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PubMed1999

The lack of transplacental movement of the cyanide antidote thiosulfate in gravid ewes.

UNLABELLED: A previous study reported that the co-infusion of IV sodium thiosulfate (STS) with sodium nitroprusside (SNP) to near-term gravid ewes prevented both maternal and fetal cyanide toxicity. We questioned whether maternally administered STS crossed the ovine placenta to enhance fetal transulfuration of cyanide, or whether the fetus was dependent on maternal detoxification of cyanide after diffusion of cyanide into the maternal circulation. Ten anesthetized, near-term gravid ewes underwent hysterotomies with delivery of fetal heads for venous catheterization. Five control ewes received IV isotonic sodium chloride solution, whereas five experimental ewes received IV STS (50 mg/kg over 15 min). Serial plasma thiosulfate concentrations in ewes and fetuses were measured over 135 min. Areas under the time-plasma thiosulfate concentration curves were calculated for experimental and control ewes at 2758+/-197 and 508+/-74 min x mg(-1) x L(-1), respectively (P < 0.008). Mean areas under the curve for experimental and control fetuses were 236+/-34 and 265+/-23 min x mg(-1) x L(-1), respectively (P > 0.5). Maternally administered STS may prevent fetal cyanide poisoning from SNP administration without relying on STS crossing the placenta into the fetal circulation. Fetal cyanide may cross down a concentration gradient from fetal to maternal circulation, to be transulfurated to thiocyanate in maternal tissues. IMPLICATIONS: We evaluated the mechanism of action of sodium thiosulfide (STS) in sodium nitroprusside-induced cyanide toxicity in the ewe. Fetal cyanide poisoning is alleviated by maternal administration of STS, although this cyanide antidote apparently does not cross the placenta.

Animals↗
PubMed1977

Cyanide release from sodium nitroprusside in the dog.

Thirty-nine dogs (including eight from a previous study) were given during a one-hour infusion either low (less than 1.0 mg/kg) or high doses (greater than 1.0 mg/kg) of sodium nitroprusside in the presence or absence of circulating methemoglobin. In animals given low doses, the metabolic effects were relatively mild and consistent with those accounted for by a reduction in arterial pressure to 40 torr. In animals given high doses (with the same arterial pressure), metabolic alterations were significantly magnified and oxygen extraction was decreased. Animals pretreated with methemoglobin and given high doses of nitroprusside (again at the same arterial pressure) showed no toxic effect of nitroprusside. In separate studies, blood and tissue levels of cyanide were measured in dogs given high doses of nitroprusside (2.5-3.5 mg/kg) in the presence or absence of methemoglobin. In dogs given methemoglobin, 60 per cent of the administered cyanide (as nitroprusside) was recovered in the blood (as cyanmethemoglobin) after a one-hour infusion. Thereafter, blood cyanide levels declined over three hours to 25 per cent of peak levels, presumably by conversion to thiocyanate, since tissue levels of cyanide were negligible. In dogs not given methemoglobin, blood cyanide levels qualitatively followed a similar pattern but quantitatively were a fourth to a third those of pretreated dogs, and tissue levels of cyanide became elevated. It is concluded that in the dog nitroprusside, acutely administered, causes cyanide toxicity at doses exceeding 1.0-1.5 mg/kg, that the release of cyanide from nitroprusside in blood is rapid and in large quantities, that detoxification (presumably by conversion of cyanide to thiocyanate) is likewise fairly rapid but insufficient to prevent toxicity, and that protection is provided by methemoglobin.

Animals↗
PubMedDate not supplied

Cyanide poisoning in victims of fire: analysis of 364 cases and review of the literature.

