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PubMed1976

Inactivation of bovine liver 2-keto-4-hydroxyglutarate aldolase by cyanide in the presence of aldehydes.

Kinetic data show that the irreversible inactivation of liver 2-keto-4-hydroxyglutarate aldolase observed when the enzyme is incubated with an aldehydic substrate (or substrate analogue) in the presence of cyanide is a biphasic process and can, under certain conditions, involve a direct interaction between the enzyme and cyanide. The kinetic data are consistent with a scheme consisting of three competing reactions: (1) irreversible addition of cyanide to the enzyme-substrate Schiff base intermediate, (2) reversible cyanohydrin formation between cyanide and the aldehydic substrate (or substrate analogue), and (3) an interaction of cyanide with the enzyme which is not substrate dependent. Approximately 0.4 mol of cyanide is associated with 1 mol (120 000 g) of enzyme when 2-keto-4-hydroxyglutarate aldolase is incubated with [14-C]-cyanide followed by exhaustive dialysis; an ionic attachment possibly at a carboxylate binding site, is suggested. Whereas native enzyme, not treated with cyanide, has ten Nbs2-titratable sulfhydryl groups, approximately one less such group reacts with Nbs2 when the aldolase is incubated with cyanide (in the absence of aldehydic substrate). It is suggested that the binding of cyanide results in a conformational change of the enzyme; conformational changes in the presence of cyanide are confirmed by circular dichroism spectra.

Animals↗
PubMed2001

Interaction of acetylene and cyanide with the resting state of nitrogenase alpha-96-substituted MoFe proteins.

The nitrogenase MoFe protein contains the active site metallocluster called FeMo-cofactor [7Fe-9S-Mo-homocitrate] that exhibits an S = 3/2 EPR signal in the resting state. No interaction with FeMo-cofactor is detected when either substrates or inhibitors are incubated with MoFe protein in the resting state. Rather, the detection of such interactions requires the incubation of the MoFe protein together with its obligate electron donor, called the Fe protein, and MgATP under turnover conditions. This indicates that a more reduced state of the MoFe protein is required to accommodate substrate or inhibitor interaction. In the present work, substitution of an arginine residue (alpha-96(Arg)) located next to the active site FeMo-cofactor in the MoFe protein by leucine, glutamine, alanine, or histidine is found to result in MoFe proteins that can interact with acetylene or cyanide in the as-isolated, resting state without the need for the Fe protein, or MgATP. The dithionite-reduced, resting states of the alpha-96(Leu)-, alpha-96(Gln)-, alpha-96(Ala)-, or alpha-96(His)-substituted MoFe proteins show an S = 3/2 EPR signal (g = 4.26, 3.67, 2.00) similar to that assigned to FeMo-cofactor in the wild-type MoFe protein. However, in contrast to the wild-type MoFe protein, the alpha-96-substituted MoFe proteins all exhibit changes in their EPR spectra upon incubation with acetylene or cyanide. The alpha-96(Leu)-substituted MoFe protein was representative of the other alpha-96-substituted MoFe proteins examined. The incubation of acetylene with the alpha-96(Leu) MoFe protein decreased the intensity of the normal FeMo-cofactor signal with the appearance of a new EPR signal having inflections at g = 4.50 and 3.50. Incubation of cyanide with the alpha-96(Leu) MoFe protein also decreased the FeMo-cofactor EPR signal with concomitant appearance of a new EPR signal having an inflection at g = 4.06. The acetylene- and cyanide-dependent EPR signals observed for the alpha-96(Leu)-substituted MoFe protein were found to follow Curie law 1/T dependence, consistent with a ground-state transition as observed for FeMo-cofactor. The microwave power dependence of the EPR signal intensity is shifted to higher power for the acetylene- and cyanide-dependent signals, consistent with a change in the relaxation properties of the spin system of FeMo-cofactor. Finally, the alpha-96(Leu)-substituted MoFe protein incubated with (13)C-labeled cyanide displays a (13)C ENDOR signal with an isotropic hyperfine coupling of 0.42 MHz in Q-band Mims pulsed ENDOR spectra. This indicates the existence of some spin density on the cyanide, and thus suggests that the new component of the cyanide-dependent EPR signals arise from the direct bonding of cyanide to the FeMo-cofactor. These data indicate that both acetylene and cyanide are able to interact with FeMo-cofactor contained within the alpha-96-substituted MoFe proteins in the resting state. These results support a model where effective interaction of substrates or inhibitors with FeMo-cofactor occurs as a consequence of both increased reactivity and accessibility of FeMo-cofactor under turnover conditions. We suggest that, for the wild-type MoFe protein, the alpha-96(Arg) side chain acts as a gatekeeper, moving during turnover in order to permit accessibility of acetylene or cyanide to a specific [4Fe-4S] face of FeMo-cofactor.

