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PubMed1981

Cerebrospinal fluid cyanide after nitroprusside infusion in man.

Sodium nitroprusside (SNP) is frequently used as an hypotensive agent for clipping of intracranial aneurysms, repair of arteriovenous malformations and resection of vascular tumours. Cyanide (CN), which is its main metabolic product, has been recovered from the cerebrospinal fluid (CSF) of the rat after intravenous administration of CN, but recovery of CN from CSF after SNP has not been reported in man. Seven consenting adults were studied. Adequate premedication was provided with pentobarbitone 2 mg x kg-1 and atropine 0.4 mg one hour before operation. Anaesthesia was induced with thiopentone 8 mg x kg-1 and maintained with nitrous oxide 60 per cent with oxygen and supplemental fentanyl 0.05 mg and pancuronium 0.5-1 mg as needed. Lumbar subarachnoid, radial artery, central venous, and Foley urinary catheters were inserted. Arterial carbon dioxide tension (PaCO2) was maintained between 4.6-5.32 kPa (35-40 torr) with an Air Shields ventilator. Red cell, plasma and CSF cyanide were measured using a digital ionanalyzer before and at 30 minutes interval after infusing SNP at a rate sufficient to maintain the blood pressure at two thirds of the pre-operative level. Average total dose of SNP was 0.51 mg x kg-1. CN concentration in the red blood cells increased from 9.5 +/- 2.05 to 75.12 +/- 17.12. Plasma CN increased from 0.54 +/- 0.05 to 1.09 +/- 0.14 micrograms per cent. CSF CN increased from 0.11 +/- 0.04 to 0.72 +/- 0.07 micrograms per cent. Significant increase in red cell, plasma and CSF CN occurred five minutes after the start of SNP and returned to the preoperative level 19 hours later. Conclusion CN crosses the blood-brain barrier. Large doses of SNP in patients with neurovascular brain disorders warrants caution because cytotoxic cerebral oedema and CN encephalopathy have been described in rats after intravenous injection of sodium cyanide or exposure to hydrogen cyanide.

Adult↗
PubMed2000

Mechanism, regulation, and ecological role of bacterial cyanide biosynthesis.

A few bacterial species are known to produce and excrete hydrogen cyanide (HCN), a potent inhibitor of cytochrome c oxidase and several other metalloenzymes. In the producer strains, HCN does not appear to have a role in primary metabolism and is generally considered a secondary metabolite. HCN synthase of proteobacteria (especially fluorescent pseudomonads) is a membrane-bound flavoenzyme that oxidizes glycine, producing HCN and CO2. The hcnABC structural genes of Pseudomonas fluorescens and P. aeruginosa have sequence similarities with genes encoding various amino acid dehydrogenases/oxidases, in particular with nopaline oxidase of Agrobacterium tumefaciens. Induction of the hcn genes of P. fluorescens by oxygen limitation requires the FNR-like transcriptional regulator ANR, an ANR recognition sequence in the -40 region of the hcn promoter, and nonlimiting amounts of iron. In addition, expression of the hcn genes depends on a regulatory cascade initiated by the GacS/GacA (global control) two-component system. This regulation, which is typical of secondary metabolism, manifests itself during the transition from exponential to stationary growth phase. Cyanide produced by P. fluorescens strain CHA0 has an ecological role in that this metabolite accounts for part of the biocontrol capacity of strain CHA0, which suppresses fungal diseases on plant roots. Cyanide can also be a ligand of hydrogenases in some anaerobic bacteria that have not been described as cyanogenic. However, in this case, as well as in other situations, the physiological function of cyanide is unknown.

Agrobacterium tumefaciens↗
PubMed2004

Cyanide inhibits the Na+/Ca2+ exchanger in isolated cardiac pacemaker cells of the cane toad.