Cyanide is produced by the combustion of natural and synthetic materials. It is assumed that cyanide poisoning is a major component of smoke inhalation injury; however, scientific verification of this assumption is lacking. In this study we examined blood carboxyhemoglobin and cyanide levels in fire fatalities. Carboxyhemoglobin levels of 433 fatalities averaged 44.9% and exceeded fatal (> or = 50%) levels in 195 cases. Cyanide levels of 364 fatalities averaged 1.0 mg/L and exceeded fatal levels (> 3 mg/L) in 31 cases. For victims with cyanide levels above 3 mg/L the mean carboxyhemoglobin level was 62.5%. Cyanide poisoning is infrequent in fire fatalities, and when present it is associated with significant carboxyhemoglobinemia. Cyanide can be both produced and degraded in blood and tissue, making interpretation of blood levels difficult. In survivors of fire, detoxification of cyanide can occur without specific antidotes with the use of aggressive supportive care. Specific assay and treatment for cyanide poisoning is rarely necessary in the treatment of victims of smoke and fire.

Adult↗
PubMed1987

The contribution of intracellular acidosis to the decline of developed pressure in ferret hearts exposed to cyanide.

1. The concentrations of phosphorus-containing metabolites were measured using 31P nuclear magnetic resonance (n.m.r.) in Langendorff-perfused ferret hearts. The hearts were stimulated at a constant rate and developed pressure was measured. 2. The inhibition of oxidative phosphorylation with cyanide (2 mM) decreased developed pressure. This was accompanied by an intracellular acidosis, a fall in the concentration of phosphocreatine ([PCr]) and a rise in that of inorganic phosphate ([Pi]). 3. The effects of cyanide on developed pressure were compared with those of simply decreasing the intracellular pH (pHi) (by elevating CO2) to match the change produced by cyanide. The change of pHi alone resulted in about 33% of the decrease of force produced by cyanide. 4. The relationship between developed pressure and pHi was investigated by altering CO2. It could be described by an equation of the form:log developed pressure = a + b pHi where a and b were independent of pHi. The addition of cyanide decreased a but had no significant effect on b. In other words a given change of pHi had the same fractional effect on pressure in the absence as in the presence of cyanide. 5. In another series of experiments, after cyanide had been added, pHi was returned to control levels by decreasing CO2. This increased developed pressure. Nevertheless the pressure was still considerably less than in control. Furthermore, if the acidosis was abolished by decreasing CO2 at the same time as cyanide was added developed pressure still decreased. 6. We conclude that most of the decrease of developed pressure produced by cyanide is not produced by intracellular acidosis and may result from increased [Pi].

Animals↗
PubMed1996

Complexation of intracellular cyanide by hydroxocobalamin using a human cellular model.

1. The rational for administering hydroxocobalamin (OHCbl) as an antidote to cyanide poisoning is based on the high affinity of CN ion for cobalt compounds. However, only few data are available on the influence of OHCbl on the intracellular cyanide pool. 2. In human fibroblasts incubated for 10 min with 500 microM of [14C] cyanide, the accumulation ratio was 25 at 37 degrees C (10.45 +/- 1.51 mM) and 11.9 at 4 degrees C. 3. Using the monoblastic U-937 cell line, a rapid uptake of radioactive cyanide was observed with a maximum accumulation ratio of 1.97 at 5 min. 4. A linear relationship between cyanide uptake by U-937 cells and cyanide concentration in incubation medium (10-500 microM; 5 min) was found suggesting a first order process (k = 0.25 min-1). 5. After incubation of fibroblasts with 500 microM of OHCbl, a 75% decrease of intracellular cyanide was observed, with concomittant formation of intracellular cyanocobalamin CNCbl (intracellular/extracellular ratio: 158). 6. These findings suggest that OHCbl is able to penetrate into heavily cyanide loaded cells and to complex cyanide to the non-toxic CNCbl form.

Antidotes↗
PubMedDate not supplied

Upflow anaerobic sludge blanket treatment of starch wastewater containing cyanide.

