Elucidating the binding properties of methemoglobin in red blood cell to cyanide, hydrosulfide, and azide ions using artificial red blood cell

Methemoglobin (metHb), the oxidized form of hemoglobin, lacks the ability of reversible oxygen binding; however, it has a high binding affinity to toxic substances such as cyanide, hydrosulfide, and azide. This innate property of metHb offers the clinical option to treat patients poisoned with these toxins, by oxidizing the endogenous hemoglobin in the red blood cells (RBCs). The binding properties of naked metHb (isolated from RBC) with these toxins has been studied; however, the binding behaviors of metHb under the intracellular conditions of RBC are unclear because of the difficulty in detecting metHb status changes in RBC. This study aimed to elucidate the binding properties of metHb in RBC under physiological and poisoned conditions using artificial RBC, which was hemoglobin encapsulated in a liposome. The mimic-circumstances of metHb in RBC (metHb-V) was prepared by oxidizing the hemoglobin in artificial RBC. Spectroscopic analysis indicated that the metHb in metHb-V exhibited a binding behavior different from that of naked metHb, depending on the toxic substance: When the pH decreased, (i) the cyanide binding affinity of metHb-V remained unchanged, but that of naked metHb decreased (ii) the hydrosulfide binding affinity was increased in metHb-V but was decreased in naked metHb. (iii) Azide binding was increased in metHb-V, which was similar to that in naked metHb, irrespective of the pH change. Thus, the binding behavior of intracellular metHb in the RBC with cyanide, hydrosulfide, and azide under physiological and pathological conditions were partly elucidated using the oxidized artificial RBC.

Systematic identification of the protein substrates of UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferase-T1/T2/T3 using a human proteome microarray

O-GalNAc glycosylation is the initial step of the mucin-type O-glycosylation. In humans, it is catalyzed by a family of 20 homologous UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferases (ppGalNAc-Ts). So far, there is very limited information on their protein substrate specificities. In this study, we developed an on-chip ppGalNAc-Ts assay that could rapidly and systematically identify the protein substrates of each ppGalNAc-T. In detail, we utilized a human proteome microarray as the protein substrates and UDP-GalNAz as the nucleotide sugar donor for click chemistry detection. From a total of 16 368 human proteins, we identified 570 potential substrates of ppGalNAc-T1, T2, and T3. Among them, 128 substrates were overlapped, while the rest were isoform specific. Further cluster analysis of these substrates showed that the substrates of ppGalNAc-T1 had a closer phylogenetic relationship with that of ppGalNAc-T3 compared with ppGalNAc-T2, which was consistent with the topology of the phylogenetic tree of these ppGalNAc-Ts. Taken together, our microarray-based enzymatic assay comprehensively reveals the substrate profile of the ppGalNAc-T1, T2, and T3, which not only provides a plausible explanation for their partial functional redundancy as reported, but clearly implies some specialized roles of each enzyme in different biological processes.

Targeted Ultrasound-Assisted Cancer-Selective Chemical Labeling and Subsequent Cancer Imaging using Click Chemistry

Metabolic sugar labeling followed by the use of reagent-free click chemistry is an established technique for in vitro cell targeting. However, selective metabolic labeling of the target tissues in vivo remains a challenge to overcome, which has prohibited the use of this technique for targeted in vivo applications. Herein, we report the use of targeted ultrasound pulses to induce the release of tetraacetyl N-azidoacetylmannosamine (Ac4 ManAz) from microbubbles (MBs) and its metabolic expression in the cancer area. Ac4 ManAz-loaded MBs showed great stability under physiological conditions, but rapidly collapsed in the presence of tumor-localized ultrasound pulses. The released Ac4 ManAz from MBs was able to label 4T1 tumor cells with azido groups and significantly improved the tumor accumulation of dibenzocyclooctyne (DBCO)-Cy5 by subsequent click chemistry. We demonstrated for the first time that Ac4 ManAz-loaded MBs coupled with the use of targeted ultrasound could be a simple but powerful tool for in vivo cancer-selective labeling and targeted cancer therapies.

Monitoring Astrocytic Proteome Dynamics by Cell Type-Specific Protein Labeling

The ability of the nervous system to undergo long-term plasticity is based on changes in cellular and synaptic proteomes. While many studies have explored dynamic alterations in neuronal proteomes during plasticity, there has been less attention paid to the astrocytic counterpart. Indeed, progress in identifying cell type-specific proteomes is limited owing to technical difficulties. Here, we present a cell type-specific metabolic tagging technique for a mammalian coculture model based on the bioorthogonal amino acid azidonorleucine and the mutated Mus musculus methionyl-tRNA synthetaseL274G enabling azidonorleucine introduction into de novo synthesized proteins. Azidonorleucine incorporation resulted in cell type-specific protein labeling and retained neuronal or astrocytic cell viability. Furthermore, we were able to label astrocytic de novo synthesized proteins and identified both Connexin-43 and 60S ribosomal protein L10a upregulated upon treatment with Brain-derived neurotrophic factor in astrocytes of a neuron-glia coculture. Taken together, we demonstrate the successful dissociation of astrocytic from neuronal proteomes by cell type-specific metabolic labeling offering new possibilities for the analyses of cell type-specific proteome dynamics.

Line shape analysis of two-dimensional infrared spectra

Ultrafast two-dimensional infrared (2D IR) spectroscopy probes femtosecond to picosecond time scale dynamics ranging from solvation to protein motions. The frequency-frequency correlation function (FFCF) is the quantitative measure of the spectral diffusion that reports those dynamics and, within certain approximations, can be extracted directly from 2D IR line shapes. A variety of methods have been developed to extract the FFCF from 2D IR spectra, which, in principle, should give the same FFCF parameters, but the complexity of real experimental systems will affect the results of these analyses differently. Here, we compare five common analysis methods using both simulated and experimental 2D IR spectra to understand the effects of apodization, anharmonicity, phasing errors, and finite signal-to-noise ratios on the results of each of these analyses. Our results show that although all of the methods can, in principle, yield the FFCF under idealized circumstances, under more realistic experimental conditions they behave quite differently, and we find that the centerline slope analysis yields the best compromise between the effects we test and is most robust to the distortions that they cause.