The effects of the metabolic inhibition on the activity of the Na+/Ca2+ exchanger (NCX) were studied in single isolated pacemaker cells from the cane toad. Ca2+ influx on NCX (reverse mode) was estimated by measuring the increase in intracellular calcium concentration ([Ca2+]i) in response to extracellular Na+-free solution. After application of 2 mM sodium cyanide for 3-5 min, the peak [Ca2+]i in Na+-free solution was significantly decreased from 377+/-42 nM to 260+/-46 nM, suggesting inhibition of NCX. To study Ca2+ efflux on NCX (forward mode), we recorded the tail currents on repolarization which were abolished by Ni2+ and by Na+-free solution. Cyanide decreased the amplitude of tail currents by 36+/-3%. To investigate the intrinsic properties of NCX during the metabolic inhibition, we used rapid application of caffeine to trigger sarcoplasmic reticulum Ca2+ release, which then stimulates NCX current (I(NCX) ). Both the caffeine-induced peak [Ca2+]i and the peak I(NCX) were reduced by cyanide exposure. When I(NCX) was plotted against [Ca2+], the slope of the decay phase was decreased in the presence of CN- to 44+/-8% of control, indicating that for a given [Ca2+]i there was less I(NCX) produced. These results show that cyanide (CN-) inhibits NCX activity at least partly through changes in the intrinsic properties of NCX. The inhibition of NCX probably contributes to the slower firing rate of pacemaker cells in CN-.

Action Potentials↗
PubMed2005

Axial ligation and polypeptide matrix effects on the reduction potential of heme proteins probed on their cyanide adducts.

The enthalpic and entropic changes accompanying the reduction reaction of the six-coordinate cyanide adducts of cytochrome c, microperoxidase-11 and a few plant peroxidases were measured electrochemically. Once the compensating changes in reduction enthalpy and entropy due to solvent reorganization effects are factorized out, it is found that cyanide binding stabilizes enthalpically the ferriheme following the order: cyochrome c > peroxidase > microperoxidase-11. The effect is inversely correlated to the solvent accessibility of the heme. Comparison of the reduction thermodynamics for the cyanide adducts of cytochrome c and plant peroxidases with those for microperoxidase-11 and myoglobin, respectively, yielded an estimate of the consequences of protein encapsulation and of the anionic character of the proximal histidine on the reduction potential of the heme-cyanide group. Insertion of the heme-CN group into the folded peptide chain of cyt c induces an enthalpy-based decrease in E degrees ' of approximately 100 mV, consistent with the lower net charge of the oxidized as compared to the reduced iron center, whereas a full imidazolate character of the proximal histidine stabilizes enthalpically the ferriheme by approximately 400 mV. The latter value should be best considered as an upper limit since it also includes some solvation effects arising from the nature of the protein systems being compared.

Cyanides↗
PubMed1989

Voltammetric determination of cyanide and thiocyanate in small biological samples.

Practical methods for the quantitative measurement of cyanide and thiocyanate content in small biological samples are presented. The basis of the procedures is electrochemical determination of CN- with a silver rotating disk electrode at 90 mV, relative to the Ag/AgCl reference electrode, or with a dropping mercury electrode in differential pulse mode at -240 mV. Thiocyanate is oxidized to CN- with permanganate under controlled conditions prior to its analysis. Endogenous cyanide and cyanide from SCN- oxidation are recovered, separately, by volatilization and trapping. Emphasis is placed on careful handling of specimens prior to analysis. Precautions include a provision for sequestering cyanide in storage, the use of an antioxidant, and an avoidance of the spontaneous sulfide formation from proteins that occurs in even mildly alkaline solutions.

Cyanides↗
PubMed1977

Involvement of iron in the biogenesis of the cyanide-insensitive respiration in the yeast Saccharomycopsis lipolytica.

The involvement of iron in the biogenesis of the cyanide-insensitive respiration in the yeast Saccharomycopsis lipolytica has been established on the following basis: (1) endogenous metal chelation by either benzyl- or salicylhydroxamic acid, EDTA or nitrilotriacetate prevented the biogenesis of the cyanide-insensitive respiratory pathway in S. lipolytica. (2) Addition of Fe(III) during the biogenesis increased both the rate of the appearance of the alternative respiratory pathway and its extent. Neither Fe(II), nor Co(II), Cu(II), Al(III), La(III), Mn(II) or Mg(II) could substitute for Fe(III). (3) The biogenesis of the alternative respiratory pathway could be dissociated into two steps: (a) a first one, slow, cycloheximide-sensitive, temperature-dependent, iron-independent, leading to cells still fully cyanide-sensitive, presumably involving the de novo biosynthesis of an inactive protein moiety and (b) a second step, fast, iron-dependent, temperature-independent, cycloheximide-insensitive, leading to cells with a cyanide-insensitive respiration, presumably the activation by iron of the inactive precursor.