Acetylene↗
PubMed2005

Enhanced fluorescence cyanide detection at physiologically lethal levels: reduced ICT-based signal transduction.

Three water-soluble fluorescent probes have been specifically designed to determine free cyanide concentrations up to physiologically lethal levels, >20 microM. The probes have been designed in such a way as to afford many notable sensing features, which render them unique with regard to signal transduction, photophysical characteristics, and their application to physiological cyanide determination and safeguard. The probes are readily able to reversibly bind free aqueous cyanide with dissociation constants around 4 microM3. Subsequent cyanide binding modulates the intramolecular charge transfer within the probes, a change in the electronic properties within the probes, resulting in enhanced fluorescence optical signals as a function of increased solution cyanide concentration. The ground-state chelation with cyanide produces wavelength shifts, which also enable the probes to sense cyanide in both an excitation and emission ratiometric manner, in addition to enhanced fluorescence signaling. This has enabled a generic cyanide sensing platform to be realized that is not dependent on fluorescent probe concentration, probe photodegradation, or fluctuations in the intensity of any employed excitation sources, ideal for remote cyanide sensing applications. Further, the >600 nm fluorescence emission of the probes potentially allows for enhanced fluorescence ratiometric cyanide sensing in the optical window of tissues and blood, facilitating their use for the transdermal monitoring of cyanide for mammalian safeguard or postmortem in fire victims, both areas of active research.

Cyanides↗
PubMed2004

Toxicity and degradation of metal-complexed cyanide by a bacterial consortium under sulfate-reducing conditions.

Free cyanide at 1 mm decreased the initial sulfate reduction rate of a batch culture of granular sludge from 0.3 to 0.14 mmol d(-1) g(-1) SS (suspended solid), whereas 0.5 mm cyanide had a minimal effect (0.25 mmol d(-1) g(-1) SS). The order of toxicity of metal-complexed cyanides to the sludge was as follows: zinc-complexed cyanide (most toxic) > free cyanide = nickel-complexed cyanide > copper-complexed cyanide (least toxic), which also corresponds well with the order of the stability (dissociation) constants of the metal-cyanide complexes. A consortium degrading cyanide was enriched using nickel cyanide as the sole nitrogen source. This consortium completely removed 0.5 mm of nickel-complexed cyanide under sulfate-reducing conditions in 11 d. Analysis of clone library of 16S rRNA genes shows that the consortium was composed of three major phylotypes including Desulfovibrio.

Bacteria, Anaerobic↗
PubMed1991

Elevated blood cyanide concentrations in victims of smoke inhalation.