Identification of ATP-binding regions in the RyR1 Ca²⁺ release channel

ATP is an important modulator of gating in type 1 ryanodine receptor (RyR1), also known as a Ca²⁺ release channel in skeletal muscle cells. The activating effect of ATP on this channel is achieved by directly binding to one or more sites on the RyR1 protein. However, the number and location of these sites have yet to be determined. To identify the ATP-binding regions within RyR1 we used 2N₃ATP-2′,3′-Biotin-LC-Hydrazone (BioATP-HDZ), a photo-reactive ATP analog to covalently label the channel. We found that BioATP-HDZ binds RyR1 specifically with an IC₅₀ = 0.6±0.2 mM, comparable with the reported EC50 for activation of RyR1 with ATP. Controlled proteolysis of labeled RyR1 followed by sequence analysis revealed three fragments with apparent molecular masses of 95, 45 and 70 kDa that were crosslinked by BioATP-HDZ and identified as RyR1 sequences. Our analysis identified four glycine-rich consensus motifs that can potentially constitute ATP-binding sites and are located within the N-terminal 95-kDa fragment. These putative nucleotide-binding sequences include amino acids 699–704, 701–706, 1081–1084 and 1195–1200, which are conserved among the three RyR isoforms. Located next to the N-terminal disease hotspot region in RyR1, these sequences may communicate the effects of ATP-binding to channel function by tuning conformational motions within the neighboring cytoplasmic regulatory domains. Two other labeled fragments lack ATP-binding consensus motifs and may form non-canonical ATP-binding sites. Based on domain topology in the 3D structure of RyR1 it is also conceivable that the identified ATP-binding regions, despite their wide separation in the primary sequence, may actually constitute the same non-contiguous ATP-binding pocket within the channel tetramer.

[Evaluation of pathogen disinfection efficacy by chlorine and monochloramine disinfection based on quantitative PCR combined with propidium monoazide (PMA-qPCR)]

A novel detection method of quantitative PCR combined with a DNA intercalating dye propidium monoazide (PMA-qPCR) was developed and then applied to analyze inactivation efficacy of chlorine and monochloramine on E. coli as a representative organism. The results shows that PMA removed 99.94% and 99.99% DNA from non-viable E. coli and Salmonella cells respectively and PMA-qPCR could effectively differentiate viable bacteria from non-viable bacteria; According to the first-order kinetic model, the inactivation coefficients on E. coli obtained by PMA-qPCR were 2.24 L x (mg x min)-1 and 0.0175 L x (mg x min)-1 for chlorine and monochloramine respectively, both of which were lower than those obtained by traditional plating counting method. In order to inactivate 99% of E. coli, the ct values by PMA-qPCR were 0.9 mg L(-1) min and more than 100 mg x L(-1) x min for chlorine and monochloramine while those by plating counting method were only 0.6 mg x L(-1) x min and 20 mg x L(-1) min, respectively; E. coli concentration detected by conventional qPCR kept almost the same when ct value increased, indicating that conventional qPCR was unable to evaluate inactivation efficacy of both chlorine and monochloramine disinfection. In summary, PMA-qPCR shows to be a promising method for evaluating disinfection efficacy by chlorine and monochloramine more accurately.

The electronic absorption spectra of some acyl azides molecular orbital treatment

The electronic absorption spectra of benzoyl azide and its derivatives: p-methyl, p-methoxy, p-chloro and p-nitrobenzoyl azide were investigated in different solvents. The observed spectra differ basically from the electronic spectra of aryl azides or alkyl azides. Four intense pi-pi* transitions were observed in the accessible UV region of the spectrum of each of the studied compounds. The contribution of charge transfer configurations to the observed transitions is rather weak. Shift of band maximum with solvent polarity is minute. On the other hand, band intensity is highly dependent on the solvent used. The observed transitions are delocalized rather than localized ones as in the case with aryl and alkyl azides. The attachment of the CO group to the azide group in acyl azides has a significant effect on the electronic structure of the molecule. The arrangements as well as energies of the molecular orbitals are different in acyl azides from those in aryl azides. The first electronic transition in phenyl azide is at 276 nm, whereas that of bezoyle azide is at 251 nm. Ab initio molecular orbital calculations using both RHF/6-311G* and B3LYP/6-31+G* levels were carried out on the ground states of the studied compounds. The wave functions of the excited states were calculated using the CIS and the AM1-CI procedures.

Azide-selective sensor based on tripodal iron complex for direct azide determination in aqueous samples

A potentiometric azide-selective sensor based on the use of iron(III) hydrotris(3,5-dimethylpyrazolyl)borate acetylacetonate chloride [Tp(Me2)Fe(acac)Cl] as a neutral carrier for an azide-selective electrode is reported. Effect of various plasticizers, viz. o-nitrophenyloctyl ether (o-NPOE), dioctylphthalate (DOP), dibutylphthalate (DBP), and benzylacetate (BA), and an anion excluder, hexadecyltrimethylammonium bromide (HTAB), with [Tp(Me2)Fe(acac)Cl] complex in poly(vinyl chloride) (PVC) were studied. The best performance was obtained with a membrane composition of [Tp(Me2)Fe(acac)Cl]/HTAB/DOP/PVC in a ratio of 5:2:190:100 (w/w). The sensor exhibits significantly enhanced selectivity toward azide ions over the concentration range 6.3 x 10(-7) to 1.0 x 10(-2) M with a lower detection limit of 3.8 x 10(-7) M and a Nernstian slope of 59.4 +/- 1.1 mV decade(-1). Influences of the membrane composition, pH and possible interfering anions were investigated on the response properties of the electrode. Fast and stable response, good reproducibility, long-term stability and applicability over a wide pH range (3.5-9.0) are demonstrated. The sensor has a response time of 14 s and can be used for at least 45 days without any considerable divergence in the potential response. The proposed electrode shows fairly good discrimination of azide from several inorganic and organic anions. It was successfully applied to the direct determination of azide in orange juice, tea extracts and human urine samples.

Vibrational spectra and analysis of acetohydrazide CH3-CO-NH-NH2

The structural stability of acetohydrazide CH(3)-CO-NH-NH(2) was investigated by DFT-B3LYP and ab initio MP2 calculations with 6-311+G** basis set. The C-N rotational barrier in the molecule was calculated to be about 26 kcal/mol that suggested the planar sp(2) nature of the nitrogen atom of the central NH moiety. The N atom of the terminal NH(2) group was predicted to highly prefer the pyramidal sp(3) structure with an inversion barrier of about 7-8 kcal/mol. The molecule was predicted to have a trans-syn (N-H bond is trans with respect to CO bond and NH(2) moiety is syn to C-N bond) conformation as the lowest energy structure. The vibrational frequencies were computed at B3LYP level of theory and normal coordinate calculations were carried out for the trans-syn acetohydrazide. Complete vibrational assignments were made on the basis of normal coordinate analyses and experimental infrared and Raman data.

