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PubMed1999

Fourier-transform infrared studies on azide-binding to the binuclear center of the Escherichia coli bo-type ubiquinol oxidase.

Azide-binding to the heme-copper binuclear center of bo-type ubiquinol oxidase from Escherichia coli was investigated with Fourier-transform infrared spectroscopy. Deconvolution analyses of infrared spectra of the azide (14N3)-inhibited air-oxidized form showed a major infrared azide antisymmetric stretching band at 2041 cm(-1). An additional band developed at 2062.5 cm(-1) during a longer incubation. Isotope substitutions with terminally 15N-labelled azides did not show a splitting of the major band, indicating that the geometry of the bound azide is mainly in a bridging configuration between high-spin heme o and CuB. The band at 2062.5 cm(-1) showed clear splittings upon substitution with the terminally 15N-labelled azides, indicating the Cu(2+)B-N=N=N structure. Partial reduction of the oxidase with beta-NADH in the presence of azide caused an appearance of new infrared bands at 2038.5 (major) and 2009 (minor) cm(-1). The former band also showed clear splittings in the presence of the terminally 15N-labelled azides, indicating that reduction of low-spin heme b alters the structure of the binuclear center leading to the Fe(3+)o-N=N=N configuration.

Azides↗

PubMed2001

The interaction of azide with polyphenol oxidase II from tobacco.

Spectroscopy studies of absorption and circular dichroism of native PPO II and azide PPO II complex demonstrate two new absorptions at 375 nm and 500 nm after azide's binding with PPO II, which are assigned as the terminal azide to copper charge transfer transitions II(o)nb-to-copper and II(v)nb-to-copper charge transfer transitions respectively. FT-IR spectra also demonstrate that the azide binds in terminal geometry with one of type-3 coppers. The interaction between azide and PPO II is discussed. One terminal azide's binding with one type-3 copper improves the activity of PPO II and the other three azides' further binding in terminal geometry with the type-3 coppers decreases the activity. We theorize that steric hindrance of azides makes oxygen difficult to bind in the active site.

Azides↗

PubMed2000

X-ray structure of azide-bound fully oxidized cytochrome c oxidase from bovine heart at 2.9 A resolution.

Two azide ions were identified, one between the Fe and Cu atoms in the O(2)-reduction site and the other at the transmembrane surface of the enzyme, in the crystal structure of the azide-bound form of bovine heart cytochrome c oxidase at 2.9 A resolution. Two geometries, a mu-1,3 type geometry between the Fe and Cu atoms and a terminal geometry on the Fe atom, are equally possible for an azide ion in the O(2)--reduction site. The other azide molecule was hydrogen bonded to an amide group of an asparagine and a hydroxyl group of tyrosine in a mu-1,1 type geometry. The antisymmetric infrared bands arising from these azide ions, which show essentially identical intensity [Yoshikawa & Caughey (1992), J. Biol. Chem. 267, 9757-9766], strongly suggest terminal binding of the azide to Fe. The electron density of all three imidazole ligands to Cu(B) was clearly seen in the electron-density map of the azide-bound form of bovine heart enzyme, in contrast to the crystal structure of the azide-bound form of the bacterial enzyme [Iwata et al. (1995), Nature (London), 376, 660-669], which lacks one of the three imidazole ligands to Cu(B).

Animals↗

PubMed1997

The binding of azide to copper-containing and cobalt-containing forms of hemocyanin from the mediterranean crab Carcinus aestuarii.