BACKGROUND: The nature of the toxic gases that cause death from smoke inhalation is not known. In addition to carbon monoxide, hydrogen cyanide may be responsible, but its role is uncertain, because blood cyanide concentrations are often measured only long after exposure. METHODS: We measured cyanide concentrations in blood samples obtained at the scene of residential fires from 109 fire victims before they received any treatment. We compared the results with those in 114 persons with drug intoxication (40 subjects), carbon monoxide intoxication (29 subjects), or trauma (45 subjects). The metabolic effect of smoke inhalation was assessed by measuring plasma lactate at the time of admission to the hospital in 39 patients who did not have severe burns. RESULTS: The mean (+/-SD) blood cyanide concentrations in the 66 surviving fire victims (21.6 +/- 36.4 mumol per liter, P less than 0.001) and the 43 victims who died (116.4 +/- 89.6 mumol per liter, P less than 0.001) were significantly higher than those in the 114 control subjects (5.0 +/- 5.5 mumol per liter). Among the 43 victims who died, the blood cyanide concentrations were above 40 mumol per liter in 32 (74 percent), and above 100 mumol per liter in 20 of these (46 percent). There was a significant correlation between blood cyanide and carbon monoxide concentrations in the fire victims (P less than 0.001). Plasma lactate concentrations at the time of hospital admission correlated more closely with blood cyanide concentrations than with blood carbon monoxide concentrations. Plasma lactate concentrations above 10 mmol per liter were a sensitive indicator of cyanide intoxication, as defined by the presence of a blood cyanide concentration above 40 mumol per liter. CONCLUSIONS: Residential fires may cause cyanide poisoning. At the time of a patient's hospital admission, an elevated plasma lactate concentration is a useful indicator of cyanide toxicity in fire victims who do not have severe burns.

Adolescent↗
PubMed2005

Cyanide removal by Chinese vegetation--quantification of the Michaelis-Menten kinetics.

BACKGROUND: Little is known about metabolism rates of environmental chemicals by vegetation. A good model compound to study the variation of rates among plant species is cyanide. Vascular plants possess an enzyme system that detoxifies cyanide by converting it to the amino acid asparagine. Knowledge of the kinetic parameters, the half-saturation constant (Km) and the maximum metabolic capacity (vmax), is very useful for enzyme characterization and biochemical purposes. The goal of this study is to find the enzyme kinetics (K(M) and vmax) during cyanide metabolism in the presence of Chinese vegetation, to provide quantitative data for engineered phytoremediation, and to investigate the variation of metabolic rates of plants. METHODS: Detached leaves (1.0 g fresh weight) from 12 species out of 9 families were kept in glass vessels with 100 mL of aqueous solution spiked with potassium cyanide at 23 degrees C for 28 h. Four different treatment concentrations of cyanide were used, ranging from 0.44 to 7.69 mg CN/L. The disappearance of cyanide from the aqueous solution was analyzed spectrophotometrically. Realistic values of the half-saturation constant (KM) and the maximum metabolic capacity (vmax) were estimated by a computer program using non-linear regression treatments. As a comparison, Lineweaver-Burk plots were also used to estimate the kinetic parameters. RESULTS AND DISCUSSION: The values obtained for K(M) and vmax varied with plant species. Using non-linear regression treatments, values of vmax and K(M) were found in a range between 6.68 and 21.91 mg CN/kg/h and 0.90 to 3.15 mg CN/L, respectively. The highest vmax was by Chinese elder (Sambucus chinensis), followed by upright hedge-parsley (Torilis japonica). The lowest Vmax was demonstrated by the hybrid willow (Salix matssudana x alba). However, the highest K(M) was found in the water lily (Nymphea teragona), followed by the poplar (Populus deltoides Marsh). The lowest K(M) was demonstrated by corn (Zea mays L.). The values of vmax were normally distributed with a mean of 13 mg CN/kg/h. CONCLUSIONS: Significant removal of cyanide from aqueous solution was observed in the presence of plant materials without phytotoxicity, even at high doses of cyanide. This gives rise to the conclusion that the Chinese plant species used in this study are all able to efficiently metabolize cyanide, although with different maximum metabolic capacities. A second conclusion is that the variation of metabolism rates between species is small. All these plants had a similar K(M), indicating the same enzyme is active in all plants. RECOMMENDATIONS AND OUTLOOK: Detoxification of cyanide with trees seems to be a feasible option for cleaning soils and water contaminated with cyanide. For phytoremediation projects, screening appropriate plant species adapted to local conditions should be seriously considered. More chemicals should be investigated to find common principles of the metabolism of environmental chemicals by plants.