Spectrophotometric, difference spectroscopic, and high-performance liquid chromatographic methods for the determination of cefixime in pharmaceutical formulations

Three simple and sensitive spectrophotometric, difference spectroscopic, and liquid chromatographic (LC) methods are described for the determination of cefixime. The first method is based on the oxidative coupling reaction of cefixime with 3-methyl-2-benzothiazolinon hydrazone HCI in presence of ferric chloride. The absorbance of reaction product was measured at the maximum absorbance wavelength (wavelength(max)), 630 nm. The difference spectroscopic method is based on the measurement of absorbance of cefixime at the absorbance maximum, 268 nm, and minimum, 237 nm. The measured value was the amplitude of maxima and minima between 2 equimolar solutions of the analyte in different chemical forms, which exhibited different spectral characteristics. The conditions were optimized, and Beer's law was obeyed for cefixime at 1 to 16 microg/mL and 10 to 50 microg/mL, respectively. The third method, high-performance LC, was developed for the determination of cefixime using 50 mM potassium dihydrogen phosphate (pH 3.0)-methanol (78 + 22, v/v) as the mobile phase and measuring the response at wavelength(max) 286 nm. The analysis was performed on a Lichrospher RPC18 column. The calibration curve was obtained for cefixime at 5 to 250 microg/mL, and the mean recovery was 99.71 +/- 0.01%. The methods were validated according to the guidelines of the U.S. Pharmacopoeia and also assessed by applying the standard addition technique. The results obtained in the analysis of dosage forms agreed well with the contents stated on the labels.

A biosensor based on catalase for determination of highly toxic chemical azide in fruit juices

In this work, an amperometric biosensor based on catalase enzyme was developed for the determination of azide. The principle of the measurements was based on the determination of the decrease in the differentiation of oxygen level which had been caused by the inhibition of catalase in the bioactive layer of the biosensor by azide. Firstly, the optimum conditions for the inhibitor biosensor were established. In the optimization studies of the biosensor, the most suitable catalase and gelatin amounts and glutaraldehyde ratio were determined. Optimum catalase activity, optimum gelatin amount and glutaraldehyde percentage were 5000 Ucm(-2), 5.94 mgcm(-2) and 2.5%, respectively. Characterization studies of the biosensor such as optimum pH and optimum temperature were carried out. The repeatability experiments were done and the average value (x), standard deviation (S.D.) and variation coefficient (C.V.) were calculated as 98.6 microM, +/-4.16 microM and 4.23%, respectively. A good linear relationship with a correlation coefficient of 0.9902 was obtained over the concentration range of 25 microM to 300 microM azide. After the optimization and characterization studies the proposed biosensor was applied to the determination of azide in certain fruit juices.

A study of 2-azido-3,5-dichlorobiphenyl by nano- and picosecond laser flash photolysis and computational methods

The dynamics of singlet 3,5-dichloro-2-biphenylnitrene and the products of its rearrangement were monitored by pico- and nanosecond laser flash photolysis and the results were consistent with the predictions of DFT and ab initio molecular orbital calculations.

Presentation and Detection of Azide Functionality in Bacterial Cell Surface Proteins

An improved protocol for copper-catalyzed triazole formation on the bacterial cell surface is described. Addition of highly pure CuBr to cells treated with azidohomoalanine (2) leads to ca. 10-fold more extensive cell surface labeling than previously observed. This highly active catalyst allows detection of the methionine analogues azidoalanine (1), azidonorvaline (3), and azidonorleucine (4) in cell surface proteins. Azidoalanine was previously believed to be silent with regard to the cellular protein synthesis machinery.

Determination of azide as the 3,5-dinitrobenzoyl derivative by capillary electrophoresis

A simple, rapid and reliable capillary electrophoresis method with a photodiode array detector was developed for determination of azide as the 3,5-dinitrobenzoyl derivative in drink samples fortified with sodium azide. Sample preparation was simple and rapid because no more than a simple dilution of samples is needed after quick derivatization. Separation was carried out using a buffer system comprising 25 mM phosphate buffer and 4 mM cetyltrimethylammonium hydroxide at pH 3.0. Methyl benzoate was selected as the internal standard (IS). This study investigated the influence of the concentration of phosphate buffer and electroosmotic flow (EOF) modifier, and the buffer pH on migration time and signal response. The optimized method made it possible to determine azide within 5 min. The limit of detection was determined to be 1.9 microg/ml with SIN > 3. The quantitation range was 6.5-323 microg/ml. By the method recoveries of azide in drink samples fortified with sodium azide were investigated. Mean recovery values ranged from 93.6 to 105.8% and results were satisfactory. In addition, no interference was observed in electropherograms of drink samples fortified with sodium azide. Thus, by this method, azide in drink samples can be determined rapidly with high recoveries and good selectivity despite extremely simple sample preparation.

Trophoblast differentiation in vitro: establishment and characterisation of a serum-free culture model for murine secondary trophoblast giant cells

Differentiation of trophoblast giant cells is an early event during the process of murine embryo implantation. However, differentiation of secondary trophoblast giant cells in the rodent is still only partially understood, probably because of the lack of suitablein vitromodels and cell markers. In order to advance our understanding of trophoblast differentiation, suitablein vitromodels and markers are required to study their development. The objectives of this study were to establish and characterise a serum-freein vitromodel for murine secondary trophoblast cells. Secondary trophoblast giant cells growingin vitroand paraffin sections of day 8.5 postcoitum mouse embryos were processed for immunostaining to establish the expression of potential markers using antibodies to blood group antigens, E-cadherin, α7integrins and activator protein-γ, as well as placental lactogen-II. Within 3 days in serum-free culture, ectoplacental cone-derived secondary trophoblast cells underwent simultaneous induction of both morphological and functional differentiation. Secondary trophoblasts grewin vitroas a monolayer of cells with giant nuclei and expressed B and Le-b/Le-y blood group antigens, α7integrins and placental lactogen-II, as well as activator protein-γ. Transcripts for activator protein-γ and placental lactogen-II were detected in cultures by RT-PCR and for placental lactogen-II byin situhybridisation. At later time-points apoptosis increased. A fibronectin substrate significantly increased secondary trophoblast cell numbers and surface area of outgrowth. The increase in cells with giant nuclei coincided with induction of placental lactogen-II expression. A relationship was found between the nuclear area of secondary trophoblast cells and expression of placental lactogen-II.

