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PubMed1991

NTP Toxicology and Carcinogeneis Studies of Sodium Azide (CAS: 26628-22-8) in F344 Rats (Gavage Studies).

Sodium azide is a white crystalline solid used in the manufacture of the explosive lead azide. It is the principal chemical used to generate nitrogen gas in automobile safety airbags and airplane escape chutes and is a broad-spectrum biocide used in both research and agriculture. Toxicology and carcinogenicity studies were conducted by administering sodium azide (greater than 99% pure) in distilled water by gavage to groups of male and female F344/N rats once daily, 5 days per week for 14 days, 13 weeks, or 2 years. Genetic toxicology studies were conducted in Salmonella typhimurium and Chinese hamster ovary cells. 14-Day Studies: Rats received 0, 5, 10, 20, 40, or 80 mg/kg sodium azide. All male and female rats receiving 40 or 80 mg/kg and two of five female rats receiving 20 mg/kg died during the first week of the studies. Clinical findings of toxicity included lethargy and inactivity. No grossly observable lesions were present in any of the dose groups. 13-Week Studies: Rats received 0, 1.25, 2.5, 5, 10, or 20 mg/kg sodium azide. Seven of 9 males and all 10 females receiving 20 mg/kg died before the end of the studies. Final mean body weights of treated rats were within 10% of those of the controls. Compound-related clinical findings of toxicity in the 20 mg/kg dose groups included lethargy and labored breathing. Histopathologic lesions induced by sodium azide were limited to the brain (necrosis of the cerebrum and thalamus) and lung (congestion, hemorrhage, and edema), and were observed in rats receiving 20 mg/kg that died during the studies. Body Weights, Feed Consumption, and Survival in the 2-Year Studies: Because compound-related deaths were observed in the groups receiving 20 mg/kg in the 13-week studies, lower dose levels were used in the 2-year studies. Two-year studies were conducted by administering 0, 5, or 10 mg/kg sodium azide to groups of 60 male and 60 female rats. Dose-related depression in mean body weight was observed throughout the study period. Mean feed consumption values in low- and high-dose groups were lower than control values. Survival of high-dose rats of each sex was significantly (P<0.05) lower than controls (males-control, 24/60; low-dose, 27/60; high-dose, 9/60; females-37/60; 43/60; 21/59). The reduced survival was attributed to brain necrosis and cardiovascular collapse induced by sodium azide. Neoplastic and Nonneoplastic Effects in the 2-Year Studies: There were no compound-related increases in incidences of neoplasms in rats. Significantly decreased incidences were observed for certain neoplasms, including mononuclear cell leukemia in male rats (control, 33/60; low-dose, 28/60; high-dose, 14/60), adrenal gland pheochromocytoma in male rats (26/55; 16/56; 6/54), mammary gland fibroadenoma in female rats (20/60; 11/60; 8/59), and pituitary gland neoplasms in female rats (37/60; 28/60; 17/59). These decreases reflected to some extent, but could not be attributed solely to, the reduced survival of the high-dose groups. Compound-related nonneoplastic brain lesions (necrosis of the cerebrum and thalamus) were observed at significantly (P<0.001) increased incidences in high-dose male and female rats. The increased incidence of lung congestion observed in this dose group was considered due to cardiovascular collapse secondary to brain necrosis. Genetic Toxicology: Sodium azide was mutagenic in Salmonella typhimurium strains TA100 and TA1535, with or without exogenous metabolic activation (S9); it was not mutagenic in strain TA1537 or TA98. In cytogenetic tests with Chinese hamster ovary cells, sodium azide induced sister chromatid exchanges, but not chromosomal aberrations, in the presence and the absence of S9. Conclusions: Under the conditions of these 2-year gavage studies, there was no evidence of carcinogenic activity of sodium azide in male or female F344/N rats administered 5 or 10 mg/kg. Sodium azide induced necrosis in the cerebrum and the thalamus of the brain in both male and female rats. Synonyms: Azide, Azium, Smite

Journal Article↗
PubMed2000

Direct interaction of Na-azide with the KATP channel.

