Action of palytoxin on apical H+/K+-ATPase in rat colon.
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Palytoxin stimulated a cation-dependent short-circuit current (Isc) in rat distal and proximal colon in a concentration-dependent fashion when applied to the mucosal surface of the tissue. The distal colon exhibited a higher sensitivity to the toxin. The palytoxin-induced Isc was blocked by vanadate but was resistant to ouabain or scilliroside, suggesting the conversion of a vanadate-sensitive H+/K+-ATPase into an electrogenic cation transporter. Cation substitution experiments with basolaterally depolarized tissues suggested an apparent permeability of the palytoxin-induced conductance of Na+>K+>Li+. Immunohistochemical control experiments confirmed the absence of the Na+/K+-ATPase in the apical membrane. Consequently, the pore-forming action of palytoxin is not restricted to Na+/K+-ATPase but is also observed with the colonic H+/K+-ATPase. (+info)
Effect of extracellular calcium, pH and borate on growth oscillations in Lilium formosanum pollen tubes.
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Calcium ions (Ca(2+)), protons (H(+)), and borate (B(OH)(4)(-)) are essential ions in the control of tip growth of pollen tubes. All three ions may interact with pectins, a major component of the expanding pollen tube cell wall. Ca(2+ )is thought to bind acidic residues, and cross-link adjacent pectin chains, thereby strengthening the cell wall. Protons are loosening agents; in pollen tube walls they may act through the enzyme pectin methylesterase (PME), and either reduce demethylation or stimulate hydrolysis of pectin. Finally, borate cross-links monomers of rhamnogalacturonan II (RG-II), and thus stiffens the cell wall. It is demonstrated here that changing the extracellular concentrations of Ca(2+), H(+) and borate affect not only the average growth rate of lily pollen tubes, but also influence the period of growth rate oscillations. The most dramatic effects are observed with increasing concentrations of Ca(2+) and borate, both of which markedly reduce the rate of growth of oscillating pollen tubes. Protons are less active, except at pH 7.0 where growth is inhibited. It is noteworthy, especially with borate, that the faster growing tubes exhibit the shorter periods of oscillation. The results are consistent with the idea that binding of Ca(2+) and borate to the cell wall may act at a similar level to alter the mechanical properties of the apical cell wall, with optimal concentrations being high enough to impart sufficient rigidity to the wall so as to prevent bursting in the face of cell turgor, but low enough to allow the wall to stretch quickly during periods of accelerating growth. (+info)
Chlorampenicol retention on, and penetration into, the rabbit eye.
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The retention of the antibiotic chloramphenicol on, and penetration into, the rabbit eye has been compared following administration in two vehicles. Samples were taken of both aqueous humor and a washing fluid applied to the conjunctival surface and the concentration of 14C-chloramphenicol determined. Greater tear film and aqueous humor drug concentrations, which are effective against many organisms, were found with a vehicle which enhanced retention time on the ocular surfaces. (+info)
Tensile properties of Arabidopsis cell walls depend on both a xyloglucan cross-linked microfibrillar network and rhamnogalacturonan II-borate complexes.
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The mechanical properties of plant organs depend upon anatomical structure, cell-cell adhesion, cell turgidity, and the mechanical properties of their cell walls. By testing the mechanical responses of Arabidopsis mutants, it is possible to deduce the contribution that polymers of the cell wall make to organ strength. We developed a method to measure the tensile parameters of the expanded regions of turgid or plasmolyzed dark-grown Arabidopsis hypocotyls and applied it to the fucose biosynthesis mutant mur1, the xyloglucan glycosyltransferase mutants mur2 and mur3, and the katanin mutant bot1. Hypocotyls from plants grown in the presence of increasing concentrations of dichlorobenzonitrile, an inhibitor of cellulose synthesis, were considerably weakened, indicating the validity of our approach. In order of decreasing strength, the hypocotyls of mur2 > bot1 and mur1 > mur3 were each found to have reduced strength and a proportionate reduction in modulus compared with wild type. The tensile properties of the hypocotyls and of the inflorescence stems of mur1 were rescued by growth in the presence of high concentrations of borate, which is known to cross-link the pectic component rhamnogalacturonan II. From comparison of the mechanical responses of mur2 and mur3, we deduce that galactose-containing side chains of xyloglucan make a major contribution to overall wall strength, whereas xyloglucan fucosylation plays a comparatively minor role. We conclude that borate-complexed rhamnogalacturonan II and galactosylated xyloglucan contribute to the tensile strength of cell walls. (+info)
Effect of sodium tetraborate (borax) on the thermal properties of frozen aqueous sugar and polyol solutions.