Treatment of tapioca starch wastewater containing cyanide using an upflow anaerobic sludge blanket (UASB) process was investigated. Sludge from an anaerobic lagoon treating tapioca starch wastewater was used as seed. Performance of the UASB reactor with influent cyanide concentrations up to 25 mg/L was assessed. The inhibitory effects of cyanide were temporary and reversible. The process required longer recovery period for higher cyanide dosage. For 25 mg/L of cyanide concentration in the feed, the reactor required 15 days for complete recovery. Process performance was sensitive to operating parameters such as upflow velocity, cyanide loading rate, and chemical oxygen demand (COD) loading rate. A maximum cyanide loading rate of 0.38 kg/m3 x d was achieved in the process at a COD loading rate of 50 kg COD/m3 x d. Experiments with tapioca starch wastewater containing up to 10 mg/L of cyanide yielded satisfactory cyanide removal of approximately 93 to 98% and gas productivity of 7.5 m3/m3 x d with a COD loading rate of 30 to 40 kg COD/m3 x d.

Bacteria, Anaerobic↗
PubMed2000

Development of a method for determination of cyanide concentrations in serum and rumen fluid of cattle.

OBJECTIVES: To develop a reliable method for measurement of cyanide concentrations in cattle, using gas chromatography-mass spectrometry (GC-MS), and establish reference ranges of cyanide concentrations in cattle. ANIMALS: 52 Fleckvieh cattle. PROCEDURE: Cattle were allocated to 3 groups; 12 were fed leguminous grass and hay, 36 were fed whole-maize and corn-cob silages, and 4 were fed other feedstuffs. Samples of blood, rumen fluid, and liver were collected at time of slaughter. Serum, rumen fluid, and liver homogenate were assayed for cyanide content, using a derivatization procedure. A technique for analysis by GC-MS that used selected ion monitoring was developed. RESULTS: Compared with a spectrophotometric method, detection of cyanide in serum and rumen fluid by use of GC-MS was selective and sensitive, with a limit of detection of 0.7 microM. Spectrophotometric analysis yielded false-negative and false-positive results. Thus, the GC-MS method was used for subsequent analysis. In all cattle except 1, cyanide concentration ranged from < 0.7 to 35 microM in serum and from < 0.7 to 28 microM in rumen fluid; cyanide concentration in that 1 animal was 206 microM. Cattle fed clover, grass, grass hay, and clover hay had 8.3- to 8.6-fold higher mean cyanide concentrations in rumen fluid and serum than cattle fed whole-maize and corn-cob silages. CONCLUSIONS AND CLINICAL RELEVANCE: Results of this study suggest a reference range that should be useful for aiding in the diagnosis of cyanide poisoning. Also, cattle can apparently accommodate a serum cyanide concentration of 206 microM without adverse effects.

Animal Feed↗
PubMed2000

Intact smooth muscle metabolism: its responses to cyanide poisoning and pyruvate stimulation.

Smooth muscle mitochondria are unique in their compartmentalization of metabolism with the contractile proteins and putative role in cell fate choice. In this study we examine the relative and quantitative differences that smooth muscle mitochondria have with regard to cyanide inhibition. The effect of cyanide poisoning in the mitochondria of smooth muscle was examined in the intact porcine carotid artery and intact guinea pig stomach. The respiratory responses of these tissues were monitored in the presence of cyanide and following the addition of various metabolites. In HEPES buffer with 10 mM glucose as the substrate, it was found that the EC50 for cyanide inhibition was 0.11+/-0.02 and 0.14+/-0.02 mM in the pig carotid and guinea stomach respectively. We also found that the signaling metabolite, pyruvate could partially reverse this inhibition. With pyruvate (10 mM) as the substrate, the EC50 increased significantly to 6.52+/-0.11 (carotid artery) and 1.95+/-0. 30 (stomach) mM as well as being significantly different between the tissues. This apparent resistance to cyanide inhibition caused by pyruvate was lost when sodium bicarbonate buffer was used (EC50 in the presence of pyruvate of 0.13+/-0.04 and 0.25+/-0.04 for carotid and stomach respectively). HEPES buffer permitted pyruvate's protection from cyanide poisoning whereas bicarbonate buffer did not. The rate of respiration caused by pyruvate re-stimulation was not significantly different than control in the stomach (2.63+/-0.77 and 2.69+/-0.3??Mol O2/min/g dw respectively) but was significantly greater in the carotid artery. Therefore, smooth muscle with 10 mM pyruvate and 1 mM cyanide had a rate or respiration significantly greater than with 10 mM glucose alone (0.90+/-0.2 and 0.59+/-0. 06??Mol O2/min/g dw respectively). Using 31P NMR spectroscopy, we observed a complete normalisation of high energy phosphates and pH in the guinea pig stomach smooth muscle caused by pyruvate after cyanide poisoning. These results suggest that cyanide's toxicity of smooth muscle oxidative metabolism is affected by the buffer (HEPES versus Bicarbonate) and metabolic signalling molecules or substrates (pyruvate versus glucose) in which the tissues are exposed to as well as tissue to tissue variations.