1. The effects of the metabolic inhibitor sodium azide were tested on excised macropatches from Xenopus oocytes expressing cloned ATP-sensitive potassium (KATP) channels of the Kir6.2/SUR1 type. 2. In inside-out patches from oocytes expressing Kir6.2 delta C36 (a truncated form of Kir6.2 that expresses in the absence of SUR), intracellular Na-azide inhibited macroscopic currents with an IC50 of 11 mM. The inhibitory effect of Na-azide was mimicked by the same concentration of NaCl, but not by sucrose. 3. Na-azide and NaCl blocked Kir6.2/SUR1 currents with IC50 of 36 mM and 19 mM, respectively. Inhibition was abolished in the absence of intracellular Mg2+. In contrast, Kir6.2 delta C36 currents were inhibited by Na-azide both in the presence or absence of intracellular Mg2+. 4. Kir6.2/SUR1 currents were less sensitive to 3 mM Na-azide in the presence of MgATP. This apparent reduction in sensitivity is caused by a small activatory effect of Na-azide conferred by SUR. 5. We conclude that, in addition to its well-established inhibitory effect on cellular metabolism, which leads to activation of KATP channels in intact cells, intracellular Na-azide has direct effects on the KATP channel. Inhibition is intrinsic to Kir6.2, is mediated by Na+, and is modulated by SUR. There is also a small, ATP-dependent, stimulatory effect of Na-azide mediated by the SUR subunit. The direct effects of 3 mM Na-azide on KATP channels are negligible in comparison to the metabolic activation produced by the same Na-azide concentration.

Adenosine Triphosphate↗
PubMed2006

Comparative first-principles study of structural and optical properties of alkali metal azides.

A comparative first-principles study of the structural and optical properties of the alkali metal azides has been performed with density functional theory within the generalized gradient approximation. The crystal structures of the alkali azides compare well with experimental data. Their ionic character is manifested by the closeness of their internitrogen distances to the calculated N-N bond length for the free azide ion. An analysis of electronic structure, charge transfer, and bond order shows that the alkali azides are all wide-gap insulators and ionic compounds. The energy band and density of states for lithium azide and alpha-sodium azide are very similar, while these for potassium azide, alpha-rubidium azide, and alpha-cesium azide are alike, but some modifications are observed with the increment of alkali metals' electropositivity. These changes are closely related to the differences of the crystal structures. The general shapes of the real and imaginary parts of the dielectric function, adsorption coefficient, and electron energy-loss spectra are quite similar. The peaks originate from the electron transitions from the alkali metal s and p states to the conduction band. Our calculated optical properties for the alkali azides are found to be in good agreement with available experimental data. The absorption spectra of the alkali azides show a number of absorption peaks, which are believed to be associated with different exciton states, in the fundamental absorption region. In general, the electron energy-loss spectra have two plasma frequencies.

Journal Article↗
PubMed1996

Exposures and health effects: an evaluation of workers at a sodium azide production plant.

Sodium azide is the principal gas-generating agent used to inflate automobile supplemental restraint systems, more commonly called airbags. Although sodium azide is known to affect the cardiovascular system by causing peripheral vasodilation, there is no published literature describing occupational exposures to sodium azide in the rapidly growing automobile airbag industry. In 1994-1995, the National Institute for Occupational Safety and Health (NIOSH) conducted a cross-sectional study of health complaints reported by sodium azide production workers at the only continuous sodium azide production facility in the United States. The NIOSH evaluation consisted of a plant industrial hygiene survey, a symptom questionnaire, ambulatory blood pressure monitoring, and blood azide analysis. Personal breathing zone air monitoring revealed exposures to sodium azide and hydrazoic acid (a reactant product) at levels greater than the NIOSH Recommended Exposure Limits (RELs). In some cases, exposures exceeded the REL despite the use of air-supplied respirators. The questionnaire revealed that most workers reported headache (10 of 11 [91%]), episodes of low blood pressure (9 of 11 [82%]), and palpitations (8 of 11 [73%]) occurring in the production areas within the 6 months preceding the study. Mild headache (4 of 11 [36%]) was the only symptom reported during our 24-hr medical survey. Ambulatory blood pressure monitoring revealed one asymptomatic employee with a drop in blood pressure (defined as a drop in systolic [at least 20 mm Hg] and diastolic [at least 10 mm Hg] blood pressure) during a period of exposure to sodium azide at a level five times the NIOSH REL. Improvements in plant engineering controls, increased attention to employee hygiene practices, and a more comprehensive respiratory protection program were recommendations made by NIOSH to reduce exposures at the plant. All facilities handling sodium azide should be aware of the potential toxicity of sodium azide and hydrazoic acid.