Unusual reactions of the model carcinogen N-acetoxy-N-acetyl-2-amino-alpha-carboline

The aqueous solution reactions of the title compound, 1, were examined for comparison to those previously reported for another model carcinogen N-pivaloyloxy-2-amino-alpha-carboline, 2. Both of these are models for the ultimate carcinogenic metabolites of 2-amino-alpha-carboline (AalphaC), a food-derived heterocyclic amine mutagen and carcinogen. The present study was undertaken to determine the effect of the N-acetyl group on the chemistry of such compounds. The N-acetyl group slows down N-O bond cleavage by a factor of (5.5 x 10(3))-fold. This allows other reactions not observed in 2, or in other model carcinogens, to be observed. Among these are acyl-transfer reactions to the aqueous solvent, both uncatalyzed and catalyzed by N3-. In addition, the conjugate acid of 1, 1H+, is subject to a spontaneous decomposition not previously observed in other esters of heterocyclic hydroxylamines or hydroxamic acids. This reaction yields the hydroxylamine, 5, and does so without the intermediacy of the hydroxamic acid, 3, and with 18O exchange from the solvent into the hydroxylamine O. This unique reaction may be caused by an intramolecular proton donation by the pyridyl N-H to the amide carboxyl that catalyzes an intramolecular nucleophilic attack by the carboxyl O of 1H+. A nitrenium ion pathway can still be detected for 1, but, unlike 2 and related esters, this reaction is in competition with other processes throughout the pH range of the study.

Visualization of alpha5 subunit of GABAA/benzodiazepine receptor by 11C Ro15-4513 using positron emission tomography

Although [(11)C]Ro15-4513 and [(11)C]flumazenil both bind to the central benzodiazepine (BZ) receptors, the distributions of the two ligands are not identical in vivo. Moreover, the in vivo pharmacological properties of [(11)C]Ro15-4513 have not been thoroughly examined. In the present study, we examined the pharmacological profile of [(11)C]Ro15-4513 binding in the monkey brain using positron emission tomography (PET). [(11)C]Ro15-4513 showed relatively high accumulation in the anterior cingulate cortex, hippocampus, and insular cortex, with the lowest uptake being observed in the pons. Accumulation in the cerebral cortex was significantly diminished by the BZ antagonist flumazenil (0.1 mg/kg, i.v.), but not that in the pons. Using the pons as a reference region, the specific binding of [(11)C]Ro15-4513 in most of the cerebral cortex including the limbic regions clearly revealed two different affinity sites. On the other hand, specific binding in the occipital cortex and cerebellum showed only a low affinity site. Zolpidem with affinity for alpha1, alpha2, and alpha3 subunits of GABA(A)/BZ receptor fully inhibited [(11)C]Ro15-4513 binding in the occipital cortex and cerebellum, while only about 23% of the binding was blocked in the anterior cingulate cortex. Diazepam with affinity for alpha1, alpha2, alpha3, and alpha5 subunits inhibited the binding in all brain regions. Since Ro15-4513 has relatively high affinity for the alpha5 subunit in vitro, these in vivo bindings of [(11)C]Ro15-4513 can be interpreted as the relatively high accumulation in the fronto-temporal limbic regions representing binding to the GABA(A)/BZ receptor alpha5 subunit.

Cassette mutagenesis and photoaffinity labeling of adenine binding domain of ADP regulatory site within human glutamate dehydrogenase

The adenine binding domain of the ADP site within human glutamate dehydrogenase (GDH) was identified by cassette mutagenesis at the Tyr187 position. The wild type GDH was activated 3-fold by ADP at a concentration of 1 mM at pH 8.0, whereas no significant activation by ADP was observed with the Tyr187 mutant GDH regardless of the size, hydrophobicity, and ionization of the side chains. Studies of the steady-state velocity of the mutant enzymes revealed essentially unchanged apparent K(m) values for 2-oxoglutarate and NADH, but an approximately 4-fold decrease in the respective apparent V(max) values. The binding of ADP to the wild type or mutant GDH was further examined by photoaffinity labeling with [alpha-(32)P]8-azidoadenosine 5'-diphosphate (8N(3)ADP). 8N(3)ADP, without photolysis, mimicked the stimulatory properties of ADP on GDH activity. Saturation of photoinsertion with 8N(3)ADP occurred with apparent K(d) values near 25 microM for the wild type GDH, and the photoinsertion of [alpha-(32)P]8N(3)ADP was decreased best by ADP in comparison to other nucleotides. Unlike the wild type GDH, essentially no photoinsertion was detected for the Tyr187 mutant GDH in the presence or absence of 1 mM ADP. For the wild type GDH, photolabel-containing peptide generated by tryptic digestion was identified in the region containing the sequence EMSWIADTYASTIG, and the photolabeling of this peptide was prevented >95% by the presence of 1 mM ADP during photolysis, whereas no such a peptide was detected for the Tyr187 mutant GDH in the presence or absence of ADP. These results with cassette mutagenesis and photoaffinity labeling demonstrate selectivity of the photoprobe for the ADP binding site and suggest that the photolabeled peptide is within the ADP binding domain of the human GDH and that Tyr187 is responsible for the efficient base binding of ADP to human GDH.

Rapid determination of cyanide and azide in beverages by microdiffusion spectrophotometric method

A rapid screening method was developed for the determination of the toxic volatile anions, cyanide and azide, in beverages. This method consisted of a microdiffusion extraction combined with spectrophotometry using the Konig cyanide reaction and ferric azide complex formation in conjugation with cerium azide oxido-reduction. The time required to achieve full recovery in the extraction of hydrogen cyanide and hydrazoic acid from samples was considerably shortened by increasing the diffusion temperature from 25 degrees C to 40 degrees C. The time required to achieve saturated color development in the Konig cyanide reaction was also shortened by increasing incubation temperature to 40 degrees C. The interference in both azide color reactions was examined for volatile compounds. Cyanide interfered only in the case of ferric azide complex formation. Sulfide, sulfate, nitrite, and acetic acid interfered in both the color reactions. The established method gave a detection limit of 6 microM for cyanide and 0.5mM for azide, and it required only 1 h to determine both anions. Cyanide and azide disappeared by evaporation from beverages during 25 degrees C storage under open conditions in a pH-dependent manner as a function of their respective pKa values of 9.2 and 4.6.

Covalent modification of the catalytic sites of the H+-ATPase from chloroplasts and 2-nitreno-ADP. Modification of the catalytic site 1 (tight) and catalytic sites 1 and 2 together impairs both uni-site and multi-site catalysis of ATP synthesis and ATP hydrolysis