Animals↗
PubMed1991

Acetonitrile serum concentrations and cyanide blood levels in a case of suicidal oral acetonitrile ingestion.

Acute acetonitrile toxicity is mainly dependent on the release of cyanide via hepatic metabolism. Although evaluated in animals, few data are available concerning the toxicokinetic parameters of acetonitrile and acetonitrile-liberated cyanide in human. This paper reports a case of suicidal oral acetonitrile ingestion of about 5 mL without severe symptoms of intoxication in a previously healthy adult male with a body weight of 60 kg. Acetonitrile serum concentrations as well as cyanide blood levels were determined over the whole hospitalization. The elimination half-lives calculated from these data were 32 h for acetonitrile and 15 h for cyanide. After sodium thiosulfate bolus application, the cyanide blood level rapidly decreased to 10% of the initial value, indicating that sodium thiosulfate sufficiently detoxifies acetonitrile-liberated cyanide. Since cyanide levels again increased to maximal values about 4.5 h after sodium thiosulfate application, continued thiosulfate therapy is required as predicted by the long elimination half-lives of acetonitrile and acetonitrile-liberated cyanide. Determination of cyanide and acetonitrile concentrations is recommended for the estimation of optimal individual sodium thiosulfate dosage.

Acetonitriles↗
PubMed1999

Development and activation of cyanide-resistant respiration in the yeast Yarrowia lipolytica.

Changes in respiratory activity and in the contents of adenine nucleotides (ATP, ADP, AMP) were studied in cells of the yeast Yarrowia lipolytica during the development of cyanide-resistant respiration. The transition of the yeast from the logarithmic to the stationary growth phase due to exhaustion of glucose was associated with decreased endogenous respiration and with the activation of a cyanide-resistant oxidase. Cyanide activated cell respiration during the stationary growth phase. The cyanide-resistant respiration was inhibited by benzohydroxamic acid (BHA), an inhibitor of the alternative oxidase. In the absence of cyanide, BHA had no effect on the cells which had the cyanide-resistant oxidase. This indicates that the cells do not use the alternative pathway in vivo. The decreased endogenous respiration of the cells was accompanied by decreased contents of adenine nucleotides. Addition of cyanide resulted in a sharp decrease in the content of ATP, in a twofold increase in the content of ADP, and in a fivefold increase in the content of AMP. In the absence of cyanide, BHA had virtually no effect on the contents of adenine nucleotides. The decreased rate of oxygen consumption during the transition of the cells to the stationary growth phase was caused by the decreased activity of the main cytochrome-containing respiratory chain (2,4-dinitrophenol (DNP) stimulated respiration). The alternative oxidase was synthesized in the cell but was inactive. Cyanide stimulated respiration due to activation of the alternative oxidase via the AMP produced. The decrease in the cell content of ATP is suggested to be a factor inducing the synthesis of the alternative oxidase.

2,4-Dinitrophenol↗
PubMed1979

[Cyanide-resistant respiration of Pseudomonas aeruginosa bacteria].