Adult↗
PubMed1983

Lack of induction of single-strand breaks in mammalian cells by sodium azide and its proximal mutagen.

The mutagenicity of sodium azide in both higher plants and bacteria is well documented. However, in mammalian cells, research on the effects of azide on gene mutations has produced conflicting results. Furthermore, no research has been conducted on the effects of azide and its proximal mutagen (mutagenic metabolite) on DNA single-strand breaks. Experiments were designed to overcome this lack of information on azide mutagenicity and to evaluate the potential hazard of azide exposure to man. Chinese hamster V79 cells were treated with either azide or its proximal mutagen(s) for 2 or 6 h, respectively, and analyzed by alkaline elution for single-strand breaks. The data showed that neither azide nor the proximal mutagen(s) induced single-strand DNA breaks or DNA-protein cross-links. Therefore it appears that neither azide nor its proximal mutagen(s) interact directly with DNA and this suggests that azide may be an indirect-acting mutagen. Furthermore, this lack of interaction with DNA may account for azide's lack of carcinogenicity.

Animals↗
PubMed1989

Azide as a probe of co-operative interactions in the mitochondrial F1-ATPase.

(1) The hydrolytic activity of the isolated mitochondrial ATPase (F1) is strongly inhibited by azide. However, at very low ATP concentration (1 microM or less), no inhibition by azide is observed. (2) The azide-insensitive ATPase activity represents a high-affinity, low-capacity mode of turnover of F1. This is identified with the low Km, low Vmax component seen in steady-state kinetic studies in the absence of azide. (3) The azide-insensitive ATPase activity shows simple Michaelis-Menten kinetics, with Km = 3.2 microM, and Vmax = 1.1 mumol/min per mg (6 s-1). It is unaffected by anions such as sulphite, or by increasing pH in the range 7 to 8, both of which stimulate the maximal activity of F1. (4) Both the azide-insensitive and azide-sensitive components of F1-ATPase activity are equally inhibited by labelling the enzyme with 7-chloro-4-nitrobenzofurazan, by binding the natural inhibitor protein, or by cold denaturation of the enzyme. (5) It is concluded that azide-insensitive ATP hydrolysis represents catalysis by F1 involving a single catalytic site, and that azide acts by abolishing intersubunit cooperativity between the three catalytic sites of F1. Azide-sensitivity is thus a useful probe for events which affect the active site of F1 directly.

Adenosine Triphosphate↗
PubMed1999

Inhibition of an ecto-ATP-diphosphohydrolase by azide.

Cell surface ATPases (ecto-ATPases or E-ATPases) hydrolyze extracellular ATP and other nucleotides. Regulation of extracellular nucleotide concentration is one of their major proposed functions. Based on enzymatic characterization, the E-ATPases have been divided into two subfamilies, ecto-ATPases and ecto-ATP-diphosphohydrolases (ecto-ATPDases). In the presence of either Mg2+ or Ca2+, ecto-ATPDases, including proteins closely related to CD39, hydrolyze nucleoside diphosphates in addition to nucleoside triphosphates and are inhibited by millimolar concentrations of azide, whereas ecto-ATPases appear to lack these two properties. This report presents the first systematic kinetic study of a purified ecto-ATPDase, the chicken oviduct ecto-ATPDase (Strobel, R.S., Nagy, A.K., Knowles, A.F., Buegel, J. & Rosenberg, M.O. (1996) J. Biol. Chem. 271, 16323-16331), with respect to ATP and ADP, and azide inhibition. Km values for ATP obtained at pH 6.4 and 7.4 are 10-30 times lower than for ADP and the catalytic efficiency is greater with ATP as the substrate. The enzyme also exhibits complicated behavior toward azide. Variable inhibition by azide is observed depending on nucleotide substrate, divalent ion, and pH. Nearly complete inhibition by 5 mm azide is obtained when MgADP is the substrate and when assays are conducted at pH 6-6.4. Azide inhibition diminishes when ATP is the substrate, Ca2+ as the activating ion, and at higher pH. The greater efficacy of azide in inhibiting ADP hydrolysis compared to ATP hydrolysis may be related to the different modes of inhibition with the two nucleotide substrates. While azide decreases both Vmax and Km for ADP, it does not alter the Km for ATP. These results suggest that the apparent affinity of azide for the E.ADP complex is significantly greater than that for the free enzyme or E.ATP. The response of the enzyme to three other inhibitors, fluoride, vanadate, and pyrophosphate, is also dependent on substrate and pH. Taken together, these results are indicative of a discrimination between ADP and ATP by the enzyme. A mechanism of azide inhibition is proposed.

