50 during treatment was 22.1 mm. Hg as compared to the pretreatment value of 30 mm. Hg. Hemoglobin concentration was increased over the 6 months by 24 per cent. The treatment resulted in the stimulation of erythropoiesis. Treated cells had a prolonged survival of about 40 days, but bilirubin did not fall. Blood volume and heart size remained unchanged. Carbamylation did not appear to alter the degree of sickling at any given O2 saturation. Painful attacks continued through the treatment period with a frequency of 84 per cent and a severity-frequency index of 77 per cent of that in the control period. There was no evidence of cyanate toxicity associated with extracorporeal therapy.

Adult↗
PubMed1992

[The effect of sodium cyanate-modified hemoglobin oxygen affinity on the heat resistance of rats].

Regression analysis of relationship between rat hemoglobin-oxygen affinity (HOA) and rectal temperature has shown a close positive correlation of these parameters. Heat resistance (HR) was examined in rats with HOA elevated by sodium cyanate in order to recognize the contribution of HOA to a process of body heat adaptation. Our data suggest that HR of treated rats was larger than in control animals. These results are discussed in relation with antioxidant type of the cyanate elevation in HOA.

Adaptation, Physiological↗