To establish the competence of the active site of hemocyanin to acquire diverse coordination geometries, the binding of azide to three forms of a crab hemocyanin, the dinuclear cupric or met-hemocyanin, the mononuclear cupric or met-apo-hemocyanin, and the mononuclear Co(II)-substituted derivative has been studied by near-ultraviolet circular dichroism and EPR spectroscopies. The near-ultraviolet circular dichroism spectra of the various derivatives present qualitatively similar features, namely a negative peak around 335 nm in the case of the two copper-containing derivatives and a three-component pattern with the Co(II) derivative. Upon decreasing the pH from 7.0 to 5.5 a decrease of optical activity is observed with all protein samples. The characteristic CD features, attributable to N(imidazole)-to-metal and to OH -to-metal charge-transfer transitions, are strongly affected by azide binding. In particular, the intensity of the negative band exhibited by the two copper-containing protein forms decreases with the onset of a new negative feature with maximum around 400 nm diagnostic for azide-to-Cu(II) charge-transfer transitions. The visible region is affected as well, indicating that changes in the coordination sphere of copper take place. The affinity for azide of the different protein forms is higher at low pH. EPR measurements on the paramagnetic met-apo-hemocyanin derivative as a function of pH demonstrate heterogeneity in the coordination environment at low pH. In the presence of azide an increase of rhombic distortion of the EPR spectra is observed and on the basis of the identified sets of copper hyperfine features in the course of azide titration experiments two different azide bound forms of met-apo-hemocyanin can be detected. The CD and EPR data at the different pH values are consistent with a reaction scheme in which azide replaces a fourth ligand in the metal-coordination sphere, identified as a water or hydroxide molecule.

Animals↗

PubMed2002

[Neurotoxicity in sodium azide poisoning].

The effects of sodium azide administration on the central cholinergic functions were investigated utilizing mice to evaluate the neurotoxicity in the acute poisoning. Seven oral doses of the toxicant, ranging in dosage from 12.3 to 59.3 mg/kg, based upon a multiple of 1.3 x 27 mg/kg (an empirical LD50 for mice) or 27 mg/kg divided by 1.3 to calculate the lower three doses, were administered to facilitate the acute signs and to observe behavior. The behavior included locomotor activity, rectal temperature and rotarod performance which are convenient for the evaluation of central cholinergic involvement even if it may be partial, since no behavioral methods to study totally the cholinergic system have been known. Measurements of the activities of acetylcholinesterase (AChE) and choline acetyltransferase (ChAT), enzymes that hydrolyze and synthesize acetylcholine (ACh) and high-affinity choline uptake (HACU), a rate-limiting step in the synthesis of ACh, were determined in the presence of various concentrations of sodium azide in vitro. Adult (12-15 weeks) female ICR strain mice were utilized in this study. Mice were orally given sodium azide in doses from 27 to 59.3 mg/kg and appeared sedated within 5 min. Next we observed hyperpnea and dyspnea, which were followed by seizure and death for mouse groups which received more than 35.1 mg/kg. Oral administration of the sodium azide solution produced an increase in locomotor activity for the 12.3 mg/kg group and a decrease for the higher doses (ranging from 16.0 to 27.0 mg/kg). The sodium azide administration suppressed rectal temperature dose-dependently as well as rotarod performance at high doses (20.8 and 27.0 mg/kg). Such behavioral changes elicited by sodium azide administration suggest an involvement of the central cholinergic system. Sodium azide also caused a measured decrease in the activity of AChE, but an increase in the activities of ChAT and HACU, dose-dependently, in vitro. From the results obtained from the behavioral and the in vitro experiments, we concluded that acute sodium azide poisoning significantly affects the central cholinergic system.

Acetylcholine↗

PubMed1985

Diffusion of extracellular hydrogen peroxide into intracellular compartments of human neutrophils. Studies utilizing the inactivation of myeloperoxidase by hydrogen peroxide and azide.