Adenosine Diphosphate↗
PubMed1999

Azide binding to the trinuclear copper center in laccase and ascorbate oxidase.

Azide binding to the blue copper oxidases laccase and ascorbate oxidase (AO) was investigated by electron paramagnetic resonance (EPR) and pulsed electron-nuclear double resonance (ENDOR) spectroscopies. As the laccase : azide molar ratio decreases from 1:1 to 1:7, the intensity of the type 2 (T2) Cu(II) EPR signal decreases and a signal at g approximately 1.9 appears. Temperature and microwave power dependent EPR measurements showed that this signal has a relatively short relaxation time and is therefore observed only below 40 K. A g approximately 1.97 signal, with similar saturation characteristics was found in the AO : azide (1:7) sample. The g < 2 signals in both proteins are assigned to an S = 1 dipolar coupled Cu(II) pair whereby the azide binding disrupts the anti-ferromagnetic coupling of the type 3 (T3) Cu(II) pair. Analysis of the position of the g < 2 signals suggests that the distance between the dipolar coupled Cu(II) pair is shorter in laccase than in AO. The proximity of T2 Cu(II) to the S = 1 Cu(II) pair enhances its relaxation rate, reducing its signal intensity relative to that of native protein. The disruption of the T3 anti-ferromagnetic coupling occurs only in part of the protein molecules, and in the remaining part a different azide binding mode is observed. The 130 K EPR spectra of AO and laccase with azide (1:7) exhibit, in addition to an unperturbed T2 Cu(II) signal, new features in the g parallel region that are attributed to a perturbed T2 in protein molecules where the anti-ferromagnetic coupling of T3 has not been disrupted. While these features are also apparent in the AO : azide sample at 10 K, they are absent in the EPR spectra of the laccase : azide sample measured in the range of 6-90 K. Moreover, pulsed ENDOR measurements carried out at 4.2 K on the latter exhibited only a reduction in the intensity of the 20 MHz peak of the 14N histidine coordinated to the T2 Cu(II) but did not resolve any significant changes that could indicate azide binding to this ion. The lack of T2 Cu(II) signal perturbation below 90 K in laccase may be due to temperature dependence of the coupling within the trinuclear : azide complex.

Ascorbate Oxidase↗
PubMed1997

A new caged Ca2+, azid-1, is far more photosensitive than nitrobenzyl-based chelators.

BACKGROUND: Photolabile chelators that release Ca2+ upon illumination have been used extensively to dissect the role of this important second messenger in cellular processes such as muscle contraction and synaptic transmission. The caged calcium chelators that are presently available are often limited by their inadequate changes in Ca2+ affinity, selectivity for Ca2+ over Mg2+ and sensitivity to light. As these chelators are all based on nitrobenzyl photochemistry, we explored the use of other photosensitive moieties to generate a new caged calcium with improved properties. RESULTS: Azid-1 is a novel caged calcium in which a fluorescent Ca2+ indicator, fura-2, has been modified with an azide substituent on the benzofuran 3-position. Azid-1 binds Ca2+ with a dissociation constant (Kd) of approximately 230 nM, which changes to 120 microM after photolysis with ultraviolet light (330-380 nm). Mg2+ binding is weak (8-9 mM Kd) before or after photolysis. Azid-1 photolyzes with unit quantum efficiency, making it 40-170-fold more sensitive to light than caged calciums used previously. The photolysis of azid-1 probably releases N2 to form a nitrenium ion that adds water to yield an amidoxime cation; the electron-withdrawing ability of the amidoxime cation reduces the chelator's Ca2+ affinity within at most 2 ms following a light flash. The ability of azid-1 to function as a caged calcium in living cells was demonstrated in cerebellar Purkinje cells, in which Ca2+ photolytically released from azid-1 could replace the normal depolarization-induced Ca2+ transient in triggering synaptic plasticity. CONCLUSIONS: Azid-1 promises to be a useful tool for generating highly controlled spatial and temporal increases of Ca2+ in studies of the many Ca2+-dependent biological processes. Unlike other caged calciums, azid-1 has a substantial cross section or shows a high susceptibility for two-photon photolysis, the only technique that confines the photochemistry to a focal spot that is localized in three dimensions. Azide photolysis could be a useful and more photosensitive alternative to nitrobenzyl photochemistry.