Biodegradation, Environmental↗
PubMed2002

Morphological transformation and oxidative stress induced by cyanide in Syrian hamster embryo (SHE) cells.

Cyanide is a well-established poison known for its rapid lethal action and toxicity. Although long-term mammalian studies examining the carcinogenic potential of cyanide have not been previously reported, cyanide was reported to be positive in Salmonella typhimurium mutagenesis assay and induced aneuploidy in Drosophila. To further evaluate the carcinogenic potential of cyanide, the ability of cyanide to induce morphological transformation in Syrian hamster embryo (SHE) cells was studied. Cyanide induced a dose-dependent increase in morphological transformation in SHE cells following a 7-day continuous treatment. A significant increase in transformation was observed at potassium cyanide doses of 200 microM and greater. Transformation induced by cyanide was inhibited in a dose-related manner by vitamin E, suggesting a role of oxidative stress in the induction of morphological transformation by cyanide. Further, it was shown that 500 microM cyanide induced oxidative DNA damage in SHE cells, evidenced by the formation of 8-hydroxy-2'-deoxyguanosine (50-66% increase over control). The induction of oxidative stress by cyanide involved an early and temporal inhibition of antioxidant enzymes (catalase and superoxide dismutase) as well as an increased production of reactive oxygen species (1.5- to 2.0-fold over control).

8-Hydroxy-2'-Deoxyguanosine↗
PubMedDate not supplied

Identification of a crystalline cyanide-containing compound in blast furnace sludge deposits.

During blast furnace operation, a cyanide-containing muddy waste referred to as blast furnace sludge is generated in large amounts. In Germany it was and is still common practice to pump this sludge into surface deposits. Depending on species, cyanide has very different toxicity. To this day there is no information about the type of cyanide occurring in blast furnace sludge deposits. In order to identify the type of cyanide we investigated by means of wet chemical and powder X-ray diffraction analyses 37 samples of three blast furnace deposits. Wet chemical results indicate that both the extremely toxic free cyanide (HCN and CN ) and toxic weak metal-cyanide complexes, for example [Zn(CN)4]2-, are not present in the sludge. By powder X-ray diffraction we identified the crystalline cyanide-containing compound potassium zinc hexacyanoferrate(II) nonahydrate, K2Zn3[Fe(CN)6]2 x 9H2O, as the cyanide-bearing compound. Our study is the first that identifies potassium zinc hexacyanoferrate(II) nonahydrate in the environment. As the iron-cyanide complex [Fe(CN)6] is not acutely toxic, any direct hazard comes from cyanide occurring in the investigated wastes. Under the predominant pH milieu of the sludge (pH about 8) the solubility of potassium zinc hexacyanoferrate(II) nonahydrate is low, thus minimizing the mobility of cyanide.

Environmental Monitoring↗
PubMed1986

Clinical features and management of cyanide poisoning.

The pathophysiology, clinical features, and management of cyanide toxicity are reviewed and sources of cyanide are listed. Cyanide is a deadly poison that is found in many foods and household and industrial products, including some that are readily available. Cyanide binds with cytochrome oxidase, the enzyme responsible for oxidative phosphorylation, and paralyzes cellular respiration. Because the tissues cannot use oxygen that is delivered, aerobic metabolism ceases. The signs and symptoms of cyanide poisoning reflect the extent of cellular hypoxia. Manifestations may include respiratory abnormalities (progressing from tachypnea and dyspnea to respiratory depression and apnea), hemodynamic instability, metabolic acidosis, and, possibly, local irritant effects after oral ingestion of cyanide. The mainstays of therapy are 100% oxygen and specific antidotes to cyanide. Sequential treatment with amyl nitrite by inhalation, intravenous sodium nitrite 3%, and intravenous sodium thiosulfate 25% is directed toward decreasing the amount of cyanide available for cellular binding. Nitrites convert hemoglobin to methemoglobin, which reacts with cyanide to form cyanomethemoglobin. Sodium thiosulfate serves as a source of sulfur groups, which are needed for conversion of cyanide to thiocyanate, a compound that is relatively less toxic and is excreted renally. Supportive care also is important. Cobalt EDTA, hydroxocobalamin, and aminophenols have also been used but are not considered standard treatments. Cyanide poisoning is a medical emergency that requires prompt recognition and immediate and aggressive treatment.