Chelating Agents↗
PubMed1980

Chloramphenicol-induction of a second cyanide-and azide-insensitive mitochondrial pathway in Ustilago maydis.

Growth of wild type Ustilago maydis in presence of chloramphenicol results in increased resistance of cyanide-insensitive respiration to hydroxamic acid derivatives. The biphasic nature of the Dixon plots for hydroxamate inhibition of mitochondrial alternative respiration suggested involvement of two cyanide-sensitive systems. This hypothesis was confirmed by the analysis of kinetic data. One of the two systems exhibits normal sensitivity to hydroxamates and appears similar to that present in mitochondria from cells grown in control medium. In contrast, the inducible system is characterised by resistance to hydroxamates and lower substrate affinity. With excess substrate and AMP in reaction mixutre the two systems have equal participation in the cyanide-insensitive respiration of chloramphenicol-treated mitochondria. In the absence of AMP, however, the inducible oxidase seems to exhibit much higher affinity for oxygen. The new system appears responsible also for changes in sensitivity of alternative respiration to low temperatures. It differs from the hydroxamate resistant systems recently reported for other fungi in its high activity and its complete insensitivity to azide and cyanide.

Adenosine Monophosphate↗
PubMed1986

Discrimination between duroquinol oxidase activity and the terminal oxidation step of the cyanide-resistant electron transport pathway of plant mitochondria.

Comparison of the cyanide-resistant duroquinol oxidase activity of sub-mitochondrial particles from Arum maculatum L. with their ability to carry out a cyanide-resistant oxidation of NADH and succinate shows that heat-inactivation of the duroquinol oxidase activity does not proportionally affect NADH and succinate oxidation. Moreover, 1 microM antimycin inhibits duroquinol oxidase activity by 50% while not decreasing the rates of NADH and succinate oxidation. Therefore, the cyanide-resistant electron transport does not appear to be mediated by a "duroquinol oxidase", and a convincing proof of the existence of a specific protein acting as a cyanide-resistant oxidase in plant mitochondria is still lacking.

Antimycin A↗
PubMed1990

Cyanide resistant respiration is involved in temperature rise in ripening mangoes.

Thermogenesis is attributed to the cyanide resistant respiration in the inflorescence of Arum lilies. Although cyanide resistant respiration is ubiquitously operative in the plant systems, it has never been correlated with thermogenesis except for the above example. Internal temperature of the ripening mango increased from 29.0 degrees C to 38.9 degrees C during its ripening process. Concomitantly, it was coupled with the increase in total respiration and cyanide resistant respiration as well. Implication of cyanide resistant respiration in thermogenesis has been discussed in relation to the ripening fruit.

Carbohydrate Metabolism↗
PubMed1994

Glucocorticoids increase extracellular [3H]D-aspartate overflow in hippocampal cultures during cyanide-induced ischemia.

Glucocorticoids (GCs), the adrenal steroid hormones secreted during stress, exacerbate neuronal death in the hippocampus during ischemia. Since ischemia brain damage is ascribed to an elevated level of extracellular excitatory amino acids (EAAs), this study was undertaken to investigate the effect of GCs on EAA homeostasis in hippocampal cell cultures during the insult of cyanide exposure. Using D-[2,3-3H]aspartic acid ([3H]D-Asp) as a tracer, we found that corticosterone (CORT, the physiological GC in rats) increased the accumulation of extracellular [3H]D-Asp by 25% in hippocampal cultures during cyanide-induced ischemia. CORT had no effect on the release of [3H]D-Asp. Instead, analysis of [3H]D-Asp uptake kinetics indicates that CORT decreased the maximum uptake rate and the Michaelis constant by 44% and 50%, respectively, in cells treated with cyanide. It is concluded that, during cyanide-induced ischemia, CORT might enhance extracellular overflow of [3H]D-Asp by decreasing its uptake, thereby endangering neurons.

Animals↗
PubMed1990

Essential role of ferrous iron in cyanide-resistant respiration in Hansenula anomala.