The transition of the bacterial culture into the stationary growth phase is accompanied by an appearance of cyanide-resistant respiration. Chloramphenicol inhibits the development of cyanide-resistant respiration. The cyanide-resistant oxidase is localized in the bacterial membrane. Its appearance is not due to the quantitative and qualitative changes of flavins, non-heme iron, ubiquinone and cytochromes of the b and c types, but is accompanied by an increase in the copper content of the membrane preparations. Neither cyanide-sensitive, nor cyanide-resistant chains of the bacterial electron transfer contain cytochromes of the a type. The cyanide-resistant oxidase accepts electrons at the ubiquinone--cytochrome b level of the main respiratory chain. The cyanide-resistant respiration is not accompanied by a formation of hydrogen peroxide. Cytochrome o performs the function of cyanide-sensitive oxidase. The nature of cyanide-resistant oxidase still remains obscure.

Cyanides↗
PubMed1977

Determination of cyanide and nitroprusside in blood and plasma.

A procedure was refined for quantitative isolation of cyanide by gas transfer from acidified blood or plasma samples. The cyanide was trapped in dilute alkali and quantified as the pyridine/pyrazolone complex. The within-day coefficient of variation was 2%, which increased to about 2.5% for the day-to-day variation. Nitroprusside used as a hypotensive agent in clinical medicine provides a risk of cyanide toxicity when the rate of administration or the total amount of drug given is excessive. A procedure was developed for measuring nitroprusside in the plasma of man and animals. Nitroprusside in the sample is quantitatively converted to cyanide by incubation with cystein solution at slightly alkaline pH. Methemoglobin is added to combine with the cyanide formed and prevent its destruction. On acidification, the total amount of cyanide originally present as free cyanide or as nitroprusside is liberated as HCN, isolated by gas transfer into a sodium hydroxide trap, and quantified by spectrophotometry. Nitroprusside present in the sample is calculated from the increase in cyanide observed in the cysteine-treated sample compared to that obtained without cysteine treatment. The method has been used to estimate in vitro stability of nitroprusside in aqueous solution, blood, and plasma. Blood cyanide and plasma nitroprusside concentrations were measured when sodium nitroprusside was infused into a baboon. Over 90% of the nitroprusside in blood is present in the plasma, suggesting that the drug crosses the erythrocyte membrane slowly.

Analysis of Variance↗
PubMedDate not supplied

[Cyanide-resistant respiration in Torulopsis candida].

The effect of cyanide and the inhibitors of cyanide-resistant oxidase--hydroxamic acids on endogenous respiration and oxidation of a number of substrates by Torulopsis candida resting cells taken at different stages of growth on glucose and hexadecane was studied and made it possible to arrive at the following conclusions. 1. The effect of cyanide on endogenous respiration of T. candida differs during its growth on glucose and hexadecane. On hexadecane, irrespective of the growth phage, cyanide inhibits endogenous respiration by 70--75%. On glucose, cyanide inhibits endogenous respiration not more than by 35% and only at the exponential growth phase whereas it stimulates endogenous respiration in the course of other growth stages. 2. The effect of cyanide on respiration of the resting cells of T. candida which oxidize glucose, hexadecane, primary alcohols and tetradecanoic acid hardly depends on the growth stage. It is determined mainly by the nature of a substrate to be oxidized. 3. Hydroxamic acid have no effect on the cell respiration in the absence of cyanide. However, in its presence, they entirely inhibit both endogenous respiration and oxidation of the aforementioned substrates. 4. Under almost all above experimental conditions, the sensitivity of cell respiration to cyanide changes only slightly at different stages of growth on either glucose or hexadecane. This feature markedly distinguishes T. candida among other cyanide-resistant yeasts.

Candida↗
PubMed1995

Antagonism of relaxing responses to nitrovasodilators by cyanide in rabbit isolated aortic preparation.

