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At least 19 recordsLinked to original sources

PubMed1976

The interaction of borate and sulfite with pyridine nucleotides.

The kinetics and equilibria of the borate interaction at ribose with NAD+ and NMN+ have been measured using as a chromophoric probe the perturbation effect borate has on the addition of sulfite to the 4 position of the nicotinamide ring. NAD+ and NMN+ have more favorable borate association constants than do their corresponding sulfite addition complexes. The rate of interaction of the ribose moiety with borate at low borate buffer concentration is dependent on the concentration of both borate and boric acid. At high borate concentration the rate becomes independent of borate concentration, indicating the existence of a two-step process for the interaction of NAD-sulfite with borate with a change of rate-determining step from the interaction of the ribose hydroxyl group with borate at low borate to an elimination of sulfite at high borate concentration. A linear free energy relationship with a slope of 0.94 describes an increased reactivity of the nucleotide for sulfite as the affinity of the nucleotide for sulfite increases.

Binding Sites↗

PubMed1976

Antifreeze glycoproteins from Antarctic fish. Inactivation by borate.

Antifreeze glycoprotein, which has previously been shown to be inactive in the presence of borate, migrates electrophoretically as the borate complex, presumably through formation of borate complexes with hydroxyl groups on the sugar side chains. Antifreeze glycoprotein (5 mg/ml) has been found to be completely active in the presence of 0.1 M borate at pH 7, but inactive at pH 9. A titration curve of pH versus the antifreeze activity of glycoprotein (5 mg/ml) in 0.1 M borate showed a progressive decrease in antifreeze activity as the pH was increased. Concomitant with decreases in activity were increases in binding of borate. At pH 9.0, nearly 2 mol of borate were complexed per glycotripeptide. Ultracentrifuge analyses showed similar molecular weights and laser quasi-elastic light scattering showed similar diffusions at pH 7.0 and 9.0 in borate and in the absence of borate. The binding of borate, rather than a change in conformation, is thus directly related to the loss of antifreeze activity. Alkaline borate also decreased hemagglutinating activity of Osage orange lectin and decreased the inhibition of the activity by the antifreeze glycoproteins.

Aldehydes↗

PubMed1976

Borate inhibition of yeast alcohol dehydrogenase.

Yeast alcohol dehydrogenase is inhibited competitively by borate with respect to NAD+. An unusual mechanism of competitive inhibition prevails: the competition for the substrate NAD+ by borate and enzyme. The following evidence supports this conclusion. (1) Much greater inhibition is observed with respect to NAD+ as compared with NADH as substrates. (2) Borate decreases the equilibrium constant of the overall reaction in the direction of ethanol oxidation, therefore, borate enters directly into the overall reaction rather than merely decreases the effectiveness of the catalyst. (3) The Ki values for unrelated enzyme reactions are identical for NAD+. (4) Stopped-flow experiments show burst kinetics only when NAD+ and borate are not premixed. (5) The Ki value is identical with the inverse of the borate-NAD+ complexation constant. (6) The pH dependence of the inhibitor demonstrates that only the B(OH)4-species is inhibiting. These results are consistent with the preferable binding of borate to NAD+ as compared with NADH. These two binding constants were found to be equal to 2000 +/- 60 and 130 +/- 8 M-1, respectively. In contrast to the liver enzyme, the yeast enzyme does not show pre-steady-state burst reactions in the reduction of NAD+. This would indicate that the interconversion of ternary complexes is at least partially rate limiting for the yeast enzyme.

Alcohol Oxidoreductases↗

PubMed1977

Effect of borate on the catalytic activities of muscle glyceraldehyde-3-phosphate dehydrogenase.

The effect of borate on glyceraldehyde-3-phosphate dehydrogenase from human, pig and rabbit muscle was studied. At lower concentration of borate only the dehydrogenase activity is inhibited, reversibly and competitively against NAD. At concentration of borate above 6 mM the plots of 1/v versus borate concentration become nonlinear and the inhibition is extended to the esterase and acetylphosphatase activities. In certain conditions a time-dependent inactivation and reactivation was observed. The direct interaction between borate (if present at concentration of at least 6 mM) and glyceraldehyde-3-phosphate dehydrogenase is postulated, the possible site of the reaction being the histidine residue(s). The esterase activity of the human muscle enzyme and the effect of borate on it are different from the other mammalian enzymes.

