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 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

As model reactions between unsaturated fats and water disinfectants in the GI tract, relative rates of destruction of seven polyunsaturated fatty acids (L, alpha Ln, gamma Ln, Ara, EPA, DH, and DT) by OCl- and NH2Cl were investigated in vitro. Using millimolar solutions of seven PUFAs combined with various OCl- mole ratios, disappearance of PUFAs was followed by UV spectrophotometry at pH = 9.5 and at 35 degrees C via conjugated hydroperoxydienes at 234 nm. While OCl- rapidly destroyed all PUFAs, NH2Cl was inert. Overall second-order rate constants computed for L at increasing times disclosed that the attack on the cis-CH=CHCH2CH=CH moiety by OCl- does not follow simple second-order kinetics. Using a logit-log transform and second-order polynomial regression analysis of L's disappearance in a stoichiometric ([L] = 1.2 mM; [ClO-] = 2.4 mM) mix, data were analyzed by the time ratio method of Schwemer and Frost. These agreed with a sequential system of at least two irreversible second-order reactions having k1 = 15.6 L.mol-1.s-1 and k2 = 2.6 L.mol-1.s-1. Preliminary GC/MS analysis indicated that the initial product is a mix of chlorohydrin isomers. These undergo second addition of HOCl and/or lose halogens and polymerize. Additional minor products were also C5-C9 mono- and bifunctional carboxylates and mixed acid aldehydes. Studies with mol equiv of Cl- - free 36ClO- allowed estimation of covalent binding of Cl by L at various times, supporting the kinetic findings. For other PUFAs of higher degree unsaturation, the complexity of feasible reactions precluded an analogous approach.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Toxicology of drinking water disinfection byproducts from nutrients. Rate studies of destruction of polyunsaturated fatty acids in vitro by chlorine-based disinfectants. 150 66

Human low density lipoproteins (LDL) were incubated with increasing amounts of sodium hypochlorite. A decrease of the number of free amino groups on the LDL surface starts only upon addition of 30-40 moles NaOCl per mole apoB, whereas all detectable SH groups are oxidized after addition of nearly 17-20 moles NaOCl. All hypochlorite-modified LDL samples have a higher electronegative surface charge compared with native LDL as revealed by agarose gel electrophoresis and partition of LDL in an aqueous polyethylene glycol/dextran two-phase system. The more NaOCl is used to alter LDL, the higher is the electrical surface charge. Changes in surface charge are found already at low NaOCl concentrations where no decrease of amino groups is detected. It is assumed that changes in surface charge are caused by the formation of monochloramines and especially at low degrees of modification by a further unknown contribution. An effect on the primary structure of apoB or peroxidation-like changes in NaOCl-altered LDL could not be found under our experimental conditions. The results are discussed with respect to such modifications under in vivo conditions by hypochlorous acid generated in stimulated phagocytosing cells.
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PMID:Modification of low density lipoproteins by sodium hypochlorite. 172 92

1. Properties of anion permeation through the membrane of skeletal muscle fibres of the stingray, Taeniura lymma, were studied with intracellular recording and polarization techniques.2. The Cl conductance of the resting membrane in the normal stingray saline at pH 7.7 is 8-10 times greater than the K conductance.3. The Cl conductance decreases with decreasing external pH, with an apparent pK of 5.3, whereas the K conductance is independent of pH between 4 and 9.4. The Q(10) of the Cl conductance is about 2.0, compared with a value of 1.2-1.4 for the K conductance.5. The Cl conductance is proportional to the external Cl concentration when observed after the fibre is equilibrated in the test solution.6. The permeability sequence obtained by potential measurement is SCN > NO(3) > Cl = Br > I > ClO(3) and the permeability ratio is independent of the mole fraction of anions.7. The conductance sequence determined by total replacement of the external Cl with other anion species differs from the permeability sequence and the conductance observed for partial replacement deviates significantly from that expected from the independence principle.8. Possible mechanisms of anion permeation are discussed.
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PMID:Mechanism of anion permeation through the muscle fibre membrane of an elasmobranch fish, Taeniura lymma. 483

