Showing papers on "Iodide published in 1971"

Solute perturbation of protein fluorescence. The quenching of the tryptophyl fluorescence of model compounds and of lysozyme by iodide ion.

Abstract: The effect of iodide on the tryptophyl fluorescence of model compounds and of lysozyme was studied in order to evaluate the factors that determine the use of iodide as a selective quencher of the fluorescence of tryptophyl side chains of proteins exposed to solvent. The results with the model compounds indicate the involvement of a collisional quenching mechanism due to the agreement with the Stern-Volmer law and the proportionality of the quenching constant with To7 for indole-3-acetamide. Bimolecular rate constants, k a , calculated from measured quenching constants using available lifetime data are equal to, greater than, or less than 4-6 X lo9 M-' sec-l for uncharged, positively charged, and negaI n a preliminary study it was shown that a large fraction of the tryptophyi fluorescence of lysozyme in aqueous solution was quenched by low concentrations of iodide ion (Lehrer, lY67). It was concluded from a study of the magnitude of the quenching of fluorescence and the character of the difference fluorescence spectrum produced in the presence and absence of substrate that the fluorescence of tryptophyls exposed to solvent and located in the substrate binding site was preferentially quenched by iodide. It appeared that this technique, which can be called solute perturbation of protein fluorescence, could be used as a probe of fluorophor exposure in proteins in a manner analogous to the technique of solvent perturbation of protein absorption (Herskovits and Laskowski, 1960; Laskowski, 1966). * From the Department of Muscle Research, Boston Biomedical Research Institute, Boston, Massachusetts 021 14, and from the Department of Neurology, Harvard Medical School, Boston, Massuchusetts 02115. Receired April 22, 1971. This work was supported by grants from the National Institutes of Health (AM 11677 and HE 0581 1) and the iMass'ichuserts Heart Association (516). tively charged tryptophyl compounds, respectively. A modified version of the Stern-Volmer law was calculated for a fluorophor population with different quantum yields and quenching constants. This formulation allows the calculation of the effective quenching constant from the intercept and the slope at low iodide concentration of a F o ] M cs. l/(I-) plot. Data obtained for lysozyme indicate that for the native protein about one-half the tryptophyl fluorescence is accessible at pH 5.3 whereas all of the tryptophyl fluorescence is accessible in 6 M G d n . HCI. Information regarding the presence of charged groups near tryptophyl side chains was obtained for lysozyme by studying the dependence of the quenching on pH. More recently, studies by other workers have ~ised bromate (Winkler, 1969) and iodide (Arrio er al., 1970) to quench extrinsic fluorescence (Teale and Badley, 1970). Oxygen has also been used as a quencher of pyrenebutyric acid bound to proteins (Vaughan and Weber, 1970). Burstein (1968a) has also independently studied the quenching of tryptophyl fluorescence in model compounds by iodide. In order to learn more about the quenching mechanism and the factors which determine fluorophor exposure, various tryptophyl model compounds and a model protein, lysozyme. were used in the present study. The results of the model compound study provide evidence for a mechanism that follows the classical Stern-Volmer law (1919), predominantly involving collisional quenching, and illustrate the importance of local charge and solvent viscosity. The quenching of lysozyme fluorescence by iodide also appears to follow a similar mechanism because of the agreement obtained with a inodified version of the Stern-Volmer law which was calculated for a heterogeneous distribution of fluorophors in a protein. Effective Stern-Volmer quenching constants and values for the fractional accessible fluorescence were obtained for lyso3254 B I O C H E M I S T R Y , V O L . 1 0 , N O . 