Antimycin A-dependent induction of cyanide-resistant respiration in Hansenula anomala was completely blocked by o-phenanthroline, alpha,alpha'-dipyridyl, or 8-hydroxyquinoline. Pulse-labeling of the cells with [35S]methionine in the presence of both antimycin A and o-phenanthroline indicated that the 36-kDa protein previously reported to be involved in cyanide-resistant respiration [(1989) J. Biochem. 105, 864-866] was formed in mitochondria even under these conditions. The addition of Fe2+, but not Fe3+, ions to these cells in the presence of cycloheximide resulted in the rapid expression of cyanide-resistant respiration activity. These results suggest that in the presence of both antimycin A and o-phenanthroline an inactive form of the 36-kDa protein was formed and Fe2+ ions converted it to the active form. It is also likely that Fe2+ ions are involved in the reaction mechanism of cyanide-resistant respiration.

2,2'-Dipyridyl↗
PubMed1992

Possible involvement of superoxide anion in the induction of cyanide-resistant respiration in Hansenula anomala.

A chemiluminescence study showed that Qi site inhibitors such as antimycin A induce O2- generation in respiring cyanide-sensitive mitochondria from the yeast, Hansenula anomala. The O2- generation was suppressed by radical scavengers such as flavone, butylated hydroxyanisole, and Co0. Induction of cyanide-resistant respiration in H. anomala cells by Qi site inhibitors was also inhibited by these radical scavengers. Furthermore, antimycin A-induced synthesis of the mitochondrial 36-kDa protein, which is thought to be the alternative oxidase functional in the cyanide-resistant respiratory pathway, was abolished by the addition of flavone. These observations suggest that O2- is somehow involved in the induction of cyanide-resistant respiration.

Anions↗
PubMed1993

Cyanide-reactive sites in cytochrome bd complex from E. coli.

Cyanide reacts with cytochrome bd from E. coli in an 'aerobically oxidized' state (mainly, an oxygenated complex b558(3+) b595(3+) d(2+)-O2), bringing about (i) decomposition of the heme d2+ oxycomplex (decay of the 648 nm absorption band) and (ii) extensive red shift in the Soret region accompanied by minor changes in the visible range assigned to ferric heme b595. MCD spectra show that the Soret red shift is associated with heme b595(3+) high-to low-spin transition. This is the first unambiguous demonstration that heme b595 can bind exogenous ligands. No reaction of cyanide with b558 is observed. In about 70% of the enzyme which forms the cyano complex, the spin-state transition of b595 decay of heme d oxycomplex match each other kinetically (keff ca. 0.002 s-1 at 50 mM KCN, pH 8.1, 25 degrees C). This points to an interaction between the two hemes. The concerted binding of cyanide to d3+ and b595(3+), perhaps as a bridging ligand, is probably rate-limited by d2+ oxycomplex autoxidation. In the remaining 30% of the isolated bd, there is a rapid phase of cyanide-induced b595 spin-state transition which can be tentatively assigned to that proportion of the enzyme in which heme d is initially in the ferric rather than ferrous-oxy form.

Binding Sites↗
PubMed1992

Blockade of N-methyl-D-aspartate receptors prevents cyanide-induced neuronal injury in primary hippocampal cultures.

Cyanide-induced alterations of cytosolic calcium levels and cytotoxicity were examined in primary cultures of rat hippocampus. Cytosolic free Ca2+ ([Ca2+]i) levels were measured in hippocampal neurons using the fluorescent probe, fura 2. A concentration-dependent rise in [Ca2+]i occurred rapidly following exposure of cells to 0.5-10 mM NaCN. In normal medium (1.3 mM Ca2+), 2 mM NaCN produced an increase in [Ca2+]i (172 +/- 27% of control), 45 sec following exposure. Ca2+ elevation produced by NaCN was blocked by removal of Ca2+ from the external medium or by pretreatment with the N-methyl-D-aspartate (NMDA) receptor antagonist, 2-amino-5-phosphonovalerate (APV). The cytotoxicity of cyanide, assessed by measuring the efflux of lactate dehydrogenase, was blocked by APV. These results indicate that in hippocampal neurons, cytosolic Ca2+ accumulation induced by cyanide originates from the extracellular compartment and the NMDA receptor ionophore is a significant route for Ca2+ entry. It is proposed that excitotoxic mechanisms may contribute to altered neuronal homeostasis and injury associated with cyanide.

2-Amino-5-phosphonovalerate↗
PubMed1985

Activation of sodium cyanide to a toxic but non-mutagenic metabolite in Salmonella typhimurium.