After isolation and purification, the H+-ATPase from chloroplasts, CF0F1, contains one endogenous ADP at a catalytic site, and two endogenous ATP at non-catalytic sites. Incubation with 2-azido-[alpha-32P]ADP leads to tight binding of azidonucleotides. Free nucleotides were removed by three consecutive passages through centrifugation columns, and upon UV-irradiation most of the label was covalently bound. The labelled enzyme was digested by trypsin, the peptides were separated by ion exchange chromatography into nitreno-AMP, nitreno-ADP and nitreno-ATP labelled peptides, and these were then separated by reversed phase chromatography. Amino acid sequence analysis was used to identify the type of the nucleotide binding site. After incubation with 2-azido-[alpha-32P]ADP, the covalently bound label was found exclusively at beta-Tyr-362. Incubation conditions with 2-azido-[alpha-32P]ADP were varied, and conditions were found which allow selective binding of the label to different catalytic sites, designated as 1, 2 and 3 in order of decreasing affinity for ADP, and either catalytic site 1 or catalytic sites 1 and 2 together were labelled. For measurements of the degree of inhibition by covalent modification, CF0F1 was reconstituted into phosphatidylcholine liposomes, and the membranes were energised by an acid-base transition in the presence of a K+/valinomycin diffusion potential. The rate of ATP synthesis was 50-80 s(-1), and the rate of ATP hydrolysis was 15 s(-1) measured under multi-site conditions. Covalent modification of either catalytic site 1 or catalytic sites 1 and 2 together inhibited ATP synthesis and ATP hydrolysis equally, the degree of inhibition being proportional to the degree of modification. Extrapolation to complete inhibition indicates that derivatisation of catalytic site 1 leads to complete inhibition when 1 mol 2-nitreno-ADP is bound per mol CF0F1. Derivatisation of catalytic sites 1 and 2 together extrapolates to complete inhibition when 2 mol 2-nitreno-ADP are bound per CF0F1. The rate of ATP synthesis and the rate of ATP hydrolysis were measured as a function of the substrate concentration from multi-site to uni-site conditions with derivatised CF0F1 and with non-derivatised CF0F1. ATP synthesis and ATP hydrolysis under uni-site and under multi-site condition were inhibited by covalent modification of either catalytic site 1 or catalytic sites 1 and 2 together. The results indicate that derivatisation of site 1 inhibits activation of the enzyme and that cooperative interactions occur at least between the catalytic sites 2 and 3.

Detection of azide in forensic samples by capillary electrophoresis

Azide salts are highly toxic compounds that have been difficult to detect in forensic samples. Here, anion analysis by capillary electrophoresis with indirect spectrophotometric detection was applied to detect azide in forensic specimens from two suicide victims. Gastric specimens from the victims were shown to have high azide concentrations; azide represented one of the major anionic components and no corresponding component occurred in normal gastric juice. Samples of blood and bile had low concentrations of azide near the limits of detection. The method described for azide analysis used simple steps for sample preparation and analysis time was less than 10 min per sample. It offers a simple and reliable method for detecting azide in biological fluids.

Imaging of the super high affinity binding sites for [3H]Ro15-4513 in rat hippocampus: comparison between in vitro and in vivo binding

The super high affinity binding sites for [3H]Ro15-4513, a partial inverse agonist of central benzodiazepine receptors, were analyzed in rat hippocampus both in vivo and in vitro. An ultra high sensitive method of autoradiography with an imaging plate system was employed for quantitative analysis of [3H]Ro15-4513 binding. In in vitro binding, the super high affinity binding sites in the hippocampus were observed when the [3H]Ro15-4513 concentration was below 0.5 nM. In vivo, the super high affinity binding sites were only found when the injected dose of Ro15-4513 was below 3.6 microg/kg and almost disappeared when the dose was increased to 10 microg/kg. These results both in vivo and in vitro indicate that there is a significant discrepancy between actual free ligand concentration in vivo and in vitro, and that concentrations in intact brain may be much lower than previously thought.

Determining sodium azide concentration in blood by ion chromatography

We describe a simple method for measuring sodium azide concentrations in aliquots of blood and other tissues. Aliquots are acidified, converting azide to volatile hydrazoic acid (HN3) which is then trapped in sodium hydroxide. We analyze the resulting aliquots by ion chromatography, using a sodium tetraborate eluent and suppressed conductivity detection. The method is sensitive to at least 100 ng/mL.

Identification of two nucleotide-binding domains on the PB1 subunit of influenza virus RNA polymerase

Influenza virus RNA polymerase is a multifunctional and multisubunit enzyme consisting of three viral P proteins, PB1, PB2, and PA. We have previously shown that radioactive 8-azido GTP (8-N3 GTP) was photo-crosslinked specifically to the PB1 subunit. Here we confirmed the specific crosslinking of PB1 using oxidized GTP and further identified the GTP analogue binding domains after proteolytic cleavage of the crosslinked PB1 with V8 protease. The cleavage pattern of PB1 was determined by analysis of the amino-terminal proximal sequence of fragments generated in the presence of increasing concentrations of V8 protease. The GTP-crosslinking was identified in three fragments: two adjacent fragments, P6 starting from residue 179 and Pllb starting from residue 298; and the third fragment, P11c, starting from residue 458. Thus, we propose that two GTP-binding sites exist in the PB1 subunit, i.e., the amino terminal-proximal site I located at the boundary between P6 and Pllb, and the carboxy terminal proximal site II on P11c fragment. The locations of GTP-binding sites I and II are close to those of sequence motif A and motif D, respectively, conserved among RNA-dependent RNA polymerases. Of the two fragments forming site I, the crosslinking of 8-N3 GTP is higher to P11b, while that of oxidized GTP is higher to P6, suggesting that the ribose and guanine moieties of GTP bound in this binding pocket face P6 and P11c, respectively. From the V8 concentration dependent change in proteolytic cleavage pattern, it is likely that the two GTP-binding sites on PB1 protein are located on structurally different domains. The existence of two GTP-binding sites is discussed in relation to the binding sites for substrates, primers, and products.

Potential of high-performance liquid chromatography with photodiode array detection in forensic toxicology

The potentials and limitations of high-performance liquid chromatography-photodiode array detection are highlighted in respect to its use in the analysis of different biological matrices followed by the identification of unknowns. The logical analytical approach used in clinical and forensic toxicology, vital for the identification of one or more toxic substances as a cause of intoxication, is largely based on both simple and fast "general unknown screening" methods which cover most relevant drugs and potentially hazardous chemicals. In this field of systematic toxicological analysis, a literature overview shows that HPLC can play a substantial role. Both column packing material and eluent composition have their impact on intra- and interlaboratory reproducibility. In view of the sometimes different retention characteristics of various HPLC columns, several possibilities are addressed to enhance the discriminating power of primary retention parameters. The advantages of photodiode array detection as compared to UV detection have been of paramount importance to the success of HPLC in toxicological analysis. Dedicated libraries with spectral information and searching software are powerful tools in the process of identification of an unknown substance. In the present paper, these aspects are also verified in a number of real cases, i.e., trazodone and dothiepin, azide, chloroquine and cocaine, in which we illustrate from our own experience the potentials of HPLC-photodiode array detection in systematic toxicological analysis.

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.