1 7 , 1 9 7 1 I O D I D E Q U E N C H I N G O F P R O T E I N F L U O R E S C E N C E zyme in 6 M Gdn.HCI, 'S M urea, and in aqueous solution at different pH's using the modified Stern--Volmer law. Values obtained are consistent with information regarding accessibility obtained by other methods. Experimental Section Muteriais. The following high-purity compounds were used as obtained from Mann Research Laboratories, New York, N. Y. : indole-3-acetic acid, indole-3-propionic acid, indole-3-butyric acid, indole-3-acetamide, N-Ac-L-TrpNH?, L-TrpOEt, Gdn . HCI, and urea. L-Trp (Cyclo Chemical Corp., Los Angeles), KI , Na&03, citric acid, and NaCl (Fisher Scientific Co., Freehold, N. J.) were all of high purity and used as obtained. Indole (Fisher) and skatole (3-methylindole) (Mann) were recrystallized from methanol containing Norit A (Matheson Coleman & Bell, Rutherford, N. J.). Hepes buffer was used as obtained from Calbiochem (Los Angeles). Poly(Glug9Trp1) and poly(Lysg7Trp3) were high molecular weight random sequence copolymers kindly supplied by Dr. G. Fasman. Lysozyme from two different sources were used (twice crystallized from Worthington Biochemical Corp., Freehold, N. J., and six-times crystallized from Miles Laboratories, Elkhart, Ind.). Both preparations gave similar results. Ac3Glcn was kindly supplied by Dr. J. Rupley and glycol chitin was obtained from Miles Laboratories. Methods. Quenching measurements at constant pH were made on five solutions of a given material containing increasing amounts of K I (0-0.2 M). These were prepared by diluting stock solutions of the model compound, of KI, of NaC1, and of buffer, into volumetric flasks. NaCl was used to keep the ionic strength constant. Stock solutions of the indole compounds were used within a few days of preparation and kept in the dark at 0-5" overnight. A small amount of SO3?(ca. M) was added to the iodide solution to prevent 1 3 formation. This was necessary because Isabsorbs in the wavelength region of tryptophyl fluorescence (filter effect) and because of possible chemical reaction. The solutions were equilibrated at 25 O before the measurements. Stock solutions of lysozyme were routinely filtered through a Millipore filter (HAWP 0.45 p ) before use. pH titrations were performed in the absence and presence of iodide by adding small quantities of 0.5 M HC1 to the solution in the cuvet, which contained 2 mM Hepes and 2 mM citrate, originally pH 8, then measuring the pH and fluorescence. pH was measured with a Radiometer PHM4c meter standardized at pH 4 and 7. Fluorescence spectra and intensities were measured by exciting a t 280 nm or longer. In most cases no corrections for iodide absorption were necessary. The fluorescence of a reference (usually the 0.2 M NaC1-0.0 M K I solution) was measured just before measuring the fluorescence of each solution in order t o correct for any exciting lamp fluctuation. Fluorescence measurements were made with either an Aminco-Bowman spectrofluorometer or an instrument that employs two Jarrell-Ash 0.25-m monochromators, an EM1 9601 B photomultiplier, and either a high-pressure 200-W mercury lamp or a 150-W high-pressure xenon lamp. Low temperatures were obtained with a refrigerated water circulator attached to the sample housing. The temperature was measured by inserting a calibrated thermistor into the sample solution. Abbreviations used are: Gdn . HCI, guanidine hydrochloride; Trp, tryptophyl or tryptophan; Hepes, N-2-hydroxyethylpiperazine-N'2-ethanesulfonic acid ; Ac3GIcii. tri-N-acetyl-D-glucosamirie. The activity of lysozyme was determined by the method of Hamaguchi et a/ . (1960). The decrease in viscosity with time caused by hydrolysis of glycol chitin (2 mg/ml) by lysozyme (0.02 mg/ml) in the presence of 0.2 M NaCl or 0.2 M KI in 2 m M citrate (pH 5.5) is the basis of this method. The specific viscosity of glycol chitin solutions in Cannon viscometers at 25" was measured with time after a small volume of lysozyme was added. The slope of the approximately linear viscosity decrease between 1 and 10 min was used as a measure of activity. The optical rotatory dispersion and circular dichroism spectra of lysozyme (0.95 mg/ml) in 0.2 M NaCl or in 0.2 M KI , 2 mM citrate (pH 5.2) were measured in a 1-cm cell with a Jasco spectropolarimeter. The absorbance of Iprevented measurements below 265 nm. Difference spectra were either measured with a Cary 15 or a Beckman DK spectrophotometer using mixing cells (Pyrocell, Inc., N. Y . ) . The total absorption over the wavelengths scanned was always below 2.2. The low-temperature studies were performed with a Beckman D K using a refrigerated sample holder.

