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PubMed1995

PSGL-1 recognition of P-selectin is controlled by a tyrosine sulfation consensus at the PSGL-1 amino terminus.

P-selectin binding to neutrophils requires a specific protein, P-selectin glycoprotein ligand 1 (PSGL-1), as well as sialyl-Lewis X (sLex) glycan determinants. We have found that a short segment near the amino terminus of PSGL-1 that contains a tyrosine sulfation consensus is essential for P-selectin adhesion and that addition of the amino-terminal segment to some but not all mucin-like molecules confers on those molecules the ability to bind P-selectin. PSGL-1 synthesized in the presence of sulfation inhibitors binds P-selectin weakly, and within the amino-terminal 20 residues, mutation of the tyrosines to phenylalanine abolishes binding. Rolling of HL-60 cells on P-selectin-coated coverslips is strongly attenuated by treatment of cells with an inhibitor of sulfation.

Amino Acid Sequence↗
PubMed1993

Effects of various salts on the steady-state enzymatic activity of E. coli alkaline phosphatase.

Seventeen salts were tested at various concentrations for their effects on E. coli alkaline phosphatase steady-state activity. Three effects were distinguished: a general ionic strength effect, and weaker cation and anion effects. 1. All salts tested, including those with "noninteracting" cations and anions, stimulate alkaline phosphatase activity usually ca. 100% at moderate (0.05-0.3 M) concentrations. 2. Cations such as Na+ and Li+ produce further increases in activity at concentrations up to 1 M. The noninteracting cations tetramethylammonium and tetrapropylammonium produce lower activities at these concentrations. These do not provide the secondary stimulatory effect of cations such as Na+ or Li+. 3. Anions associated with greater "salting in" effectiveness such as thiocyanate also reduce activity at ca. 1 M concentrations. These latter effects are not dependent on protein concentration so they probably do not involve subunit dissociation. There is little effect on the fluorescence or fluorescence-polarization spectrum of the enzyme so there is no general effect of 1 M salts on the conformation of the protein. The Michaelis constant for the substrate, p-nitrophenylphosphate, and inhibition constant for inorganic phosphate are increased to some extent by salts, but the increase in activity is due to an increase in Vmax. Our working hypothesis is that increased ionic strength weakens electrostatic interactions, enabling noncovalently bound phosphate to dissociate more rapidly.

Alkaline Phosphatase↗
PubMed1987

Hydrophobic stabilization of chiton hemocyanins: effects of ureas, Hofmeister salts and pH on their dissociation.

The subunit dissociation of the hemocyanins from five members of the Polyplacophora families, Acanthochitonidae, Callistoplacidae, Chitonidae, Ischnochitonidae and Mopalidae, represented by the chitons Cryptochiton stelleri, Nutallina fluxa, Acanthopleura granulata, Stenoplax conspicua and Mopalia mucosa, respectively, have been investigated by light-scattering molecular-weight and ultracentrifugation methods, using the hydrophobic reagents of the urea series and the Hofmeister salt series as probes of the contact areas of the hemocyanin subunits. The polyplacophoran hemocyanins are decamers with molecular weights of (4.2-4.6) X 10(6). The effectiveness of dissociation by the ureas follows the order of increasing hydrophobicity of the reagent, i.e., urea, methyl-, ethyl-, propyl- and butylurea, as expected of hydrophobically stabilized subunit systems. The urea dissociation is found to be a two-step reaction: the dissociation of parent decamers to dimers followed by dissociation of the dimers to monomers. Analysis of the observed decrease in molecular weight requires the interaction with urea of about 27 to 35 apparent amino-acid groups (Napp) at the contact areas of the dimers, and a much larger number of apparent binding groups ranging from about 100 to 120 per monomer at the contact areas of the monomers. Fitting of the pH dissociation profiles of A. granulata, C. stelleri, M. muscosa and S. conspicua requires the participation of a much smaller number of amino-acid residues in the interaction with the probe-solvent components. The ionization or protonation of one acidic and one basic group per dimer, and five to eight acidic and basic groups per monomer is found to be adequate for the description of the two-step pH dissociation reaction.

Animals↗
PubMed1987

The B-Z conformational transition and aggregation of poly[d(G-C)] induced by moderate concentrations of Mg(CIO4)2.