Animals↗
PubMed2000

Effects of azide on the S(2) state EPR signals from Photosystem II.

The anion azide, N(3) (-), has been previously found to be an inhibitor of oxygen evolution by Photosystem II (PS II) of higher plants. With respect to chloride activation, azide acts primarily as a competitive inhibitor but uncompetitive inhibition also occurs [Haddy A, Hatchell JA, Kimel RA and Thomas R (1999) Biochemistry 38: 6104-6110]. In this study, the effects of azide on PS II-enriched thylakoid membranes were characterized by electron paramagnetic resonance (EPR) spectroscopy. Azide showed two distinguishable effects on the S(2) state EPR signals. In the presence of chloride, which prevented competitive binding, azide suppressed the formation of the multiline and g = 4.1 signals concurrently, indicating that the normal S(2) state was not reached. Signal suppression showed an azide concentration dependence that correlated with the fraction of PS II centers calculated to bind azide at the uncompetitive site, based on the previously determined inhibition constant. No evidence was found for an effect of azide on the Fe(II)Q(A) (-) signals at the concentrations used. This result is consistent with placement of the uncompetitive site on the donor side of PS II as suggested in the previous study. In chloride-depleted PS II-enriched membranes azide and fluoride showed similar effects on the S(2) state EPR signals, including a notable increase and narrowing of the g = 4.1 signal. Comparable effects of other anions have been described previously and apparently take place through the chloride-competitive site. The two azide binding sites described here correlate with the results of other studies of Lewis base inhibitors.

Journal Article↗
PubMed1994

Systemic or local administration of azide produces striatal lesions by an energy impairment-induced excitotoxic mechanism.

Sodium azide is an inhibitor of cytochrome oxidase which produces selective striatal lesions in both rodents and primates. In the present study we investigated the neurochemical and histologic effects of both intrastriatal and systemic administration of sodium azide, as well as the age dependence and mechanism of the lesions. Intrastriatal administration of sodium azide produced dose-dependent lesions. Neurochemical and histologic evaluation showed that markers of both spiny projection neurons (GABA, substance P) and aspiny interneurons (somatostatin, neuropeptide Y, NADPH-diaphorase) were equally affected. Subacute systemic administration of sodium azide resulted in lesions with a similar neurochemical profile; however, in contrast to intrastriatal injections there was sparing of dopaminergic striatal afferents. Prior decortication significantly attenuated lesions produced by intrastriatal administration of sodium azide, consistent with an excitotoxic process. Chronic administration of sodium azide for 1 month lead to striatal neuropathological changes. Lesions produced by intrastriatal administration of sodium azide in 1-, 4-, and 12-month-old animals showed age dependence. Both freeze-clamp measurements and chemical-shift magnetic resonance spectroscopy confirmed that sodium azide impairs oxidative phosphorylation in the striatum following either intrastriatal or systemic administration. These results show that the striatum is particularly vulnerable to oxidative stress produced by sodium azide, and that it produces striatal lesions by a secondary excitotoxic mechanism.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1982

Kinetic mechanism of mitochondrial adenosine triphosphatase. Inhibition by azide and activation by sulphite.

1. The initial rapid phase of ATP hydrolysis by bovine heart submitochondrial particles or by soluble F1-ATPase is insensitive to anion activation (sulphite) or inhibition (azide). 2. The second slow phase of ATP hydrolysis is hyperbolically inhibited by azide (Ki approximately 10(-5) M); the inosine triphosphatase activity of submitochondrial particles or F1-ATPase is insensitive to azide or sulphite. 3. The rate of interconversion between rapid azide-insensitive and slow azide-sensitive phases of ATP hydrolysis does not depend on azide concentration, but strongly depends on ATP concentration. 4. Sulphite prevents the interconversion of the rapid initial phase of the reaction into the slower second phase, and also prevents and slowly reverses the inhibition by azide. 5. The presence of sulphite in the mixture when ADP reacts with ATPase of submitochondrial particles changes the pattern of the following activation process. 6. Azide blocks the activation of ATP-inhibited ATPase of submitochondrial particles by phosphoenolpyruvate and pyruvate kinase. 7. The results obtained suggest that the inhibiting effect of azide on mitochondrial ATPase is due to stabilization of inactive E*.ADP complex formed during ATP hydrolysis; the activation of ATPase by sulphite is also realized through the equilibrium between intermediate active E.ADP complex and inactive E*.ADP complex.