The effects of external anions on gating of Na channels of frog skeletal muscle were studied under voltage clamp. Anions reversibly shift the voltage dependence of peak sodium permeability and of steady state sodium inactivation towards more negative potentials in the sequence: methanesulfonate less than or equal to Cl- less than or equal to acetate less than Br- less than or equal to NO-3 less than or equal to SO2-4 less than benzenesulfonate less than SCN- less than ClO-4; approximately the lyotropic sequence. Voltage shifts are graded with mole fraction in mixtures and are roughly additive to calcium shifts. The peak PNa is not greatly affected. Except for SO2-4, these anions did not change the Ca++ activity of the solutions as measured with the dye murexide. Shifts of gating can be explained as the electrostatic effect of anion adsorption to the Na channel or to nearby lipid. Such adsorption is expected to follow the lyotropic series. Anions also interfere significantly with the response of a Ca-sensitive membrane electrode following the same sequence of effectiveness as the shifts of gating. The lyotropic anions decrease the Ca++ sensitivity and cause anomalously negative responses of the Ca electrode because these anions are somewhat permeant in the hydrophobic detector membrane.
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PMID:Lyotropic anions. Na channel gating and Ca electrode response. 630 98

Myeloperoxidase and eosinophil peroxidase catalyzed the oxidation of bromide ion by hydrogen peroxide (H2O2) and produced a brominating agent that reacted with amine compounds to form bromamines, which are long-lived oxidants containing covalent nitrogen-bromine bonds. Results were consistent with oxidation of bromide to an equilibrium mixture of hypobromous acid (HOBr) and hypobromite ion (OBr-). Up to 1 mol of bromamine was produced per mole of H2O2, indicating that bromamine formation prevented the reduction of HOBr/OBr- by H2O2 and the loss of oxidizing and brominating activity. Bromamines differed from HOBr/OBr- in that bromamines reacted slowly with H2O2, were not reduced by dimethyl sulfoxide, and had absorption spectra similar to those of chloramines, but shifted 36 nm toward higher wavelengths. Mono- and di-bromo derivatives (RNHBr and RNHBr2) of the beta-amino acid taurine were relatively stable with half-lives of 70 and 16 h at pH 7, 37 degrees C. The mono-bromamine was obtained with a 200-fold excess of amine over the amount of HOBr/OBr- and the di-bromamine at a 2:1 ratio of HOBr/OBr- to the amine. In the presence of physiologic levels of both bromide (0.1 mM) and chloride (0.1 M), myeloperoxidase and eosinophil peroxidase produced mixtures of bromamines and chloramines containing 6 +/- 4% and 88 +/- 4% bromamine. In contrast, only the mono-chloramine derivative (RNHCl) was formed when a mixture of hypochlorous acid (HOCl) and hypochlorite ion (OCl-) was added to solutions containing bromide and excess amine. The rapid formation of the chloramine prevented the oxidation of bromide by HOCl/OCl-, and the chloramine did not react with bromide within 1 h at 37 degrees C. The results indicate that when enzyme-catalyzed bromide or chloride oxidation took place in the presence of an amine compound at 10 mM or higher, bromamines were not produced in secondary reactions such as the oxidation of bromide by HOCl/OCl- and the exchange of bromide with chlorine atoms of chloramines. Therefore, the amount of bromamine produced by myeloperoxidase or eosinophil peroxidase was equal to the amount of bromide oxidized by the enzyme. Bromide was preferred over chloride as the substrate for both enzymes.
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PMID:Oxidation of bromide by the human leukocyte enzymes myeloperoxidase and eosinophil peroxidase. Formation of bromamines. 785 68

Polyphenols have been implicated in the virulence and oxidant resistance of Cryptococcus neoformans. Although monomeric polyphenols did not protect against the prooxidant, plumbagin, polymeric dopamine-melanin conferred resistance both to hypochlorite and to permanganate. The physiologic antioxidant capacity conferred by melanin was found to be 21.3 x 10(-15) mole-equivalents per cell, a value which approximates oxidant production by stimulated macrophages.
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PMID:Antioxidant function of fungal melanin. 822 53