Antidotes↗
PubMed2000

Factors affecting the biodegradation of cyanide by Burkholderia cepacia strain C-3.

The utilization of cyanide as a nitrogen source for growth in a liquid minimal medium by Burkholderia cepacia strain C-3 isolated from soil was demonstrated. The effects of various parameters on the biodegradation of cyanide by the strain were investigated. Growth at the expense of cyanide occurred over a pH range from 8 to 10, and was optimal at pH 10. Growth and cyanide biodegradation were optimal at 30 degrees C. The presence of Cu2+ or Fe2+ in the liquid medium at a concentration of 1 mM inhibited both the growth of the bacterium and its cyanide degradation. The effects of Ni2+ and Co2+, and to a lesser extent Mn2+ and Mo2+, on cyanide degradation rate were concentration dependent. Addition of the cyanide-containing waste contaminants ethanol and methanol reduced the cyanide utilization of the isolate, but phenol was completely inhibitory. Microbial depletion of cyanide occurred even in the presence of other organic and inorganic nitrogen sources. Fructose, glucose, and mannose were the preferred carbon sources for cyanide biodegradation. The highest rate of cyanide degradation by B. cepacia C-3, 1.85 mg CN h(-1), was observed with 0.25% (w/v) fructose; the degradation rate decreased progressively thereafter with increasing fructose concentration.

Journal Article↗
PubMed2006

Uptake of iron cyanide complexes into willow trees.

The uptake of iron cyanide into willows was studied. Trees were grown in solutions with Prussian blue, ferricyanide, or ferrocyanide. Iron cyanide speciation in solution was determined by HPLC during the experiment. Total cyanide and total iron in solution and trees were measured at the end of the experiments. Ferrocyanide wasthe dominating species in most solutions at the end. Ferricyanide was preferably taken up from solutions. Between 20 and 83% of the cyanide was lost from the solutions, and up to 28% could be recovered from the plants, mainly from roots. Cyanide could also be detected in stems and leaves of most exposed trees. Uptake was increased when no other nitrogen source but cyanide was present in solutions. Iron contents in exposed trees, compared to controls, increased significantly. The ratio of iron to cyanide remained rather stable in solution, but changed to higher values inside the plants. This indicates that iron and cyanide were taken up together as a complex, which was dissolved inside plants, and then cyanide was metabolized. No toxic effects could be seen. The study shows that trees can take up and metabolize iron cyanide complexes, making phytoremediation of iron cyanide waste a feasible option.

Chromatography, High Pressure Liquid↗
PubMed1997

Cyanide Degradation under Alkaline Conditions by a Strain of Fusarium solani Isolated from Contaminated Soils.

Several cyanide-tolerant microorganisms have been selected from alkaline wastes and soils contaminated with cyanide. Among them, a fungus identified as Fusarium solani IHEM 8026 shows a good potential for cyanide biodegradation under alkaline conditions (pH 9.2 to 10.7). Results of K(sup14)CN biodegradation studies show that fungal metabolism seems to proceed by a two-step hydrolytic mechanism: (i) the first reaction involves the conversion of cyanide to formamide by a cyanide-hydrolyzing enzyme, cyanide hydratase (EC 4.2.1.66); and (ii) the second reaction consists of the conversion of formamide to formate, which is associated with fungal growth. No growth occurred during the first step of cyanide degradation, suggesting that cyanide is toxic to some degree even in cyanide-degrading microorganisms, such as F. solani. The presence of organic nutrients in the medium has a major influence on the occurrence of the second step. Addition of small amounts of yeast extract led to fungal growth, whereas no growth was observed in media containing cyanide as the sole source of carbon and nitrogen. The simple hydrolytic detoxification pathway identified in the present study could be used for the treatment of many industrial alkaline effluents and wastes containing free cyanide without a prior acidification step, thus limiting the risk of cyanhydric acid volatilization; this should be of great interest from an environmental and health point of view.