Mg(ClO4)2 induces the cooperative B-to-Z transition of poly[d(G-C)]; the salt concentration at the midpoint is 0.26 M. A comparison with previous data for NaCl, MgCl2 and NaClO4 (F.M. Pohl and T.M. Jovin, J. Mol. Biol. 67 (1972) 375) indicates that Mg(ClO4)2 is more effective than would be anticipated from the simple additive effects of the Mg2+ and ClO4- ions (the ionic strengths of the respective transition points are: NaCl, 2.4; MgCl2, 2.1; NaClO4, 1.8 and Mg(ClO4)2, 0.78). These results suggest the importance of specific interactions involving ClO4-, particularly in the presence of Mg2+. The B-Z transition of poly[d(G-C)] can be monitored spectroscopically via the large hyperchromic shift at 295 nm and the inversion in the CD spectrum. The reaction is fully reversible and can be fitted by a monoexponential function with half times varying between 8 and 150 min. The observed relaxation times are strongly dependent on the concentration of Mg(ClO4)2 with a distinct maximum at the transition point, in accordance with a concerted mechanism involving only the B and Z states. As the polymer assumes the Z conformation it progressively aggregates into a gel-like precipitate, which, however, redissolves rapidly upon lowering the salt concentration. The natural DNA from Micrococcus lysodeikticus which has a high GC content of 72% is also precipitated by Mg(ClO4)2 but we do not have direct spectroscopic evidence for the involvement of the Z conformation in this phenomenon. Neither calf thymus DNA (41% GC) nor poly[d(A-T)] (0% GC) aggregates under the same conditions.

Chlorates↗
PubMed1988

The influence of inorganic anions on the formation and stability of Fe3+-transferrin-anion complexes.

Harris (Biochemistry 24 (1985) 7412) reports that inorganic anions bind to human apotransferrin in such a way as to perturb the ultraviolet spectrum. The locus of binding is thought to involve the specific metal/anion-binding sites since no perturbation is observed with Fe3+-transferrin-CO3(2-). Paradoxically, we were unable to demonstrate the formation of Fe3+-transferrin-inorganic anion complexes despite the presence of high concentrations of SO4(2-), H2PO4-, Cl-, ClO4- or NO3-. Similar results were found for human lactoferrin. Electron paramagnetic resonance spectroscopy and visible spectrophotometry were used to monitor the results. An attempt to form the H2PO4- complex by displacement of glycine from Fe3+-transferrin-glycine resulted only in the disruption of the ternary complex. A series of inorganic anions varied in their ability to release iron from Fe3+-transferrin-CO3(2-) at pH 5.5, the approximate pH of endosomes where iron release takes place within cells. The order of effectiveness was H2P2O7(2-) much greater than H2PO4- greater than SO4(2-) greater than NO3- greater than Cl- greater than ClO4-. The rate of iron removal from Fe3+-transferrin-CO3(2-) at pH 5.5 by a 4-fold excess of pyrophosphate was greatly enhanced by physiological NaCl concentration. Iron removal was complete within 10 min, the approximate time for iron release from Fe3+-transferrin-CO3(2-) in developing erythroid cells. Thus, inorganic anions may have a significant effect on the release of iron under physiological conditions despite the fact that such inorganic anions cannot act as synergistic anions. The results are discussed in relation to a special role for the carboxylate group in allowing ternary complex formation.

Anions↗
PubMedDate not supplied

Potential health effects of chlorine dioxide as a disinfectant in potable water supplies.

Chlorination of potable water supplies high in organics may yield carcinogenic compounds such as trihalomethanes. Chlorine dioxide has been proposed as an alternative disinfectant to chlorine. However, chlorine dioxide is a strong oxidant that forms significant amounts of chlorite when added to potable water supplies, and chlorite is similar to nitrite in its molecular structure and may be similar in its mechanism of methemoglobin production. Nitrites and chlorites are thought to act synergistically to produce MetHb. Neonates and persons with G-*-PD deficiency are likely to be unusually susceptible to MetHb formation from these compounds because their red cells lack the metabolic machinery to adequately protect against oxidant stress. Since male blacks represent the largest population in the U.S. to be G-6PD deficient, Black male neonates may represent the group at highest risk to the use of chlorine dioxide as a disinfectant in the nations water supplies.

Adult↗
PubMed1993

Free radical intermediates in the oxidation of flavone-8-acetic acid: possible involvement in its antitumour activity.

The sulphate radical (SO4.-), a model one-electron oxidant, reacts with the antitumour drug flavone-8-acetic acid (FFA) with the rate constant 9.1 x 10(8) dm3mol-1s-1 to yield an uncharged radical that reacts with oxygen (k approximately 1 x 10(9) dm3mol-1s-1). The oxidation of FAA by SO4.- in a steady-state system was found to release carbon dioxide with a yield of 96% relative to that of the SO.4-. The results are interpreted by fast (t1/2 < or = 1 microsecond) and efficient decarboxylation of the FAA radical cation, resulting in a carbon-centred radical. The reaction of the latter with oxygen is a possible source of radical-driven cytotoxic pathways, such as singlet oxygen formation via the Russell mechanism or H-abstraction from lipids. On the basis of the observations in the model system, a possible free radical mechanism for the antitumour action of the drug is suggested.

Antineoplastic Agents↗
PubMed1993

35Cl nuclear quadrupole resonance studies of molecular motions of ClO3- and water diffusion in Ca(ClO3)2.2H2O.