The proteins encoded by the rbs operon of Escherichia coli: I. Overproduction, purification, characterization, and functional analysis of RbsA

The nucleotide-binding component of the high-affinity ribose transport system of Escherichia coli, RbsA, was overproduced from a T7-7 expression vector, and the protein was purified. Biochemical analyses of the purified protein indicated that the ATP analogues, 5'-FSBA and 8-azido ATP, covalently labeled the protein, a reaction that was inhibited by ATP, but not by GTP or CTP. The pure protein exhibited low-level ATPase activity with a K(m) of about 140 microM. Analyses of bacterial strains carrying chromosomal deletions of rbsA and other rbs genes suggested that RbsA is important for the chemotaxis function, a surprising result that was not anticipated from previous studies. However, an inconsistency between the several results from deletion strains raises questions regarding the interpretations of the in vivo data.

Application of high-performance liquid chromatography to a fatality involving azide

We describe a fatality resulting from the ingestion of sodium azide. Initial routine toxicological screening of the blood showed a negative result, but pathological findings as well as findings at the scene itself led to the search for azide. The azide was quantitated in all available postmortem samples (blood, stomach contents, liver, kidney, and bile) and was present in all of these matrices in the following concentrations (micrograms per milliliter or micrograms per gram): 262, 754, 14, 205, and 1283, respectively. The method is based on precolumn derivatization with 3,5-dinitrobenzoyl chloride followed by isocratic high-performance liquid chromatography and photodiode array detection. Methemoglobin and cyanide content in the blood were also elevated.

Photografting of albumin onto dimethyldichlorosilane-coated glass

4-Azido-2-nitrophenyl albumin (ANP-albumin) was prepared by displacing the fluoro group of 4-fluoro-3-nitrophenyl azide (FNPA) by an amino group of albumin. Photolysis of phenyl azides of ANP-albumin was studied by Fourier-transform infrared (FTIR) spectroscopy. The band of phenyl azide disappeared completely after a 12-min exposure to long wave UV light (366 nm), and the photolysis was first-order. Albumin was grafted onto dimethyldichlorosilane-coated glass (DDS-glass) by photolysis of the azido groups of ANP-albumin without any premodification of the surface. The albumin-grafted DDS-glass was characterized by determining the relative amount of nitrogen resulting from the grafted albumin on the surface using electron spectroscopy for chemical analysis (ESCA). The amount of nitrogen increased when the concentration of ANP-albumin in the adsorption solution increased up to 0.1 mg/ml. As the solution concentration increased above this value, the amount of nitrogen decreased. The platelet resistance of the albumin-grafted surfaces was evaluated by measuring the number of adherent platelets and the extent of activation that was quantitated by the area of platelets spread on the surfaces. The maximum platelet-resistant effect was observed when the ANP-albumin was adsorbed for more than 50 min at the solution concentration ranging from 0.05 to 10 mg/ml.

Azide determination in protein samples by ion chromatography

Sodium azide is used as an anti-fungal agent in protein samples in the health related scientific community. Due to its toxic nature, monitoring of the azide level in proteins used in scientific research is necessary. Ion-exchange chromatography has been used to quantitate azide levels in protein samples. Anion-exchange methodology is described which allows for the separation of azide from various common anions found in analytical grade protein sample matrices. The analytical system described utilizes a polymer [poly(styrene-divinylbenzene)] stationary phase which has been surface sulfonated followed by the binding of the aminated latex bead active ion-exchange sites (Dionex, AS4A column). Sodium tetraborate is used as the weak anion-exchange mobile phase. A vendor ion-exchange column comparison is made along with eluent composition and selection studies. Method validation data are presented including: calibration plots for external standardization, limit of detection and method recovery. Various types of proteins are assayed using the described method.

The SOS-Chromo-spottest: evaluation of a short-term test for the determination of genotoxic compounds in contaminated environmental samples

To evaluate the sensitivity of the SOS-Chromo-spottest towards genotoxic compounds 5 reference chemicals (4-nitroquinoline-1-oxide (4-NQO), methylmethansulfonate (MMS), 2,4,7-trinitro-9-fluorenone (TNF), sodium azide (SA) and daunomycin (DM) were tested by 3 different agar plate media (STA-plates: synthetic media containing Xgal, B-plates: synthetic media containing 1% lactose and bromocresolpurple, C-plates: 1% lactose bromocresolpurple media containing complex nutrients). Even 1 ng of 4-NQO showed genotoxic effects by using STA-plates. The threshold value for MMS was 80 nl, for TNF 160 ng and for DM 80 ng. Similarly the spottest with B-plates are positive results, but the sensitivity of this test procedure was 80 to 250 times lower than the STA-plate test. The C-plate test only reacted with high amounts of 4-NQO (1000 ng). Therefore, the SOS-chromo-spottest with STA-media described by Quillardet and Hofnung seems to be a sufficient procedure to detect genotoxic compounds in contaminated environmental samples directly without previous extraction procedures. The simpler B-plates can be used to examine the genotoxicity of certain compounds like industrial or household chemicals where the genotoxicants can be expected to be present in high doses.

The hydroxylation of the salicylate anion by a Fenton reaction and T-radiolysis: a consideration of the respective mechanisms

The yield of 2,3- and 2,5-dihydroxybenzoates (dHB's) from the reaction of .OH radicals with salicylate (SA) ions has been measured as a function of pH and in the presence of oxidants. Under steady-state radiolysis conditions, the production of these products occurs via the reactions .OH + SA----HO-SA. (radical adduct) HO-SA. H+.OH+----2-carboxyphenoxyl radical (SA.) + H2O HO-SA. + SA.----2,3-/2,5-dHB + SA The addition of the oxidants O2, Fe3+ edta, or Fe(CN)63- increases the relative yield of 2,5-dHB/2,3-dHB from about 0.2 to 1. A model to account for this effect is presented. Steady-state radiolyses of 3- and 4-hydroxybenzoate give dihydroxybenzoate products consistent with the phenol group being an ortho-para director in the electrophilic attack of the hydroxyl radical on the aromatic ring. A comparison of product distributions from the reaction of ferrous edta with hydrogen peroxide using salicylate as a scavenger strongly suggests that the same hydroxyl radical adducts are formed as in the radiation experiments.

Inhibited enzyme electrodes. Part 3. A sensor for low levels of H2S and HCN

It is shown that an inhibited enzyme electrode, using cytochrome oxidase, will respond to H2S, HCN and azide ion. For all three inhibitors the kinetics of the inhibiton and recovery processes have been analysed using the theoretical model presented previously (Albery et al., 1990a). Rearrangement of the differential equation describing inhibition and the development of the necessary software has enabled us to obtain values of the concentration of inhibitor in a matter of seconds after exposure of the sensor. The sensor will measure concentrations of H2S down to 1 ppm in the gas phase and concentrations of HCN and azide ion down to 0.4 mumol dm-3 in the solution phase.