It is well known that catalase is transformed to nitric oxide-Fe2+-catalase by hydrogen peroxide (H2O2) plus azide. In this report, we show that myeloperoxidase is also inactivated by H2O2 plus azide. Utilizing this system, we studied the presence and source of intracellular H2O2 generated by activated neutrophils. Stimulation of neutrophils with phorbol myristate acetate (PMA, 100 ng/ml) plus azide (5 mM) for 30 min completely inactivated intragranular myeloperoxidase and reduced cytosolic catalase to 35% of resting cells. This intracellular inactivation of heme enzymes did not occur in normal neutrophils incubated with either PMA or azide alone or in neutrophils from patients with chronic granulomatous disease (CDG) which cannot produce H2O2 in response to PMA. Incubation of neutrophils with azide and a H2O2 generating system (glucose-glucose oxidase) inactivated 41% of neutrophil myeloperoxidase. Glutathione-glutathione peroxidase (GSH-GSH peroxidase), an extracellular H2O2 scavenger, totally protected neutrophil myeloperoxidase from inactivation by azide plus glucose-glucose oxidase. In addition, when a mixture of normal and CGD cells was stimulated with PMA in the presence of azide, 90% of the myeloperoxidase in CGD neutrophils was inactivated. Therefore, H2O2 released extracellularly from activated neutrophils can diffuse into cells. In contrast, myeloperoxidase in normal polymorphonuclear leukocytes stimulated with PMA in the presence of azide and GSH-GSH peroxidase was 75% inactivated. Thus, the results indicate that a GSH-GSH peroxidase-insensitive pool of H2O2 is also generated, presumably at the plasma membrane, and this pool of H2O2 can undergo direct internal diffusion to inactivate myeloperoxidase.

Animals↗

PubMed1977

Effects of sodium azide on platelet function.

Sodium azide in low concentrations (0.1-10 micrometer) was found to have inhibitory effects on human platelet function. Primary aggregation induced by ADP, epinephrine, thrombin and the ionophore A 23187 was decreased. To evaluate the effect of azide apart from secondary processes, the platelets were treated with indomethacin to prevent prostaglandin/thromboxane synthesis for all inducers; in addition, effects of secreted ADP, in the case of thrombin and A 23187, was prevented by the presence of creatine phosphate plus creatine phosphokinase ADP, epinephrine and A 23187, but not thrombin-induced primary aggregates, dispersed immediately upon addition of azide. Azide powerfully inhibited dense granule secretion induced by collagen, ADP and epinephrine as measured both by 14C-serotonin secretion and as judged by secondary aggregation. Shape change induced by ADP, thrombin or A 23187 was not affected. Azide had no effect on energy metabolism. Since the aggregation experiments were performed in the presence of indomethacin, and malondialdehyde formation from arachidonic acid was not affected by azide, it seemed unlikely that the inhibition by azide of platelet function was related to inhibition of synthesis of prostaglandins and thromboxanes. It is concluded that azide exerts its effects directly on the common pathway for platelet responses.

Azides↗

PubMed2003

Photochemistry of ortho, ortho' dialkyl phenyl azides.

Phenyl azide, 2,6-diethylphenyl azide, 2,6-diisopropylphenyl azide, and 2,4,6-tri-tert-butylphenyl azide were studied by laser flash photolysis (LFP) methods. LFP (266 nm) of the azides in glassy 3-methylpentane at 77 K produces the transient UV-vis absorption spectra of the corresponding singlet nitrenes. At 77 K, the singlet nitrenes relax to the corresponding triplet nitrenes. The triplet nitrenes are persistent at 77 K and their spectra were recorded. The rate constants of singlet to triplet intersystem crossing were determined at this temperature. LFP of 2,4,6-tri-tert-butyl phenyl azide in pentane at ambient temperature again produces a singlet nitrene, which is too short-lived to detect by nanosecond spectroscopy under these conditions. Unlike the other azides, the first detectable intermediate produced upon LFP of 2,4,6-tri-tert-butyl phenyl azide at ambient temperature is the benzazirine (285 nm) which has a lifetime of 62 ns controlled by ring opening to a didehydroazepine. The results are interpreted with the aid of Density Functional Theoretical and Molecular Orbital Calculations.

Journal Article↗

PubMed1994

Spin trapping of azidyl and hydroxyl radicals in azide-inhibited rat brain submitochondrial particles.