Animals↗

PubMed1978

Serine-borate complex as a transition-state inhibitor of gamma-glutamyl transpeptidase.

gamma-Glutamyl transpeptidase, a membrane-bound enzyme, functions in the gamma-glutamyl cycle to catalyze utilization of glutathione. It has been postulated that the amino-acid-stimulated utilization of glutathione by gamma-glutamyl transpeptidase reflects an aspect of amino acid translocation. As one approach to the effective in vivo inhibition of this enzyme, the inhibition of the enzyme by L-serine in the presence of borate buffers [Revel, J.P. & Ball, E.G. (1959) J. Biol. Chem. 234, 577-582] was reinvestigated. Inhibition by L-serine, D-serine, and alpha-methyl-DL-serine in the presence of borate is competitive with respect to gamma-glutamyl substrate and such inhibition is parallel to the activity of transpeptidase toward L-gamma-glutamyl, D-gamma-glutamyl, and L-gamma-(alpha-methyl)glutamyl derivatives. L-Serine and borate effectively protect against inactivation of the enzyme by the gamma-glutamyl analogs, 6-diazo-5-oxonorleucine and azaserine, which bind to the gamma-glutamyl site of the enzyme. These studies, kinetic investigations, equilibrium dialysis experiments, and other data support the view that inhibition is produced by formation of serine-borate complex which binds at the gamma-glutamyl binding site of the light subunit of gamma-glutamyl transpeptidase. The data indicate that serine-borate complex is a transition state inhibitor of gamma-glutamyl transpeptidase.

Azaserine↗

PubMed1977

Borate and glycerol inhibition of the aggregation of guinea pig platelets by bovine factor VIII and ristocetin.

To demonstrate the importance of the carbohydrate portions of bovine factor VIII and ristocetin for the induction of platelet aggregation, guinea pig platelets were treated with either borate or glycerol before and after addition of ristocetin or bovine factor VIII. Both borate and glycerol were capable of inhibiting the aggregation of blood platelets induced by adding bovine factor VIII or ristocetin to platelet-rich plasma. Furthermore, aggregates formed after treatment with either agent could be dispersed by high concentrations of either borate or glycerol. These effects did not appear to be solely the result of high ionic strength or of irreversible damage to the platelets. The results obtained support the hypothesis that the binding of the carbohydrate groups of factor VIII plays an important role in the induction of platelet aggregation and in the maintenance of aggregates formed in response to the treatment of platelet-rich plasma with bovine factor VIII or ristocetin.

Animals↗

PubMed1976

Hybridization of glyceraldehyde-3-phosphate dehydrogenase in borate.

Conditions for the hybridization of glyceraldehyde-3-phosphate dehydrogenase (GPD) [EC 1.2.1.12] in the presence of dilute borate were examined with horseshoe crab and rabbit GPDs. Hybridization was strongly dependent upon pH, borate concentration, and temperature. The optimum medium for hybridization was 10mM Tris-HCl-1 mM 2-mercaptoethanol-1mM EDTA containing 10-20 mM borate, pH 8.5-9.0. Hybridization was performed by incubation of two electrophoretically distinct GPDs at 30 degrees for 3-15 hr in the above medium at a protein concentration of 1-2 mg/ml. The time course of hybridization was analyzed under the optimized conditions. Symmetrical A2B2-type hybrid appeared only 5 min after incubation for 1 hr. Hybridization of GPDs from 7 different species was examined under the optimal conditions. Hybridization was detected with rabbit-horseshoe crab, yeast-rabbit, yeast-chicken, and chicken-horseshoe crab combinations. Subunit-subunit interaction, the mechanism of hybridization, and the structure of GPD are discussed based on the results obtained.

Animals↗

PubMed1976

The influence of borate and calcium on the gel formation of a sulfated polysaccharide from Ulva lactuca.

The water-soluble, sulfated polysaccharide isolated from Ulva lactuca, forms a soft gel when dialysed against sea-water, provided the polysaccharide concentration is 1% or higher and the pH above 7.5. The components of sea-water needed for this gel formation are boric acid and calcium ions. At concentration normally found in sea-water, neither borate nor calcium ions alone produce a gel. It is assumed that the gel formation involves the formation of borate-polysaccharide complexes leading to intermolecular linkages which are stabilized by calcium ions in an unknown manner. This assumption is supported by experiments with extraction of this polysaccharide from the dry seaweed and by the results obtained with the isolated polysaccharide. Agreement between these experiments leads to the conclusion that the sulfated polysaccharide (in vivo) most probably occurs as a gel stabilized by the borate and calcium ions in sea-water.

Borates↗

PubMed1976

The use of sodium borate impregnated silica gel plates for the separation of 3-0-methyl catecholamines from their corresponding catecholamines.

The use of sodium borate impregnated silica gel plates for the chromatographic separation of the catecholamines noradrenaline, adrenaline, and isoprenaline from their respective 3-0-methylated derivatives, normetanephrine, metanephrine, and methoxy-isoprenaline, is described. The parent catecholamines remain at the origin of the plates while the 3-0-methylated derivatives concentrate in discrete bands at the upper edge of the borate impregnated area (the "borate front").

Catecholamines↗

PubMed1976

[Practical use of lithium borate in thermoluminescent dosimetry (author's transl)].