A 35Cl nuclear quadrupole resonance (35Cl-NQR) investigation of polycrystalline Ca(ClO3)2.2H2O is described. The 35Cl-NQR frequencies (vQ) for two resonance lines (vQ1 and vQ2), the spin lattice relaxation time (T1Q) for vQ2 only and the line width delta vQ2 were measured in the temperature range 292-345 K, except for the frequency measured up to 455 K. The observed decrease in the resonance frequencies with increasing temperature permitted the determination of the frequencies of librations of the ClO3- ion about two axes perpendicular to the three-fold axis of the ion mainly responsible for this effect. The temperature dependence of the relaxation time T1Q proved the occurrence of water diffusion and hindered rotation of ClO3- ions. The activation energies of these two molecular motions were determined, and their effect on the electric field gradient at the site of a chlorine nucleus was discussed. Temperature measurements of the line width delta vQ2 confirmed the conclusions drawn from the analysis of T1Q(T).

Calcium Compounds↗
PubMed2006

Effect of drug particle size in ultrasound compacted tablets. Continuum percolation model approach.

The main objective of this work is to study the influence of the drug particle size on the pharmaceutical availability of ultrasound compacted tablets. Inert matrix systems containing different drug particle sizes were prepared using both, an ultrasound-assisted press and a traditional eccentric machine. Potassium chloride was used as drug model and Eudragit RS-PM as matrix forming excipient. The excipient particle size was kept constant. The cross-sectional microphotographs of ultrasound tablets show the existence of a quasi-continuum medium. Keeping constant the drug load, US-tablets showed very similar release rates, whereas for traditional tablets, an increase in the particle size resulted in a clear decrease in the release rate. In these tablets, the excipient forms an almost continuum medium. In an infinite theoretical system of these characteristics, the size of the drug particles will not modify the percolation threshold. The percolation of the excipient in this system can be assimilated to a continuum percolation model. In accordance with the proposed model, a lower influence of the drug particle size on the drug release rate was obtained for the US-tablets in comparison with traditional tablets. This fact can be indicative of the similarity of the drug percolation thresholds in these systems.

Acrylic Resins↗
PubMed2006

Thermodynamic assessment of Hg(II)-gibbsite interactions.

As discrete particles and/or as surface coatings on other minerals in natural systems, aluminum hydroxides are efficient sinks for Hg(II). The Hg(II) adsorption on gibbsite was determined as a function of temperature (T), pH, and the type of background electrolytes, i.e., NaNO(3), NaClO(4), and NaCl. When the equilibration time t(E) approximately 2 h, the Hg(II) retention on gibbsite was found to be a reversible process, which was ascribed to adsorption. The Hg(II) adsorption capacity, i.e., Gamma(Hg(II)), varied with the type of electrolyte used in accordance with the following order: Gamma(NO(3))(Hg(II)) > or = Gamma(ClO(4))(Hg(II)) > or = Gamma(Cl)(Hg(II)). In all cases, the estimated thermodynamic parameters showed that the Hg(II) adsorption on gibbsite was endothermic and spontaneous. The Hg(II) adsorption data were quantified with the Langmuir or Hill, and Dublin-Radushkevick (DR), isotherms at all temperatures and acidity levels examined. Always, the Hg(II) adsorption data were in compliance with the DR model. However, the Hg(II) adsorption in NaNO(3) or NaClO(4) was interpreted in terms of the Langmuir model. When NaCl was used as electrolyte, the Hg(II) adsorption was modeled well with the Hill equation. The mean free energy values calculated from DR plots concluded that Hg(II)-gibbsite interactions are a result of chemical bonding.

Adsorption↗
PubMed1989

Purification and properties of the intact P-700 and Fx-containing Photosystem I core protein.

The intact Photosystem I core protein, containing the psaA and psaB polypeptides, and electron transfer components P-700 through FX, was isolated from cyanobacterial and higher plant Photosystem I complexes with chaotropic agents followed by sucrose density ultracentrifugation. The concentrations of NaClO4, NaSCN, NaI, NaBr or urea required for the functional removal of the 8.9 kDa, FA/FB polypeptide was shown to be inversely related to the strength of the chaotrope. The Photosystem I core protein, which was purified to homogeniety, contains 4 mol of acid-labile sulfide and has the following properties: (i) the FX-containing core consists of the 82 and 83 kDa reaction center polypeptides but is totally devoid of the low-molecular-mass polypeptides; (ii) methyl viologen and other bipyridilium dyes have the ability to accept electrons directly from FX; (iii) the difference spectrum of FX from 400 to 900 nm is characteristic of an iron-sulfur cluster; (iv) the midpoint potential of FX, determined optically at room temperature, is 60 mV more positive than in the control; (v) there is indication by ESR spectroscopy of low-temperature heterogeneity within FX; and (vi) the heterogeneity is seen by optical spectroscopy as inefficiency in low-temperature electron flow to FX. The constraints imposed by the amount of non-heme iron and labile sulfide in the Photosystem I core protein, the cysteine content of the psaA and psaB polypeptides, and the stoichiometry of high-molecular-mass polypeptides, cause us to re-examine the possibility that FX is a [4Fe-4S] rather than a [2Fe-2S] cluster ligated by homologous cysteine residues on the psaA and psaB heterodimer.

Bromides↗