Succinate-driven respiration in azide-inhibited rat brain submitochondrial particles (smps) produces azidyl and hydroxyl radicals that were detected by spin trapping with 5,5'-dimethyl-1-pyrroline-N-oxide (DMPO). Production of radicals required succinate and oxygen and was eliminated by heat denaturation, which indicates that radical production is a result of respiration. The concentrations of both DMPO/.OH and DMPO/.N3 were decreased by addition of catalase to the smps, which indicates that H2O2 is involved in radical production. In the absence of azide anion, DMPO/.OH was not detected in the same system, even after five additions of succinate over a period of 24 h. It is proposed that azide inhibition of cytochrome c oxidase results in increased production of superoxide, which is efficiently converted to hydrogen peroxide by membrane-bound superoxide dismutase. Hydrogen peroxide activates endogenous peroxidase to react with azide anion forming azidyl radical, which damages the peroxidase, resulting in decreased production of azidyl radical with successive additions of succinate. Hydroxyl radical is produced from the hydrogen peroxide that is not removed by peroxidase. The increased production of superoxide in the azide-inhibited system suggests that loss of cytochrome c oxidase activity can lead to increased radical production if other proteins in the respiratory chain remain active. In the azide-inhibited system, reaction of azide anion with H2O2-activated endogenous peroxidase and spin-trapping of the resulting azidyl radical is a convenient monitor of H2O2 production.

Animals↗

PubMed1983

Effects of sodium azide on phototaxis of the blue-green alga Anabaena variabilis and consequences to the two-photoreceptor systems-hypothesis.

Experiments with sodium azide support the earlier report that two different photoreceptor systems participate in the absorption of the phototactically active light in Anabaena variabilis. The one of them, represented by the phycobiliproteins and chlorophyll a, is responsible for positive and negative phototaxis around 440 nm and between 580 and 700 nm. This system is sensitive to sodium azide which is able to reverse the negative reaction at high fluence rates to a positive one. The second one which absorbs light between 500 and 560 nm and above 700 nm is insensitive to azide. It triggers only negative responses in absence and presence of azide as well. P750 is obviously not a photoreceptor pigment of this system, since there is no indication for its occurrence in Anabaena. Even photobleaching of the photosynthetic pigments at high fluence rates is prevented by azide. The noncyclic photosynthetic electron transport is not severely inhibited by azide because photokinesis is only in part impaired. Therefore, the hypothesis is suggested that the phototactic reaction-sign reversal generator of Anabaena is controlled by the level of an active oxygen species, probably singlet oxygen, which is quenched by azide.

Azides↗

PubMed1991

Sodium azide: ineffective as a faecal preservative for parasitological diagnosis.

Sodium azide was compared with 10% formalin to evaluate sodium azide's effectiveness as a faecal preservative for intestinal helminths and protozoa. Faecal specimens collected from Haiti were preserved in sodium azide and in 10% formalin and analysed after 1.5, 6.5 and 11.5 weeks by examining direct wet-mount preparations. Sodium azide did not preserve the morphology of either helminths or protozoa as well as 10% formalin did. However, sodium azide prevented embryogenesis of helminth eggs, while some helminth eggs in 10% formalin contained living larvae. Biosafety guidelines regarding the toxicity, reactivity, and disposal of sodium azide were strictly followed. Use of 10% formalin is a significantly better choice than sodium azide for preserving parasites when accurate identification of parasites and biosafety are the main concerns.

Adolescent↗

PubMed1993

Electrical responses of the rat's retinal pigment epithelium to azide and thiocyanate.

In the rat under urethane anesthesia, a fast intravenous injection of a bolus of sodium azide elicited a transient cornea-positive change in transocular potential (azide response). A bolus injection of sodium thiocyanate (NaSCN) produced a cornea-negative response (SCN- response) with a similar rising phase as the azide response, but with a faster return from the peak. The peak amplitude depended on bolus volume, concentration, animal strain, and age. For more than 24 h, the azide and SCN- responses could be recorded repeatedly from a single rat with little variation in peak amplitudes. Following an administration of iodate, known to degenerate the retinal pigment epithelium (RPE), the transocular d.c. potential decreased; the azide response became smaller and then was inverted in polarity, whereas the SCN- response became larger. Azide and SCN- are assumed to depolarize and hyperpolarize the basal membrane of RPE, respectively. The equilibrium potential of ions passing through the putative azide-sensitive channels is assumed less negative than resting potential of RPE cells. The SCN- response probably represents a diffusion potential of SCN- permeating through anionic channels at a higher rate than Cl-. Results demonstrate the feasibility of in vivo electrophysiological measurement of the functional state and the structural integrity of RPE under pathological conditions.