Salmonella typhimurium strains (OASS-positive) synthesize a toxic but non-mutagenic metabolite from cyanide and O-acetylserine. Salmonella typhimurium mutant DW379 (OASS-deficient) is neither able to carry out this reaction in vitro nor produce the toxic metabolite in vivo. L-Cysteine reverses the cyanide metabolite mediated inhibition and thus allows OASS-positive strains to grow in medium containing cyanide and O-acetylserine. The results suggest that the enzyme O-acetylserine sulfhydrylase catalyzes the reaction of cyanide and O-acetylserine to form the toxic metabolite. This metabolite is ninhydrin-positive, adheres strongly to the cation-exchange column, and migrates in TLC to an Rf value similar to that of beta-cyanoalanine.

Biotransformation↗
PubMed1986

Inhibitors of the mitochondrial cytochrome b-c1 complex inhibit the cyanide-insensitive respiration of Trypanosoma brucei.

The cyanide-insensitive respiration of bloodstream trypomastigote forms of Trypanosoma brucei (75 +/- 8 nmol O2 min-1(mg protein)-1) is completely inhibited by the mitochondrial ubiquinone-like inhibitors 2-hydroxy-3-undecyl-1,4-naphthoquinone (UHNQ) and 5-n-undecyl-6-hydroxy-4,7-dioxobenzothiazole (UHDBT). The Ki values for UHDBT (30 nM) and UHNQ (2 microM) are much lower than the reported Ki for salicylhydroxamic acid (SHAM) (5 microM), a widely used inhibitor of the cyanide-insensitive oxidase. UHNQ also stimulated the glycerol-3-phosphate-dependent reduction of phenazine methosulfate, demonstrating that the site of UHNQ inhibition is on the terminal oxidase of the cyanide-insensitive respiration of T. brucei. These results suggest that a ubiquinone-like compound may act as an electron carrier between the two enzymatic components of the cyanide-insensitive glycerol-3-phosphate oxidase.

Animals↗
PubMed1985

Unique cyanide nitrogen-15 nuclear magnetic resonance chemical shift values for cyano-peroxidase complexes. Relevance to the heme active-site structure and mechanism of peroxide activation.

Cyanide ion has been utilized to probe the heme environment of the ferric states of horseradish peroxidase, lactoperoxidase and chloroperoxidase. The 15N-NMR signal for cyanide bound to these enzymes is located in the downfield region from 578 to 412 ppm (with respect to the nitrate ion reference). The corresponding signal for met-forms of hemoglobin, myoglobin and cytochrome c is much further downfield in the 1047-847 ppm region. The signal position for peroxidases is quite invariant with pH in the physiological ranges. The upfield bias for peroxidase chemical shifts must reflect unique trans iron(III) ligand types and/or proximal-group hydrogen bonding or steric effects. Model compound studies reveal a significant upfield cyanide 15N shift with addition of agents capable of hydrogen-bonding to the coordinated cyanide ion. An even more striking upfield shift of 277 ppm is associated with deprotonation of a trans imidazole residue. The distinctive chemical shifts observed for the cyano ligand in peroxidases support the hypothesis that a distal hydrogen-bonding network and perhaps a polar, basic trans ligand are essential for O-O bond activation by peroxidases.

Animals↗
PubMed1986

Proton and nitrogen-15 NMR studies of ferricytochrome c cyanide complexes: remarkable conservation of the heme environment among organisms of diverse origin.

The native ferric and cyanide-bound ferric forms of nine vertebrate and two yeast cytochromes c have been investigated by high-resolution proton nuclear magnetic resonance spectroscopy. Spectral comparisons have been made among the cytochromes with emphasis on the signal positions for heme and amino acid ligand protons. Consistent with earlier more limited studies of native ferric cytochromes c, the paramagnetically shifted proton NMR signals show little variation among species with up to 50% substitution of amino acids. Proton NMR spectra for the cyanide complexes also show little variation among species. The nitrogen-15 signal for the coordinated cyanide ion is known to be highly variable among other hemoproteins, but the signal covers a range of only 855 to 865 ppm (nitrate ion reference) for vertebrate cytochromes c and 884 to 886 ppm for yeast cytochromes c. The cyanide ligand probe thus reports an amazing conservation of the heme and proximal ligand environment among the cytochromes. Comparative proton and nitrogen-15 chemical shift values are consistent with a slightly stronger proximal histidine imidazole hydrogen bond to an amino acid carbonyl function than is the case for hemoglobin and myoglobin.

Animals↗