Adenosine Diphosphate↗
PubMed1984

Peripheral and central actions of sodium azide on circulatory and respiratory homeostasis in anesthesized cats.

In pentobarbital-anesthesized cats, bolus i.v. injections of sodium azide produced dose-dependent transient hypotension accompanied by a modest tachycardia and a brief hyperpnea. Intracerebroventricular injections of azide elicited graded effects similar to the i.v. doses, but the responses were slower in onset and could be delayed by occluding the cranial blood supply. This is interpreted to mean that intracerebroventricular azide acts systematically after escaping from the cerebrospinal fluid into the bloodstream. The hypotensive response to i.v. azide was not affected by cholinergic or adrenergic blockade or buffer nerve section. The tachycardia was blocked by sympathetic neural blockade or buffer nerve section indicating that it is a baroreflex response to the vasodepressor effect. Respiratory effects of bolus i.v. azide occurred independently of the hypotensive response and were abolished by peripheral chemodenervation. Infusion of azide facilitated CO2-tidal volume responsiveness in the steady state, an effect that was essentially eliminated by carotid sinus neurotomy. The azide did not affect the tidal volume-respiratory frequency relationship mediated by the pulmonary stretch receptors. Thus, the respiratory stimulant effect of azide in subtoxic doses is attributable to an excitatory action on the arterial chemoreceptors. Toxic doses of azide resulted in centrally mediated hypertension, tachycardia, cardiac arrhythmia, respiratory depression, seizures and death.

Animals↗
PubMed1989

A defective proton pump, point-mutated bacteriorhodopsin Asp96----Asn is fully reactivated by azide.

Addition of azide fully restored the proton pump activity of defective bacteriorhodopsin (BR) mutant protein Asp96----Asn. The decay time of M of BR Asp96----Asn, the longest living intermediate, was decreased from 500 ms at pH 7.0 to approximately 1 ms under conditions of saturating azide concentrations. This decay was faster than the decay of M in the wild-type, where no such azide effect was detectable. Stationary photocurrents, measured with purple membranes immobilized and oriented in a polyacrylamide gel, increased upon addition of azide up to the level of the wild-type. Different small anions of weak acids restored the pump activity with decreasing affinity in the order: cyanate greater than azide greater than nitrite greater than formiate greater than acetate. The activation energy of the M decay in the mutant was higher in the presence (48 kJ/mol) than in the absence (27 kJ/mol) of 100 mM azide even though the absolute rate was dramatically increased by azide. This effect of azide is due to the substitution of a carboxamido group for a carboxylic group at position 96 which removes the internal proton donor and causes an increase in the entropy change of activation for proton transfer which is reversed by azide.

Anions↗
PubMed1974

Inhibition of DNA synthesis and cell division in Salmonella typhimurium by azide.

Evidence has been obtained that sodium azide is an inhibitor of cell division in wild-type and aziA strains of Salmonella typhimurium. The bacteria grown in media containing sodium azide and glucose formed long filaments. It has been found that sodium azide had a stronger inhibitory effect on DNA synthesis than on cell mass increase. When filaments produced by azide action were transferred to azide-free medium very rapid increase in DNA content was observed during the first 45 min. After this time, when relative DNA content was increased the rate of DNA synthesis was reduced and cell divisions reappeared. Inhibitory effect of azide on DNA biosynthesis in vitro was observed with toluenized cells of S typhimurium. Only ATP-dependent radioactive dTMP incorporation into DNA was affected by sodium azide. It had no effect on the incorporation in the absence of ATP. Mutant aziC was isolated in S. typhimurium by scoring for clones with normal cell division in the presence of sodium azide. Azide had much less effect on DNA biosynthesis in vivo and in vitro in aziC cells as compared with isogenic controls.

Azides↗
PubMed2005

Stopped-flow Fourier transform infrared spectroscopy allows continuous monitoring of azide reduction, carbon monoxide inhibition, and ATP hydrolysis by nitrogenase.