Enzymic iodination. A probe for accessible surface proteins of normal and neoplastic lymphocytes.

Abstract: 1. Radioactive iodide was covalently bound to living cells from normal mouse spleen and a variety of lymphoid tumours by a system consisting of lactoperoxidase, hydrogen peroxide and iodide. 2. About 3×10 5 -6×10 5 molecules of [ 125 I]iodide/cell could be incorporated without affecting cell viability. 3. Electron-micrographic radioautography showed that the radioactive label was associated with the outer surfaces of the cells. 4. Radioiodinated proteins were solubilized in 9m-urea–0.2m-mercaptoethanol and analysed by gel-filtration and disc electrophoresis. 5. Comparison of distinct tumour lines by disc electrophoresis showed qualitative and quantitative differences in protein distribution patterns.

Analytical Study of the Lead Ion-selective Ceramic Membrane Electrode

Abstract: The lead(II) ion-selective ceramic membrane electrode developed by sintering a mixture of lead, silver, and cuprous sulfides showed sensitivity, selectivity, and other response characteristics well suited to analytical utilization. The Nernstian slope was obtained over a concentration range from 10−1 to 10−6M Pb2+ in activity, and the analytical range had a concentration of 10−1–10−7M when the membrane contained less than 30 wt% of cuprous sulfide and more than 1 wt% of lead sulfide. Among the common ions, silver, cupric, mercury(II), ferric, sulfide and iodide ions interfered seriously. About 10 times as many cadmium and bromide ions and more than 1000 times as many alkali metal, alkaline earth metal, zinc, aluminum, nickel, manganese(II), cobalt, and nitrate ions did not interfere with the lead ion, however. The electrode potentials did not change over a pH range from 2 to the pH at which the precipitation of lead hydroxide occurred. The electrode was safely used at temperatures from 0 to 95°C, and the ...

Dielectric relaxation in non aqueous solutions. Part 2.—Solutions of tri(n-butyl)ammonium picrate and iodide in polar solvents

Abstract: The permittivity and loss of solutions of tri(n-butyl)ammonium picrate and iodide in various polar solvents have been measured at a number of frequencies between 0.2 and 3.0 GHz. The relative static permittivities of the pure solvents used range from 3.37 to 20.7 at 25°C. For all the solutions investigated, the observed dispersion of permittivity is adequately described by a single relaxation time, which for a given solvent depends on the concentration as well as the nature of the solute. Apparent dipole moments evaluated from the dispersion amplitude by means of Bottcher's theory, on the assumption that the dipole occupies a spherical cavity, are 12.3±0.4 D and 11.2±0.6 D for the picrate and iodide respectively. These values indicate that the relaxing dipole is an ion pair. Dielectric relaxation times corrected for internal field effects by different relations are compared with those calculated from the partial molar volume of the solute and the viscosity of the solvent by means of the Debye-Stokes equation. Density data for solutions of the two salts in 1,2-dichloroethane are included and from these data, partial molar volumes of the salts have been evaluated.

Iodine in the surface water of the ocean

Abstract: Iodine in sea water of the Pacific was determined with special interest in the relation between iodide and iodate in the surface water of the ocean. The result was discussed with reference to the mechanism of iodide formation proposed byTsunogai andSase. The concentration of iodide varies widely from the lower value than the detection limit to 0.21μg at./l, while the concentration of total iodine is nearly constant and the mean value is 0.41μg at./l. The vertical profile of iodide often shows the maximum in the surface layer. In the surface layer, the concentration of iodide is higher in warm water (0,10μg at./l on the average) than that in cold water of lower temperature than 20° C (0.03μg at/l). The highest concentration of iodide among the warm waters is found in the surface water of the equatorial area (0.13μg at./l) where the biological productivity is also high. Iodide is generally more enriched in the water having higher biological activity even in the cold water. These results are considered to be compatible with the mechanism of iodide formation proposed.

Lead Iodide Nuclear Particle Detectors

Abstract: Semiconductor nuclear particle detectors have been made from lead iodide. α particles and γ quanta have been counted in the temperature range from −200 to +130°C. From α‐particle pulse height the μτ+ product has been estimated to be 2×10−8 cm2/V.

α–γ transition in nylon 6

Abstract: The α to γ transition that occurs in nylon 6 upon iodine treatment was investigated by infrared spectroscopy, differential thermal analysis, and x-ray diffraction techniques. Thin films of nylon (0.2 mil) were treated in either iodine–potassium iodide aqueous solution or in iodine vapor. Very short treatment times, in the order of 30 sec, were found to effect the transition when a solution 0.5M with respect to iodine was used. The infrared spectra of the iodine nylon complexes formed from either the α- or γ-nylon 6 treated in vapor or dissolved iodine were all similar. This is an indication that molecular iodine is the active species in forming the complex. The temperature of the washing solution used to remove the iodine from the nylon determines whether an α-nylon 6 or γ-nylon 6 is obtained from the complex after washing. Nylon 6 plaque surfaces and thin films are similar in their behavior towards the iodine treatment. The γ-nylon 6 is a stable modification at all temperatures below its melting point. The conversion of the γ form back to the α modification can occur only if the hydrogen bonding is severely affected, e.g., by phenol treatment, iodine treatment, melting, etc. Infrared spectroscopy provided no evidence for an α–γ transition in nylon 6 on heating the sample continuously through its melting point. The shapes of the melting peaks in the above two modifications of nylon 6 were sufficiently different to provide a means of identifying the two crystalline forms.

Concentration of 35S-propylthiouracil by the thyroid gland and its relationship to anion trapping mechanism.