Ca(2+)-activated Cl channels (Cl(Ca)Cs) are an important class of anion channels that are opened by increases in cytosolic [Ca(2+)]. Here, we examine the mechanisms of anion permeation through Cl(Ca)Cs from Xenopus oocytes in excised inside-out and outside-out patches. Cl(Ca)Cs exhibited moderate selectivity for Cl over Na: P(Na)/P(Cl) = 0.1. The apparent affinity of Cl(Ca)Cs for Cl was low: K(d) = 73 mM. The channel had an estimated pore diameter >0.6 nm. The relative permeabilities measured under bi-ionic conditions by changes in E(rev) were as follows: C(CN)(3) > SCN > N(CN)(2) > ClO(4) > I > N(3) > Br > Cl > formate > HCO(3) > acetate = F > gluconate. The conductance sequence was as follows: N(3) > Br > Cl > N(CN)(2) > I > SCN > COOH > ClO(4) > acetate > HCO(3) = C(CN)(3) > gluconate. Permeant anions block in a voltage-dependent manner with the following affinities: C(CN)(3) > SCN = ClO(4) > N(CN)(2) > I > N(3) > Br > HCO(3) > Cl > gluconate > formate > acetate. Although these data suggest that anionic selectivity is determined by ionic hydration energy, other factors contribute, because the energy barrier for permeation is exponentially related to anion hydration energy. Cl(Ca)Cs exhibit weak anomalous mole fraction behavior, implying that the channel may be a multi-ion pore, but that ions interact weakly in the pore. The affinity of the channel for Ca(2+) depended on the permeant anion at low [Ca(2+)] (100-500 nM). Apparently, occupancy of the pore by a permeant anion increased the affinity of the channel for Ca(2+). The current was strongly dependent on pH. Increasing pH on the cytoplasmic side decreased the inward current, whereas increasing pH on the external side decreased the outward current. In both cases, the apparent pKa was voltage-dependent with apparent pKa at 0 mV = approximately 9.2. The channel may be blocked by OH(-) ions, or protons may titrate a site in the pore necessary for ion permeation. These data demonstrate that the permeation properties of Cl(Ca)Cs are different from those of CFTR or ClC-1, and provide insights into the nature of the Cl(Ca)C pore.
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PMID:Anion permeation in Ca(2+)-activated Cl(-) channels. 1109 50

High plasma homocysteine concentrations have been found to be associated with atherosclerosis and thrombosis of arteries and deep veins. The oxidative damage mediated by hydrogen peroxide production during the metal-catalyzed oxidation of homocysteine is to date considered to be one of the major pathophysiological mechanisms for this association. In this work, a very sensitive and accurate method was employed to measure the effective production of H2O2 during homocysteine oxidation. Furthermore, the interaction of homocysteine with powerful oxidizing species (hypochlorite, peroxynitrite, ferrylmyoglobin) was evaluated in order to ascertain the putative pro-oxidant role of homocysteine. Our findings indicate that homocysteine does not produce H2O2 in a significant amount (1/4000 mole/mole ratio of H2O2 to homocysteine). Moreover, homocysteine strongly inhibits the oxidation of luminol and dihydrorhodamine by hypochlorite or peroxynitrite and rapidly reduces back ferrylmyoglobin, the oxidizing species, to metmyoglobin. All these results should, in our opinion, lead to a rethinking of the commonly held view that homocysteine oxidation is one of the main causative mechanisms of cardiovascular damage.
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PMID:Is homocysteine a pro-oxidant? 1176 8