Journal Article↗
PubMed1984

Alternate substrates of dopamine beta-hydroxylase. III. Stoichiometry of the inactivation reaction with benzyl cyanides and spectroscopic investigations.

Dopamine beta-hydroxylase was incubated with p-hydroxybenzyl cyanide, ascorbate, and O2 and the products of the hydroxylation reaction were monitored by high performance liquid chromatography. At early times, p-hydroxymandelonitrile was the sole product but this compound slowly decomposed to p-hydroxybenzaldehyde and cyanide. Dopamine beta-hydroxylase was also inhibited under these reaction conditions but the amount of cyanide produced was insufficient to account for the extent of enzyme inhibition. Incubation of dopamine beta-hydroxylase with [ring-3H]p-hydroxybenzyl cyanide, ascorbate, and O2 resulted in incorporation of detectable radiolabel into enzyme only when 100% O2 (0.4 X Km) was present. The amount of incorporated radiolabel was substoichiometric with respect to enzyme subunits (approximately 30%) and also did not correlate with the total amount of inhibited dopamine beta-hydroxylase. These data suggest two different modes of inhibition: covalent-adduct formation at early times and inhibition due to cyanide generated at the active site. Separate K14CN binding studies with dopamine beta-hydroxylase corroborated the latter suggestion since 2 mol of cyanide were bound per tetramer. Tyramine stabilized [14C]cyanide binding to dopamine beta-hydroxylase, consistent with the lack of enzyme reactivation observed under certain conditions (Colombo, G., Giedroc, D. P., Rajashekhar, B., and Villafranca, J. J. 1984) J. Biol. Chem. 259, 1601-1606). EPR data for dopamine beta-hydroxylase-bound Cu2+ directly demonstrated that a quaternary complex with tyramine and cyanide was formed, since the spectrum of dopamine beta-hydroxylase-Cu2+-tyramine-cyanide is distinct from that of dopamine beta-hydroxylase-Cu2+-cyanide and dopamine beta-hydroxylase-Cu2+-tyramine. A comprehensive mechanism for dopamine beta-hydroxylase inhibition by benzyl cyanides is presented.

Acetonitriles↗
PubMed1986

Synergistic lethality induced by the combination of carbon monoxide and cyanide.

Carbon monoxide (CO) and hydrogen cyanide are recognized pyrolytic products of plastic materials in fires. Lethal blood concentrations of CO and cyanide are found in fire victims and considered to be the cause of death. However, there are reports of fire victims with sublethal concentrations of both CO and cyanide and no other attributed reason for their deaths. Thus, the purpose of this study was to investigate lethality induced by low concentrations of CO and cyanide. Male ICR mice were used in these studies. Doses of potassium cyanide (4-9 mg/kg, i.p.) were administered to animals pretreated for 3 min with either air or CO (0.63-0.66%). From these data the LD50 value of potassium cyanide (KCN) was determined in these animals pretreated with either air or CO. A significantly lower LD50 value for KCN was found in CO-pretreated animals as compared to air-pretreated animals. In another series of experiments, animals were pretreated with either saline or KCN (1.00-6.35 mg/kg, i.p.) and then placed in the chamber containing a CO atmosphere (0.325-0.375%). Ten to 20% of saline-pretreated animals were dead at the end of the monitoring period. Sublethal doses of KCN (3.5-6.35 mg/kg, i.p.) produced a synergistic lethality as compared to the saline-pretreated animals. Blood was analyzed for CO and cyanide content to determine if there were any changes that could explain this augmented lethality. There was no difference in CO or cyanide blood concentrations between these treatment groups. From these data there was demonstrated a synergistic lethality induced by the combination of CO and cyanide that could not be explained by altered CO or cyanide blood concentrations.