Synthesis of spin-labeled 2-azido-ATP: evidence for distinct nucleotide-binding sites in calcium pump protein from sarcoplasmic reticulum

A spin-labeled and photoreactive derivative of ATP was synthesized with the spin label attached to the 2'- or 3'-position of the ribose moiety and an azido group to C2 of the adenine ring (SL-2N3-ATP). Irradiation of this compound at 350 nm generates a nitrene, which then reacts with nucleophiles in its vicinty. SL-2N3-ATP, in the presence of Ca2+, was hydrolyzed by the calcium pump protein (Ca2+-ATPase) of fast twitch skeletal muscle sarcoplasmic reticulum. The SL-2N3-ATP-enzyme complex in the absence of Ca2+ exhibited strongly immobilized ESR spectra. ESR spectra obtained after covalent incorporation of SL-2N3-ATP into Ca2+-ATPase and removal of freely tumbling SL-2N3-ATP exhibited motionally constrained species indicative of distinct and possibly adjacent ATP-binding sites. By contrast, with SL-ATP devoid of the azido group or with the corresponding 'non-cleavable' beta, gamma-methylene triphosphate analogue (SL-AMP-PCP), two distinct sites were not as well resolved in the ESR spectra due to spectral overlap with the signal from the freely tumbling fraction even with the enhanced spectral resolution provided by perdeuteration of the spin label. Thus, SL-2N3-ATP may have general application for ESR studies of ATP-dependent proteins under conditions in which non-covalent interactions are too weak for motionally restricted species to be resolved.

Proton NMR investigation of the influence of subunit assembly on the low-spin in equilibrium high-spin equilibrium of met-azido hemoglobin A

The 1H nuclear magnetic resonance signals for the side-chain labile protons of the proximal His-F8 in met-azido derivatives of the isolated chains and intact tetramer of hemoglobin have been identified. Assignment of the two peaks to the individual subunits of the intact tetramer was effected by the basis of the strong similarity of shift of one of the two peaks to that of met-azido semi-hemoglobin, where hemes occupy primarily the alpha subunits, with the heme cavity vacant in the adjacent beta subunits. The magnitudes of the hyperfine shift for both the His-F8 ring NH and the heme methyls reflect the degree of high-spin character in the thermal spin equilibrium between the high-spin, S = 5/2, and low-spin, S = 1/2, states. The changes in these shifts upon tetramer assembly demonstrate that formation of the intersubunit contacts in the R-state met-azido hemoglobin from the isolated chains causes a slight decrease in high-spin character of the alpha (22 to 20%) and a marked increase (5 to 11%) in the high-spin character of the beta subunits. The changes in spin-character are interpreted in terms of slight increase and decrease in the strength of the iron-His F8 bond upon tetramer assembly in the alpha and beta subunits, respectively. These changes in axial bonding upon forming R-state intersubunit contacts are consistent with previous observation on forming the R-state deoxy Hb tetramer from the isolated chains (Nagai, K., La Mar, G.N., Jue, T. and Bunn, H.F. (1982) Biochemistry 21, 842-847).

Photoreactive cardiolipin analogues

New photoreactive analogues of cardiolipin have been chemically synthesized. Photoreactive aryl azido acyl groups were placed at two different locations within the cardiolipin molecule: at the 2-sn position of the 2-sn glycerol of cardiolipin; at the 2-sn position of the 3-sn-phosphatidyl group; or at both locations to provide a dual labeled analogue. Thus three different cardiolipin analogues distinguished by the positions of the aryl azido acyl groups were prepared. Two different aryl azido acyl groups were employed in the above syntheses and the site of acylation was stereospecifically identified using several phospholipids of known specificity for cardiolipin. Acylation of cardiolipin with the symmetrical anhydride of either acyl aryl azido fatty acid analogue, 2-(N-4-azido-2-nitrophenyl)beta-alanine or 12-(N-4-azido-2-nitrophenyl)aminododecanoic acid provided 1-(3-sn-phosphatidyl)-2-(acyl aryl azido)-3-(3-sn-phosphatidyl)-sn-glycerol. Acylation of monolysocardiolipin (1-(3-sn-phosphatidyl)-3-(1-acyl-2-lyso-glycero(3)phospho)-sn-glyce++ + rol provided two products. 1-(3-sn-phosphatidyl)-3-(1-acyl-2-(acyl aryl azido)-glycero(3)phospho)-sn-glycerol and the doubly labeled 1-(3-sn-phosphatidyl)-2-(acyl aryl azido)-3-(1-acyl-2-(acyl aryl azido)glycero(3)phospho)-sn-glycerol. These are the first reported photoreactive analogues for cardiolipin. The analogues were positive effectors for cytochrome P-450sec, and as shown by SDS-PAGE, they labeled the single subunit of cytochrome P-450sec and the smallest subunits of cytochrome c oxidase from beef heart.

Monoconjugated bilirubin is a major component of hemolysis-induced gallstones in mice

The role of bilirubin conjugates in the formation of pigment gallstones is not known. In this study, we completely solubilized and then analyzed by high-performance liquid chromatography specimens of black pigment gallstones from eight nb/nb mice with hereditary hemolytic anemia. Each dried gallstone specimen of about 200 micrograms was dissolved in 5 ml of dimethyl sulfoxide/0.15 M HCI/50 mM disodium-EDTA (8:1:1 by volume) at room temperature. Stone dissolution was complete by 30 min as monitored by the A456 and direct observation, and no oxidative products of bilirubin were observed in the visible spectrum, 350 to 750 nm. By high-performance liquid chromatography, the intact tetrapyrroles were separated as diconjugated and monoconjugated bilirubins; unconjugated bilirubin was resolved as XIII, IX and III alpha-isomers. The isocratic solvent system used was 0.1 M di-n-dodecylamine acetate/0.1 M di-n-octylamine acetate (4:1, v/v) in methanol, pH 7.4, at a flow of 1 ml per min. Diconjugated bilirubin accounted for 6.0 +/- 2.4 molar % (mean +/- S.E.), monoconjugated bilirubin for 37.4 +/- 8.4% and unconjugated bilirubin for 56.3 +/- 8.9% of the solubilized pigments. The IX alpha-isomer represented 96 +/- 1.9% of the unconjugated bilirubin. The presence of bilirubin conjugates in gallstones was confirmed by ethylanthranilate diazotization: the conjugated azodipyrrole in stone had the same retention time as that of conjugated azodipyrrole from rat and mouse bile. A majority of the bilirubin conjugates was sensitive to beta-glucuronidase of liver origin, indicating that the C-1 glucuronide ester was present.(ABSTRACT TRUNCATED AT 250 WORDS)

[Suicide with sodium azide]

A case report is presented of the suicide of a 27-year-old female laboratory assistant by means of sodium azide. Simple colorimetric and volumetric methods are present to detect and estimate the salt.