Abstract: Propylthiouracil is concentrated by the thyroid gland in rats and man. Four 35 S compounds were demonstrated in the rat and human thyroid by thin-layer chromatography: sulphate, intact propylthiouracil, an unknown metabolite X and origin 35 S activity which is protein bound. Unbound 35 S compounds in plasma include propylthiouracil, the glucuronide conjugate of PTU, sulphate, and X. The thyroid concentration rather than the plasma level of propylthiouracil determines the duration of inhibition of organic binding of iodine in the thyroid. The effect of perchlorate and iodide on the thyroid concentrating mechanism for 35 S-propylthiouracil and 125 I-iodide was studied. The level of perchlorate and iodide which almost completely blocked the concentration of 125 I-iodide also partially reduced the concentration of 35 S-propylthiouracil. Iodide but not perchlorate decreased the rate of metabolism of 35 S-propylthiouracil in the thyroid gland.

Energy transduction in mitochondrial fragments. Interaction of the membrane with acridine dyes.

Abstract: Atebrin and acridine orange fluorescence and absorbance characteristics are sensitive to their environment. Anions, such as iodide, nitrate or chloride strongly decrease acridines fluorescence, while sulfate or acetate are much less effective. Energization by succinate or ATP of rat liver mitochondrial fragments produces a fluorescence decrease of atebrin, only in the presence of iodide, nitrate or chloride. In the presence of sulfate or acetate or in the absence of anions, no changes are detected. Binding changes of acridines are also observed in association with energy conservation in mitochondrial fragments in the presence of iodide, nitrate or chloride. These data are consistent with a model in which the membrane of mitochondrial fragments, becoming more positive than the medium when energized, creates local electrolyte concentration changes affecting fluorescence, absorbance and binding properties of acridine dyes.

Some quantitative aspects of the labelling of proteins with 125I by the iodine monochloride method

Abstract: The labelling of proteins by the iodine monochloride method was studied by using a mathematical model. The equations used were primarily derived from the mass law equation of the isotopic exchange reaction between [(125)I]iodide and iodine monochloride. For convenient application, all equations were programmed into a computing desk-top calculator. To support the validity of the theoretical model, a series of iodinations of insulin were performed under various labelling conditions. The results of these experiments compare well with the theoretically derived values. Deviations from the theoretical values occurring at molar ratios of [(125)I]iodide to iodine monochloride 4.0 are explained and suggestions made about how to prevent them. The mathematical model was used to simulate the isotopic exchange, and the iodination reaction under various conditions, to study (a) the influence of the amount of [(125)I]iodide on the amount of [(125)I]iodine monochloride formed, (b) the influence of the specific radioactivity of [(125)I]iodide on the amount of [(125)I]iodine monochloride formed, and (c) the influence of the specific radioactivity of [(125)I]iodide on the number of millicuries needed for labelling to a desired extent.

Effect of Temperature on, and Reproducibility of, the Charge Transfer to Solvent Spectrum of Aqueous Iodide

Abstract: THE energy Emax of the first absorption maximum for the charge-transfer-to-solvent (c.t.t.s.) spectrum of iodide in water (Emax ≡ hvmax = hc/λmax; λmax in water is near 230 nm) is particularly sensitive to changes in the environment, that is, temperature1, pressure2,3 and added co-solvent1,2. A recent review5 gives theoretical models and applications of charge-transfer-to-solvent spectra. The energy Emax for the first c.t.t.s. band of aqueous iodide is known to shift to lower values as the temperature of the solution is raised6. For iodide in other solvents Emax has always been reported to be linearly dependent on temperature1,5. Recently, however, values for Emax of iodide in water have been published that show deviations from linearity outside of experimental errors5,7, namely, thermal anomalies somewhat similar to those reported by Drost-Hansen et al. for other properties of aqueous solutions8. The existence of these anomalies in the Emax against T curve has, however, been denied9.

Elevated salivary iodine and salivary gland enlargement due to iodinated contrast media.

Abstract: After each of 3 intravenous urographic examinations a patient with advanced renal failure developed salivary gland enlargement.Total iodine and free iodide concentrations were measured in mixed saliva and in plasma collected while he had sialadenopathy.These measurements revealed high concentrations of both organically bound iodine and free iodide in the saliva at a time when the plasma diatrizoate level was high.The findings suggest secretion of contrast media by the salivary glands, concomitant with the secretion of free iodine split off of the organic contrast molecule.

IRON (II)-AND MANGANESE(I)-CARBORANE COMPLEXES FORMED THROUGH METAL-CARBON sigma-BONDS.

Abstract: : Reaction of 1-lithiocarboranes with manganese pentacarbonyl bromide and cyclopentadienyl iron dicarbonyl iodide gives rise to a series of stable neutral derivatives containing a metal-carbon sigma-bond. Reaction of 1,10-dilithio-1,10-dicarba-closo-decaborane(10), formed from 1,10-dicarba-closo-decaborane(10) and two mole equivalents of n-butyllithium in ethereal solvents, with 2 mole equivalents of cyclopentadienyl iron dicarbonyl iodide, gives rise to an analogous derivative containing two non-chelating metal-carbon sigma bonds. The preparation, characterization, reactions, and proposed structures of these complexes are discussed. (Author)