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The effect of sodium tetraborate (Na(2)B(4)O(7), borax) on the thermal property of frozen aqueous sugar and polyol solutions was studied through thermal analysis. Addition of borax raised the thermal transition temperature (glass transition temperature of maximally freeze-concentrated solutes; T(g)') of frozen sucrose solutions depending on the borax/sucrose concentration ratios. Changes in the T(g)' of frozen mono- and disaccharide solutions suggested various forms of complexes, including those of a borate ion and two saccharide molecules. Borax exerted the maximum effect to raise the oligosaccharide and dextran T(g)'s at borax/saccharide molar ratios of approximately 1-2 (maltose and maltooligosaccharides), 2 (dextran 1060), 5 (dextran 4900), and 10 (dextran 10200). Further addition of borax lowered T(g)'s of the saccharide solutions. Borax also raised T(g) and T(g)' temperatures of frozen aqueous glycerol solutions. The decreased solute mobility in frozen solutions by the borate-polyol complexes suggested higher collapse temperature in the freeze-drying process and improved stability of biological systems in frozen solutions. (+info)
Synthesis and conformation control of peptide ribonucleic acid containing 5'-amino-5'-deoxyribopurinenucleosides.
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A novel nucleic acid model, i.e. peptide ribonucleic acid (PRNA), tethering 5'-amino-5'-deoxypyrimidine ribonucleoside as a recognition site for nucleic acids, has been designed and synthesized. We have demonstrated that the recognition behavior of PRNA with complementary oligopurinenucleotides can be controlled externally through the orientational switching of the pyrimidine nucleobase of PRNA induced by added borates. We extend this methodology of controlling the nucleobase orientation and recognition behavior of novel mono and oligomeric PRNAs containing 5'-amino-5'-deoxypyrimidine and/or purinenucleosides. In case of the PRNA oligomer containing pyrimidine-purine mixed sequence, efficient orientational switching of nucleobases induced by added borates was also observed. (+info)
Rapid determination of 226Ra and uranium isotopes in solid samples by fusion with lithium metaborate and alpha spectrometry.
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A simple and rapid method has been developed to determine 226Ra in rocks, soils, and sediments. Samples are decomposed by fusion with lithium metaborate and the melt is dissolved in a solution containing sulfates and citric acid. During the dissolution, a fine suspension of mixed barium and radium sulfates is formed. The microcrystals are collected on a membrane filter (pore size 0.1 microm) and analysed in an alpha spectrometer. Application of a 133Ba tracer enables us to assess the loss of the analyte, which only rarely exceeds 10%. All analytical operations, beginning from sample decomposition to source preparation for alpha spectrometry, can be accomplished within 1 or 2 h. With uranium determination, the filtrate is spiked with a 232U tracer and passed through a column loaded with a Dowex AG (1 x 4) anion-exchange resin in the sulfate form. Interfering elements are eluted with dilute sulfuric acid followed by concentrated hydrochloric acid. Uranium is eluted with water, electrodeposited on silver discs, and analysed in the alpha spectrometer. The method was tested on reference soil and sediment materials and was found to be accurate within the estimated uncertainties. (+info)
REPRESSIBLE ACID PHOSPHOMONOESTERASE AND CONSTITUTIVE PYROPHOSPHATASE OF SACCHAROMYCES MELLIS.
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Weimberg, Ralph (Northern Regional Research Laboratory, Peoria, Ill.), and William L. Orton. Repressible acid phosphomonoesterase and constitutive pyrophosphatase of Saccharomyces mellis. J. Bacteriol. 86:805-813. 1963.-Saccharomyces mellis produces a nonspecific acid phosphomonoesterase (pH optimum of 5.5 to 6.0) when grown in a medium devoid of phosphate. Only minimal amounts of this enzyme are present in cells harvested from media containing phosphate. The enzyme requires no cofactors. It is inhibited by such anions as phosphate, arsenate, molybdate, and borate. S. mellis also contains an inorganic pyrophosphatase with a pH optimum of 7.5. The properties of this enzyme are distinctly different from those of the acid phosphomonoesterase. The pyrophosphatase requires Mg(++) for activity. This enzyme is constitutive, since it is present in cells regardless of the phosphate content of the growth medium. (+info)