Animals↗

PubMed1997

Further studies on the inactivation by sodium azide of lignin peroxidase from Phanerochaete chrysosporium.

Azide ion is a mechanism-based inactivator of horseradish peroxidase [Ortiz de Montellano et al. (1988) Biochemistry 27, 5470-5476] and the peroxidase from the coprophilic fungus Coprinus macrorhizus [DePillis and Ortiz de Montellano (1989) Biochemistry 28, 7947-7952]. These peroxidases mediate the one-electron oxidation of azide ion-forming azidyl radical. Inactivation of these enzymes is caused by covalent modification of the heme prosthetic groups by azidyl radical. Lignin peroxidases from the wood-rotting fungus Phanerochaete chrysosporium are also inactivated when they catalyze oxidation of azide ion [Tuisel et al. (1991) Arch. Biochem. Biophys. 288, 456-462; DePillis et al. (1990) Arch. Biochem. Biophys. 280, 217-223]. Following inactivation of horseradish peroxidase and the peroxidase from C. macrorhizus substantial amounts of azidyl-heme adducts have been found. Only trace amounts of such adducts have been found following azide-mediated inactivation of lignin peroxidase. Nevertheless, we have shown that during oxidation of azide by lignin peroxidase H8 destruction of heme occurred and a substantial fraction of the enzyme is irreversibly inactivated. However, the rest of the enzyme forms a relatively stable ferrous-nitric oxide (NO) complex. Although this complex appears to be an inactivated form of the enzyme, we have shown that, when present as the ferrous-NO complex, the enzyme is actually protected from inactivation. The lignin peroxidase ferrous-NO complex reverts slowly (t1/2 = 6.3 x 10(3) s) to the ferric form. Reversion is accelerated if the complex is chromatographed on a PD-10 (Sephadex G-25) column or if veratryl alcohol is added. If azide and hydrogen peroxide (a required cosubstrate) are present (or added), the enzyme undergoes another cycle of catalysis and further inactivation. A detailed reaction mechanism is proposed that is consistent with our experimental observations, the chemistry of azide, and our current understanding of peroxidases.

Azides↗

PubMed1993

Phenyl-azide-mediated photocrosslinking analysis of Cro-DNA interaction.

Using phenyl-azide-mediated photocrosslinking, we show that the alpha carbon of amino acid 2 of the helix-turn-helix motif of bacteriophage lambda Cro is within 12 A of the bottom-strand nucleotides at positions 2 and 3 of the DNA half site in the Cro-DNA complex in solution. This result is in excellent agreement with the crystallographic structure of the Cro-DNA complex. The results of phenyl-azide-mediated photocrosslinking analysis of Cro-DNA interaction, together with the previously reported results of phenyl-azide-mediated photocrosslinking analysis of CAP-DNA interaction, establish that phenyl-azide-mediated photocrosslinking is generalizable and provide information regarding the structural requirements for phenyl-azide-mediated photocrosslinking. Comparison of the results of phenyl-azide-mediated photocrosslinking to the results of EDTA: iron-mediated affinity cleaving indicates that phenyl-azide-mediated photocrosslinking yields superior resolution.

Azides↗

PubMed1987

The distance between cytochromes a and a3 in the azide compound of bovine-heart cytochrome oxidase.

The electron-spin relaxation rates of the two species of cytochrome a3(3+)-azide found in the azide compound of bovine-heart cytochrome oxidase were measured by progressive microwave saturation at T = 10 K. It has been shown previously that Cyt a3(3+)-azide gives rise to two distinct EPR resonances, depending upon the oxidation state of Cyt a. When Cyt a is ferrous, Cyt a3(3+)-azide has g = 2.88, 2.19 and 1.64; upon oxidation of Cyt a, the a3(3+)-azide g-values become g = 2.77, 2.18, and 1.74 (Goodman, G. (1984) J Biol. Chem. 259, 15094-15099). The relaxation effect of Cyt a on Cyt a3 could be measured as the difference in microwave field saturation parameter H1/2 between the g = 2.77 and g = 2.88 species. For each signal the spin-lattice relaxation time T1 was determined from H1/2 using the transverse relaxation time T2. The value of T2 at 10 K was extrapolated from a plot of line-width vs. temperature at higher temperature. The dipolar contribution to T1 was related to the Cyt a-Cyt a3 spin-spin distance utilizing available information on the relative orientation of Cyt a3-azide and Cyt a (Erecińska, M., Wilson, D.F. and Blasie, J.K. (1979) Biochim. Biophys. Acta 545, 352-364). By taking into account the relaxation parameters for both gx and gz components of the Cyt a3-azide g-tensor, the angle between the gz components of the Cyt a and Cyt a3 g-tensors was determined to be between 0 and 18 degrees, and the Cyt a-Cyt a3 spin-spin distance was found to be 19 +/- 8 A.