Animals↗
PubMed1978

The reactions of Pseudomonas cytochrome c-551 oxidase with potassium cyanide.

The binding of cyanide to both oxidized and ascorbate-reduced forms of Pseudomonas cytochrome c-551 oxidase was investigated. Spectral studies on the oxidized enzyme and its apoprotein showed that the ligand can bind to both the c and d, haem components of the molecule, and kinetic observations indicated that both chromophores reacted, under a variety of conditions, with very similar rates. Cyanide combination velocities were dependent on ligand concentration, and increasing the pH also accelerated the reaction; the second-order rate constant was estimated as approx. 0.2M-1 . s-1 at pH 7.0. The binding of cyanide to the protein was observed to have a considerable influence on reduction of the enzyme by ascorbate. Spectral and kinetic observations have revealed that the species haem d13+-cyanide and any unbound haem c may react relatively rapidly with the reductant, but the behaviour of cyanide-bound haem c indicates that it may not be reduced without prior dissociation of the ligand, which occurs relatively slowly. The reaction of reduced Pseudomonas cytochrome oxidase with cyanide is radically different from that of the oxidized protein. In this case the ligand only binds to the haem d1 component and reacts much more rapidly. Stopped-flow kinetic measurements showed the binding to be biphasic in form. Both the rates of these processes were dependent on cyanide concentration, with the fast phase having a second-order rate constant of 9.3 X 10(5) M-1 . s-1 and the slow phase one of 2.3 X 10(5) M-1 . s-1. The relative proportions of the two phases also showed a dependency on cyanide concentration, the slower phase increasing as the cyanide concentration decreased. Computer simulations indicate that a reaction scheme originally proposed for the reaction of the enzyme with CO is capable of providing a reasonable explanation of the experimental results. Static-titration data of the reduced enzyme with with cyanide indicated that the binding was non-stoicheiometric, the ligand-binding curve being sigmoidal in shape. A Hill plot of the results yielded a Hill coefficient of 2.6.

Apoproteins↗
PubMed1983

Low-spin ferric forms of cytochrome a3 in mixed-ligand and partially reduced cyanide-bound derivatives of cytochrome c oxidase.

Optical-absorption-, e.p.r.- and m.c.d. (magnetic-circular-dichroism)-spectroscopic measurements were made on liganded derivatives of oxidized and partially reduced cytochrome c oxidase. When NO was added to oxidized cyanide-bound cytochrome c oxidase, no changes occurred in the optical-absorption difference spectrum. In contrast, NO induced reduction of cytochrome a3 and formation of the nitrosylferrohaem species when the oxidized resting enzyme was the starting material. E.p.r. spectroscopy of the NO-treated oxidized cyanide-bound enzyme revealed the presence of a low-spin haem signal at g = 3.40, whereas the g = 3.02 and g = 2.0 signals of the oxidized enzyme remained unchanged. Both haem groups in this species are e.p.r.-detectable simultaneously. Examination of an identical sample by m.c.d. spectroscopy in the near-i.r. region identified two distinct low-spin species at 1565 and 1785 nm. Irradiation with white light of the NO-treated cyanide-bound sample at 10K resulted in the disappearance of the g = 3.40 e.p.r. signal and the m.c.d. signal at 1785 nm, whereas a band at 1950nm increased in intensity. When the photolysed sample was warmed to 50K and held in the dark for 15 min, the original spectrum returned. Magnetization studies of the 1785nm m.c.d. band support the assignment of this signal to the same metal centre that gives rise to the g = 3.40 e.p.r. signal. The effect of NO on the oxidized cyanide-bound enzyme was compared with that obtained when the oxidized cyanide-bound species was taken to the partially reduced state. Cytochrome a3 is e.p.r.-detectable with a g-value of 3.58 [Johnson, Eglinton, Gooding, Greenwood & Thomson (1981) Biochem. J. 193, 699-708]. Its near-i.r. m.c.d. spectrum shifts from 1950nm in the oxidized cyanide-bound enzyme to 1545nm on addition of reductant. A scheme is advanced for the structure of the cytochrome a3-CuB site that allows for cyanide binding to Fea3 and NO binding to CuB. Cyanide is the bridging ligand in the ferromagnetically coupled cytochrome a3-CuB pair of oxidized cyanide-bound cytochrome c oxidase. The bridged structure and the magnetic interaction are broken when the enzyme is partially reduced. However, when NO binds to CuB the cyanide bridge remains intact, but now the odd spins of NO and CuB are magnetically coupled.