Stopped-flow FTIR spectroscopy was used to monitor continuously the pre-steady- and steady-state phases of azide reduction by nitrogenase and the accompanying hydrolysis of ATP. This was characterized by a ca. 1.3 s lag phase that is explained by the number of Fe protein cycles required to effect the reductions of azide to N(2) + NH(3), N(2)H(4) + NH(3), or 3NH(3). Extrapolation of the steady-state time course for azide reduction to zero time showed that one azide binds within 200 ms to each FeMo cofactor. Inhibition of azide reduction by CO was established at times <400 ms, which was faster than the appearance of the first observable IR band assigned to CO (1904 cm(-)(1) detectable at ca. 1 s with maximum amplitude at ca. 7 s). IR bands associated with the rapidly formed (<400 ms) CO species that inhibits azide reduction were not observed over the range 1700-2100 cm(-)(1). This suggests either that the CO is initially bridging two or more Fe atoms or that a rapid reduction of CO to a formyl state occurs by insertion into a metal-hydride bond. The frequencies and time courses for the appearance and loss of the CO bands under hi- and lo-CO conditions were essentially unaffected by the presence of 20 mM azide, consistent with CO being a noncompetitive inhibitor of azide reduction and with azide and CO binding to different sites on the FeMo cofactor.

Adenosine Diphosphate↗
PubMed2005

Synthesis of structurally defined scaffolds for bivalent ligand display based on glucuronic acid anilides. The degree of tertiary amide isomerism and folding depends on the configuration of a glycosyl azide.

[structures: see text] Syntheses and structural analyses of bivalent carbohydrates based on anilides of glucuronic acid are described. Secondary anilides predominantly adopted the Z-anti structure; there is also evidence for population of the Z-syn isomer. Bivalent tertiary anilides displayed two signal sets in their NMR spectra, consistent with the presence of (i) a major isomer where both amides have E configurations (EE) and (ii) a minor isomer where one amide is E and the other Z (EZ). Qualitative NOE/ROE spectroscopic studies in solution support the proposal that the anti conformation is preferred for E amides. The crystal structure of one bivalent tertiary anilide showed E-anti and E-syn structural isomers; intramolecular carbohydrate-carbohydrate stacking was observed and mediated by carbonyl-pyranose, azide-azide, and pyranose-aromatic interactions. The EE to EZ isomer ratio, or the degree of folding, for tertiary amides, was greatest for a bivalent compound containing two alpha-glycosyl azide groups; this was enhanced in water, suggesting that hydrophobic interactions are partially but not wholly responsible. Computational methods predicted azide-aromatic (N...H-C interaction) and azide-azide interactions for folded isomers. The close contact of the azide and aromatic protons (N...H-C interaction) was observed upon examination of the close packing in the crystal structure of a related monomer. It is proposed that the alpha-azide group is more optimally aligned, compared to the beta-azide, to facilitate interaction and minimize the surface area of the hydrophobic groups exposed to water, and this leads to the increased folding. The alkylation of bivalent secondary anilides induces a switch from Z to E amide that alters the scaffold orientation. The synthesis of a bivalent mannoside, based on a secondary anilide scaffold, for investigation of mannose-binding receptor cross-linking and lattice formation is described.

Amides↗
PubMed1998

Structural and spectroscopic studies of azide complexes of horse heart myoglobin and the His-64-->Thr variant.

The high-resolution X-ray crystallographic structures of horse heart azidometmyoglobin complexes of the wild-type protein and the His-64-->Thr variant have been determined to 2.0 and 1.8 A respectively. Azide binds to wild-type metmyoglobin in a bent configuration with an Fe-N-1-N-3 angle of 119 degrees and is oriented into the distal crevice in the direction of Ile-107. The proximity of the His-64 NE2 atom to the N-1 atom of the bound azide indicates stabilization of the ligand by the His-64 side chain through hydrogen bonding. In addition, structural characterization of wild-type horse heart azidometmyoglobin establishes that the only structural change induced by ligand binding is a small movement of the Leu-29 side chain away from the azide ligand. EPR and Fourier transform infrared spectroscopy were used to characterize the myoglobin azide complexes further. EPR spectroscopy revealed that, in contrast with wild-type azidometmyoglobin, two slightly different low-spin species are formed by azide bound to the His-64-->Thr variant both in solution and in a polycrystalline sample. One of these low-spin species has a greater relative intensity, with g values very similar to those of the azide complex of the wild-type protein. These EPR results together with structural information on this variant indicate the presence of two distinct conformations of bound azide, with one form predominating. The major conformation is comparable to that formed by wild-type myoglobin in which azide is oriented into the distal crevice. In the minor conformation the azide is oriented towards the exterior of the protein.

Animals↗