Anaerobiosis↗

PubMed1976

Interference of sodium azide with the quantitation of serum cholesterol: a comparative study.

Interference of sodium azide (employed widely as a preservative for serum) with six different cholesterol methods and two modified procedures is analyzed and compared. Sodium azide is shown to lower the serum cholesterol values of the iron-cholesterol methods from 5 to 50% at 0.1 g% azide, and from 60 to 95% at 1.0 g% azide concentration, depending on the method employed. This inhibition is independent of serum cholesterol concentration. Increased serum to reagent (v/v) ratio, i.e., increased azide concentration, caused increased depression of serum cholesterol values. Appropriate choice of low serum-to-reagent (v/v) ratio thus decreases the magnitude of the azide interference in the iron-cholesterol reaction to 3-10% for the precipitation procedures, and to 25% for the non-precipitation procedure at 0.1 g% azide concentration in serum.

Azides↗

PubMed1981

Effect of sodium azide on sister-chromatid exchanges in human lymphocytes and Chinese hamster cells.

Previous reports from this laboratory and others indicate that sodium azide is a unique mutagen. It is highly mutagenic in S. typhimurium TA1530 as well as in barley, rice, peas, yeast and Chinese hamster V79 cells. However, azide apparently does not produce chromosome breaks in barley, Vicia or human lymphocytes. Therefore, a study of the effects of azide on sister-chromatid exchanges (SCE) appeared warranted. Human whole blood and Chinese hamster K1 cell line were exposed for 4 and 2 h resp. to various concentrations of sodium azide ranging from 10(-3) to 10(-7) M. Cells were harvested and chromosomes stained by the FPG technique. In human lymphocytes, concentrations above 10(-4) induced lethality whereas the K1 cell line was sensitive to concentrations above 10(-5) M. The lower concentrations of azide produced no significant increase in SCE frequency above controls. Concurrent mitomycin C treatments produced significant increases in SCE levels. This apparent lack of induction of SCEs above background combined with previous data demonstrating negative clastogenic but very positive mutagenic activity of azide confirms the uniqueness of this mutagen. It would appear that azide is one of the few known potent mutagens that does not increase SCEs and/or break chromosomes.

Animals↗

PubMed1983

A mutagenic metabolite synthesized by Salmonella typhimurium grown in the presence of azide is azidoalanine.

A mutagenic azide metabolite was purified from the medium in which Salmonella typhimurium cells were grown in the presence of azide. This metabolite was identified to be azidoalanine based on infrared and mass spectroscopy and elemental analysis. This compound appeared to be identical to the mutagenic compound synthesized in vitro from azide and O-acetylserine by partially purified O-acetylserine sulfhydrylase. The metabolite (azidoalanine) mutagenic efficiency and spectrum in S. typhimurium was similar to that of inorganic azide. The compounds 2-azidoethylamine, 2-bromoethylamine, 3-bromopropionic acid and N-(azidomethyl) phthalimide were also mutagenic with a similar spectrum to azide and azidoalanine, but with lower efficiency. The compounds 3-azidopropylamine, 4-azidobutylamine, 3-chloroalanine and ethylamine were only weakly or nonmutagenic. Numerous other chloro, bromo and azido phthalimide derivatives tested were nonmutagenic. It is suggested that the lack of azide mutagenicity (and perhaps carcinogenicity) in mammalian cells may be due to their inability to convert azide to azidoalanine.

Alanine↗