The authors recall the functional principles of thermoluminescent dosimeters: heating, apparatus for measuring the emitted light, circulation of nitrogen, reference source. They take this opportunity to stress the essential role played by the circulation of nitrogen over the dosimeters which equilibrates the temperature of the photo multiplier, reduces the emission of unwanted light, prevents the combustion of dust or other possible impurities and finally improves the reproductibility of the measurements even for high dosod for finding the optimum working conditions for the heating apparatus of the planchette in the most simple T.L.D. readers and in those where the heating apparatus of the planchette has a pre-heating phase. They then study the dosimetric properties of lithium borate incorporated in thin teflon discs (type DLB. 0.13 and 0.4). This shows itself to be very interesting for certain uses because it is a solid dosimeter which does not require annealing between two measurements. The reproductibility of the measurements obtained with this material, the stability of its response relative to the delay between radiation and reading (fading), its response relative to the absorbed dose plus the nature and the energy of the rays, are presented with the usual reservations made for this type of dosimetry. The authors conclude by citing a few applications where they have been able to achieve a satisfactory result with the aid of lithium borate.

Borates↗

PubMed1978

Studies on the mode of action of phenylmercuric borate on Escherichia coli. I. Structural localization and kinetics of incorporation.

Phenylmercuric borate (PHB) is very rapidly incorporated into the cells of Escherichia coli, and binds directly to its sites of fixation. The rapid incorporation of PHB probably results from the lipophilic character of the [phenylmercuric]+ cation. The distribution of PHB in the cell is fairly uniform if one compares with that of the proteins. This shows the low specificity of PHB with regard to proteins, all of which appear to be potential sites for fixation. However, from the structural point of view, PHB is more differentiated in its distribution. The cell wall of E. coli and the soluble cytoplasmic fraction do not constitute important sites of fixation. On the contrary, the cytoplasmic membrane appears to be a preferential site of fixation. Moreover, it is very probable that the distribution of PHB in vivo should be even more likely at the cytoplasmic membrane since the process of homogenization of the cells solubilizes a large part of the proteins associated to the membrane. On the membrane, an important part of PHB seems to be associated with the ribosomes and particularly to the ribosomal proteins.

Bacterial Proteins↗

PubMed1978

Studies on the mode of action of phenylmercuric borate on Escherichia coli. II. Biochemical localization and inhibition of some metabolic activities.

The biochemical localization of phenylmercuric borate (PHB) on Escherichia coli shows that this disinfectant associates essentially with proteins. Protein electrophoresis demonstrates that each protein contains PHB, and that SH groups play a very important role in its fixation. The quantity of PHB able to associate with proteins is so large that many other electron donor groups must react with it. Moreover, it appears that concentration of PHB on cytoplasmic membrane results rather from the privileged position of this structure than from special physicochemical properties. The great reactivity of PHB towards proteins leads to numerous inhibitions and confers upon this antibacterial drug a very complex mode of action. Four important metabolic activities have been tested in the presence of PHB, namely: respiration, protein-synthesis, RNA synthesis and DNA synthesis. These four metabolic functions are rapidly and totally inhibited at low concentrations of PHB. The complexity of the mode of action of PHB makes the adaptation of bacteria to this disinfectant more difficult. In addition, in the case of plasmid dependent resistence, PHB, with its complexe mode of action, does not favour such a selection in opposition to the antibiotics which generally have a more specific mode of action.

Bacterial Proteins↗

PubMed1976

An assessment of lithium borate thermoluminescent dosimeters for the measurement of doses to patients in diagnostic radiology.

A pilot survey of doses to patients undergoing four types of radiological procedure--barium enemas, intravenous pyelography, cardiac catheterization and mammography--has been made using lithium borate TL dosimeters. The survey was designed to test the operational suitability of the dosimetry system and to gain experience and gather data for the planning of further larger surveys. The TL dosimeters were calibrated against conventional ionization chambers, and then used on patients for determining gonad doses and maximum doses to the skin. Few difficulties were encountered in using the system. The measured doses to patients have been compared with previous determinations by other authors and reasonable agreement demonstrated.

Adolescent↗

PubMed1976

Regulation of glutaminase B in Escherichia coli. II. Modulaltion of activity by carbosylate and borate ions.

Glutaminase B is both activated and inhibited by L-glutamate, the product of the reaction. The activation process is time- and temperature-dependent. Activation by L-glutamate alters the Vmax, So.5, and shape of the substrate saturation curve. The activation decays as a first order process with time after separation of L-glutamate from glutaminase B. L-Glutamate inhibits both glutaminase B and the glutamate-activated enzyme. Like L-glutamate, borate activates and inhibits glutaminase B. Inhibition of the enzyme by glutamine and glutamate analogs is also examined and similarities between the glutamate activation and activation by warming at 23 degrees are noted.

Adenosine Triphosphate↗

PubMed1975