Polypyridyl complexes of Co decorated with 350-Da polyether chains (Co(350)(2+)) form molten phases of nucleic acids when paired with DNA counterions (Co(350)DNA) or 25-mer oligonucleotides. Analysis of voltammetry and chronoamperometry of mixtures of these phases with complexes having ClO(4)(-) counterions (Co(350)(ClO(4))(2)) and no other diluent provides charge transport rates from the oxidation and reduction currents for the complexes. As the mole fraction of the Co(350)(ClO(4))(2) complex in the mixture is varied from ca. 0.25 to 1, the physical diffusion constants derived from the Co(III/II) wave increase from 1 x 10(-11) cm(2)/s to 5 x 10(-10) cm(2)/s, and apparent diffusion constants dominated by the Co(II/I) electron self-exchange increase from 1 x 10(-10) cm(2)/s to 2 x 10(-8) cm(2)/s. Pure Co(350)DNA melts, containing no Co(350)(ClO(4))(2) complex, do not exhibit recognizable voltammetric waves; DNA suppresses the Co(II/I) electron transfer reactions of Co complexes for which it is the counterion. There are therefore two microscopically distinct kinds of Co(350) complexes, those with DNA and those with ClO(4)(-) counterions, with respect to their Co(II/I) electron-transfer dynamics, leading to percolative behavior in their mixtures. The electron-transfer rates of the Co(II/I) couple are controlled by the diffusive relaxation of the ionic atmosphere around the reaction pair, and the inactivity of the bound Co complexes can be attributed to the very low mobility of the anionic phosphate groups in the DNA counterion. Substitution of sulfonated polystyrene for DNA produced similar results, suggesting that this phenomenon is general to other polymer counterions of low mobility. We conclude that the measured Co(II/I) charge transport and electron-transfer rate constants reflect more the diffusive mobility of the perchlorate counterion than the intrinsic Co(II/I) electron hopping rate.
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PMID:Ion atmosphere relaxation and percolative electron transfer in Co bipyridine DNA molten salts. 1276 89

Two new angular trinuclear copper(II) complexes of formulation [Cu(3)(HL)LL'](ClO(4)), where L' is imidazole (Him, 1) or 1-methylimidazole (1-MeIm, 2) and H(3)L is a Schiff base obtained from the condensation of salicylaldehyde and 1,3-diaminopropan-2-ol (2:1 mole ratio), are prepared from a reaction of [Cu(2)L(mu-Br)] and [Cu(HL)] in the presence of L' and isolated as perchlorate salts. The crystal structures of 1 and 2 consist of a trinuclear copper(II) unit formed by the covalent linkage of monomeric type-2 mimic and dimeric type-3 mimic precursor complexes to give an angular arrangement of the metal atoms in the core which is a model for the active site structure of blue multicopper oxidases. In 1 and 2, the coordination geometry of two terminal copper atoms is distorted square-planar. The central copper has a distorted square-pyramidal (4 + 1) geometry. The mean Cu...Cu distance is approximately 3.3 A. The complex has a diphenoxo-bridged dicopper(II) unit with the phenoxo oxygen atoms showing a planar geometry. In addition, the complex has an endogenous alkoxo-bridged dicopper(II) unit showing a pyramidal geometry for the oxygen atom. The 1:1 electrolytic complexes show a d-d band at 607 nm. Cyclic voltammetry of the complexes in MeCN containing 0.1 M TBAP using a glassy carbon working electrode displays a Cu(3)(II)/Cu(2)(II)Cu(I) couple near -1.0 V (vs SCE). The variable temperature magnetic susceptibility measurements in the range 300-18 K show antiferromagnetic coupling in the complexes giving magnetic moments of approximately 3.0 mu(B) at 300 K and approximately 2.1 mu(B) at 18 K for the tricopper(II) unit. The experimental susceptibility data are theoretically fitted using a model with Heisenberg spin-(1)/(2) Hamiltonian for a trimer of spin-(1)/(2) copper(II) ions having two exchange parameters involving the alkoxo-bridged dicopper(II) (J1) and the diphenoxo-bridged dicopper(II) (J2) units, giving J1 and J2 values of -82.7, -73 cm(-1) for 1 and -98.3, -46.1 cm(-1) for 2, respectively. The structural features indicate a higher magnitude of anitiferromagnetic coupling in the alkoxo-bridged unit based on the greater value of the Cu-O-Cu angle in comparison to the diphenoxo-bridged unit. The core structures of 1 and 2 compare well with the first generation model complexes for the active site structure of multicopper oxidases in the oxidized form. The crystal structure of 1 exhibits a lamellar structure with a gap of approximately 7 A containing water molecules in the interlamellar space. Complex 2 forms a hexanuclear species due to intermolecular hydrogen bonding interactions involving two trimeric units. The crystal packing diagram of 2 displays formation of a three-dimensional framework with cavities containing the perchlorate anions.
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PMID:Covalent linkage of the type-2 and type-3 structural mimics to model the active site structure of multicopper oxidases: synthesis and magneto- structural properties of two angular trinuclear copper(II) complexes. 1295 Feb 15


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