Effect of sodium cyanide on the relaxing response (decrease of intraluminal pressure) to sodium nitroprusside, sodium nitrite, nitric oxide and human atrial natriuretic peptide (HANP) was investigated in isolated rabbit aortic preparations in vitro. Cyanide 1 microM approximately 1 mM produced relaxation in norepinephrine (NE) 1 microM-contracted aortic preparation in a concentration dependent manner. Cyanide 100 microM, which was administered approximately 8 min before NE addition, depressed the relaxing response to nitroprusside 0.1 microM in NE 1 microM-contracted aortic preparation. The relaxing responses to nitric oxide 0.3 and 3.3 microM were slightly, but concentration-dependently depressed by cyanide 1-100 microM, which was administered 6-10 min before nitric oxide addition, in NE 1 microM-contracted aortic preparations. Cyanide 100 microM and 1 mM, which was administered 4-10 min after nitroprusside 0.1 microM, reversed the nitroprusside-induced relaxation in NE 1 microM contracted aortic preparation. Namely, relaxing response of NE-contracted aortic preparation to cyanide was converted into contractile response in the presence of nitroprusside. Similar reversal phenomena of the responses to cyanide 100 microM and 1 mM were also observed in the presence of sodium nitrite 0.1 microM or nitric oxide 3.3 microM, but those were less extent than that of nitroprusside 0.1 microM. On the contrary, the relaxing response to cyanide 100 microM was unaffected by pretreatment with HANP 0.37 nM. These findings may indicate that cyanide inhibits soluble guanylate cyclase activated by nitroprusside, sodium nitrite or nitric oxide through interaction with nitric oxide and heme binding site of the enzyme.

Animals↗
PubMed1979

The reaction of carbonyl cyanide phenylhydrazones with thiols.

Carbonyl cyanide phenylhydrazone and its ring-substituted analogs react with thiols (thioglycolic acid, 2-mercaptoethanol, dithiothreitol) and aminothiols (cysteine, glutathione) to give corresponding N-(substituted phenyl)-N'-(alkylthiodicyano)-methylhydrazine derivatives. These addition products decompose to the original components in alkaline solution. On the other hand, in the presence of an excess of thiols in aqueous buffered systems the addition reactions are practically quantitative with respect to phenylhydrazones, follow pseudo-first-order kinetics and can be investigated spectrophotometrically. These reactions are of the bimolecular AdN type where the non-dissociated form of carbonyl cyanide phenylhydrazones function as an electrophilic component, while the RS- ion plays the role of nucleophilic component in the case of thiols (the attack of the azomethine group). The reactivitiy of carbonyl cyanide phenylhydrazones with respect to thiols increases in the order carbonyl cyanide phenylhydrazone less than carbonyl cyanide m-chlorophenylhyrazone less than carbonyl cyanide p-trifluoromethoxyphenylhydrazone which corresponds to the order of decreasing values of the pKa constants. On the other hand, the reactivity of thiols increases with their basicity. The reactivity of carbonyl cyanide phenylhydrazone with thiols is comparable with the reactivity of phenyl isothiocyanate and N-ethylmaleimide. It was demonstrated that carbonyl cyanide phenylhydrazone is an efficient inhibitor of rabbit muscle glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.12). The results obtained are discussed in relation to the biological activity of carbonyl cyanide phenylhydrazones.

Animals↗
PubMed1996

Vibrational Analysis of a Molecular Heme-Copper Assembly with a Nearly Linear Fe(III)-CN-Cu(II) Bridge: Insight into Cyanide Binding to Fully Oxidized Cytochrome c Oxidase.

The complete vibrational analysis of [(1-MeIm)Fe(OEP)-CN-Cu(Me(6)tren)](2+) (1), which has been constructed as a model for the cyanide-ligated binuclear center in the respiratory protein cytochrome c oxidase, has been carried out. The resonance Raman spectra (lambda(exc) = 647 nm) and the mid-infrared spectra display three cyanide isotope-dependent vibrational modes. Two vibrations showed monotonic decreases with increasing mass of the cyanide ligand (2182-2137-2146-2101 cm(-)(1) and 535-526-526-520 cm(-)(1), respectively, for the (12)C(14)N-(13)C(14)N-(12)C(15)N-(13)C(15)N isotopomers), and could thus be assigned to the C&tbd1;N and Fe-CN-Cu stretching vibrations, respectively. The third vibration, detected with resonance Raman, showed a zigzag-type behavior (495-487-493-485 cm(-)(1) with the set of isotopomers above) with the frequency being more sensitive to (13)C labeling of the cyanide ligand than with (15)N labeling. This pattern of isotopic dependence is characteristic of a bending vibration. Additionally, with the same laser excitation frequency, the C&tbd1;N stretching mode was observed, which is the first time that this vibration has been detected in the resonance Raman spectrum of a synthetic heme-cyanide complex. The normal coordinate analysis showed marked differences between bridged and unbridged heme-cyanide complexes. Internal coordinates that are orthogonal in unbridged systems are significantly mixed in the bridged model, despite the overall linearity of the Fe-CN-Cu moiety. These measurements strengthen the proposal that cyanide bridges the two metal atoms in the cyanide-ligated, oxidized binuclear center of cytochrome c oxidase. A quantitative consideration of the vibrational characteristics of cyanide bound to the resting enzyme, in light of our model compound results, strongly suggests that the binuclear center is flexible and can undergo structural rearrangement to accommodate exogenous ligands. This is likely to be of mechanistic importance in both dioxygen reduction and proton translocation.