Specific detection and determination of azide in wine

In view of false-positive results obtained with the azide-detection method based on complex-formation with ferric ions, a specific liquid-chromatographic azide determination was adapted for the analyses of wine. The samples are distilled free of alcohol under alkaline conditions and acidified, and a new distillate is collected. The distillate is buffered (pH 4.7) and treated with 3,5-dinitrobenzoylchloride and the derivative thus formed is detected and determined by HPLC.

Insulin receptors in isolated human adipocytes. Characterization by photoaffinity labeling and evidence for internalization and cellular processing

We photolabeled and characterized insulin receptors in isolated adipocytes from normal human subjects and then studied the cellular fate of the labeled insulin-receptor complexes at physiologic temperatures. The biologically active photosensitive insulin derivative, B2(2-nitro-4-azidophenylacetyl)des-PheB1-insulin (NAPA-DP-insulin) was used to photoaffinity label the insulin receptors, and the specifically labeled cellular proteins were identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and autoradiography. At saturating concentrations, the binding of 125I-NAPA-DP-insulin to the isolated adipocytes at 16 degrees C was rapid (half-maximal in approximately 1 min and maximal in approximately 10 min) and approximately 25% of the specifically bound ligand was covalently linked to the cells by a 3-min exposure to long-wave (366 nm) ultraviolet light. Analysis of the photolabeled cellular proteins by PAGE in the absence of disulfide reductants revealed the specific labeling of a major protein band of Mr 330,000 and two less intense bands of Mr 295,000 and 260,000. Upon reduction of disulfide bonds with dithiothreitol, all three unreduced forms of the insulin receptor were converted into a major labeled Mr-125,000 band and a less intensely labeled Mr-90,000 band. The labeling of the Mr-125,000 receptor subunit was saturable and native porcine insulin effectively inhibited (half-maximal inhibition at 12 ng/ml) the photolabeling of this binding subunit by NAPA-DP insulin. When intact adipocytes photolabeled at 16 degrees C (a temperature that inhibits endocytosis) were immediately trypsinized, all of the labeled receptor bands were converted into small molecular weight tryptic fragments, indicating that at 16 degrees C all of the labeled insulin-receptor complexes remained on the cell surface. However, when the photolabeled cells were further incubated at 37 degrees C and then trypsinized, a proportion of the labeled receptors became trypsin insensitive, indicating that this fraction has been translocated to the cell interior and thus was inaccessible to the trypsin in the incubation medium. The intracellular translocation of the labeled receptors was observed within 2 min, became half-maximal by 10 min, and maximal by approximately 30 min of incubation at 37 degrees C. Cellular processing of the internalized insulin-receptor complexes also occurred, since incubation at 37 degrees C (but not 16 degrees C) resulted in the generation of a Mr-115,000 component from the labeled receptors. Inclusion of chloroquine, a drug with lysosomotropic properties, in the incubation media caused a time-dependent increase (maximal increase of 50% above control by 2 h at 37 degrees C) in the intracellular pool of labeled receptors. In contrast to these findings in human adipocytes, no appreciable internalization of insulin-receptor complexes and no chloroquine effect was observed in cultures human IM-9 lymphocytes during a 1-h incubation at 37 degrees C. We concluded that in isolated human adipocytes: (a) the subunit structure of insulin receptors is the same as that reported for several other tissues, (b) insulin-receptor complexes are rapidly internalized and processed at physiologic temperatures, and (c) the cellular processing of insulin-receptor complexes occurs at one or more chloroquine-sensitive intracellular site(s).

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.

Gas chromatographic determination of hydrazoic acid

A gas chromatographic procedure was developed for the determination of hydrazoic acid. Two possible columns were evaluated. The limits of detectability were 1.5 ng, or approximately 0.05%, in aqueous solution (w/v) and 2 mg per liter in air.

Nuclear magnetic resonance titration curves of histidine ring protons. Human metmyoglobin and the effects of azide on human, horse, and sperm whale metmyoglobins

Four titrating histidine ring C2 and C4 proton resonances are observed in 220 MHz proton NMR spectra of human metmyoglobin as a function of pH. Values of ionization constants determined from the NMR titration data using an equation describing a simple proton association-dissociation equilibrium are curves (1) 6.6, (2) 7.0, (3) 5.8, and (4) 7.4. Four histidine residues have also been found to be solvent-accessible in human metmyoglobin by carboxymethylation studies (Harris, C.M., and Hill, R.L. (1969) J. Biol. Chem. 244, 2195-2203). Two of the titration curves (3 and 4) deviate significantly from the chemical shift values normally observed for histidine C2 proton resonances. Curve 3, with a low pKa, is shifted downfield at high values of pH and also exhibits a second minor inflection with a pKa value of 8.8. On the other hand, the high pKa curve, 4, is shifted upfield at all values of pH. The characteristics of the NMR titration curves with the lowest and highest pKa values (3 and4) are very similar to curves observed previously with sperm whale and horse metmyoglobins (Cohen, J.S., Hagenmaier, H., Pollard, H., and Schechter, A.N. (1972) J. Mol. Biol. 71, 513-519). These results indicate that the histidine residues from which these curves are derived have unusual and characteristic environments in this series of homologous proteins. The NMR spectra of all three metmyoglobins are changed extensively as a result of azide ion binding, indicating conformational changes affecting the environments of several imidazole side chains. The presence of azide ion causes a selective downfield chemical shift for the low pKa curve and a selective upfield chemical shift for the high pKa curve in all three proteins. Azide also abolishes the second inflection seen in the low pKa curve at high pH. In addition to these effects, the presence of azide ion permits the observation of two additional titrating proton resonances for all three metmyoglobins. Increasing the azide to protein ratio at several fixed values of pH yields results which show that a slow exchange process is occurring with each of the metmyoglobins. In the azide titration studies the maximum changes in the NMR spectra occurred at approximately equimolar concentrations. The NMR results for these proteins in the absence and presence of azide ion are related to x-ray crystallographic studies of sperm whale metmyoglobin and the known alkylation properties of the histidine residues. Tentative assignments of the titrating resonances observed are suggested.

An inhibitor to erythrocyte agglutination in bovine albumin preparations

Three out of 28 commercial preparations of bovine serum albumin have been encountered which have an inhibitory effect on the assay of anti-Rh-o(D) using the Technicon AutoAnalyser. The inhibitory property, which can also be demonstrated by standard manual serological techniques, appears to be directed towards the second stage of the agglutination reaction. An automated screening procedure for bovine serum albumin preparations and some properties of the inhibitor are described.