Animals↗
PubMed1986

Cyanide stimulation of tri-N-butyltin mediated hemolysis.

The effects of tributyltin and sodium cyanide on hemolysis in human erythrocytes are described. Tributyltin has a sharp cut-off concentration for induction of hemolysis. A 5 microM concentration of tributyltin induces hemolysis and 1 microM or less does not in erythrocyte suspensions with 2.3 X 10(8) cells per ml. The kinetics for tributyltin-induced hemolysis are sigmoidal indicating a complex molecular mechanism leading to lysis. Ten mM sodium cyanide plus 1 microM tributyltin does not stimulate hemolysis rates above levels observed with 10 mM sodium cyanide alone. Five mM sodium cyanide plus hemolytic concentrations of tributyltin stimulates hemolysis rates synergistically compared with either cyanide or tributyltin alone. Ultrastructurally, hemolytic concentrations of tributyltin can be visualized in the electron microscope by osmium staining during fixation as electron-dense spheres penetrating the lipid bilayer of the erythrocyte plasma membrane. Ten mM sodium cyanide plus 25 microM tributyltin increases slightly the size of osmiophilic structures in erythrocyte membranes compared with those spheres seen in cells exposed to 25 microM tributyltin alone. Sodium cyanide is the only compound tested that stimulates tributyltin-induced hemolysis. Sodium thiocyanate, previously shown to be rapidly exchanged across erythrocyte membranes by tributyltin, reduces the rate of hemolysis. It is likely that sodium cyanide stimulates hemolysis in the presence of hemolytic tributyltin concentrations because the multimolecular, membrane-intercalated, tributyltin aggregates are transporting cyanide anion by the electrically silent, anion exchange mechanism demonstrated for other anions. It is suggested that this mechanism delivers cyanide anion to or near critical membrane sites where it is available for enzyme inhibition or cross-linking of protein sulfhydryl groups.

Cyanides↗
PubMed1994

Plasma membrane hyperpolarization by cyanide in chromaffin cells: role of potassium channels.

Exposure of rat pheochromocytoma (PC12) cells to cyanide produces elevation of cytosolic calcium, impaired Na(+)-H+ exchange, membrane lipid peroxidation and release of neurotransmitters. Since these observations suggested cyanide alters plasma membrane function, the present study examined the effect of NaCN on the membrane potential of undifferentiated PC12 cells in suspension. In PC12 cells loaded with the voltage sensitive fluorescent dye, bis-oxonol, cyanide (2.5-10 mM) elicited an immediate (within seconds), concentration related decrease in fluorescence, indicating hyperpolarization of the plasma membrane. Increasing extracellular K+ concentration to 20 mM blocked the effect of cyanide (5 mM), suggesting cyanide increased K+ efflux. Pretreatment with quinine blocked the cyanide-induced hyperpolarization, whereas glyburide had little effect, showing the hyperpolarization produced by cyanide was due to activation of Ca2+ sensitive K+ channels. Removal of Ca2+ from the media did not influence cyanide-induced hyperpolarization. However, buffering intracellular Ca2+ by loading cells with the Ca2+ chelators, Quin II or BAPTA, abolished the cyanide effect, showing cytosolic Ca2+ is a key factor. These findings suggest that cyanide mobilizes Ca2+ from intracellular stores which leads to hyperpolarization via the activation of Ca2+ sensitive K+ channels.

Animals↗