Journal Article↗
PubMed1990

Effect of 2,4-Dichlorophenoxyacetic Acid on Endogenous Cyanide, beta-Cyanoalanine Synthase Activity, and Ethylene Evolution in Seedlings of Soybean and Barley.

Treatment of etiolated seedlings of barley (Hordeum vulgare) and soybean (Glycine max) with 1 millimolar 2,4-dichlorophenoxyacetic acid (2,4-D) resulted in a 14-fold and greater than 100-fold increase in ethylene production, respectively. Simultaneous monitoring of endogenous cyanide and beta-cyanoalanine synthase (beta-CAS) (EC 4.4. 1.9) activity was also performed. Endogenous levels of cyanide did not change in barley. In soybean, endogenous cyanide increased within 3 hours, increased again 6 hours after exposure to 2,4-D, and continued to increase throughout the experimental period. The activity of beta-CAS increased in both barley and soybean 9 hours after herbicide treatment. The increase in cyanide preceded the increase in beta-CAS activity by 3 to 6 hours in soybean. The steady-state concentration of endogenous cyanide in soybean was 1 micromolar, based on rates of ethylene production and cyanide metabolism by beta-CAS. This agreed with the determination of endogenous cyanide by both distillation and isotope dilution. Given the apparent compartmentalization of beta-CAS in mitochondria and the localization of ethylene/HCN production at the plasmalemma and/or tonoplast, our results suggest that extra-mitochondrial accumulation of cyanide in the cytoplasm may occur. If so, the activity of cyanide-sensitive cytoplasmic enzymes could be adversely affected, thus possibly contributing to the toxicity of 2,4-D.

Journal Article↗
PubMed1983

Inhibition of p-nitroanisole O-demethylation in perfused rat liver by potassium cyanide.

The effect of potassium cyanide on p-nitroanisole O-demethylation in perfused rat livers has been examined. Cyanide (2 mM), an inhibitor of cytochrome oxidase, diminished p-nitroanisole O-demethylation by 50-75% in perfused livers from normal and phenobarbital-treated rats, but had much less effect on hepatic microsomal p-nitroanisole O-demethylation. The inhibition was also observed in livers where the activity of the pentose phosphate shunt was abolished by pretreatment with 6-aminonicotinamide. Cyanide infusion decreased hepatic ATP/ADP ratios and cellular concentrations of glutamate, alpha-ketoglutarate, and isocitrate, but caused an increase in the NADP+/NADPH ratio. Rates of NADPH generation via the pentose phosphate shunt were unchanged by cyanide, and hepatic concentrations of glucose 6-phosphate were markedly increased by cyanide. Thus, inhibition of p-nitroanisole metabolism could not be explained solely by a direct interaction of cyanide with mixed-function oxidases or diminished NADPH generation via the pentose cycle. These data indicate that cyanide inhibits mixed-function oxidation in intact cells by diminishing the generation of NADPH from sources other than the pentose cycle. Further, these data are consistent with the hypothesis that some NADPH for mixed-function oxidation arises from cyanide-sensitive mitochondrial sources.

Animals↗