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At least 1,261 records · Page 70Linked to original sources
PubMed1997

Partitioning of octyl glucoside between octyl glucoside/phosphatidylcholine mixed aggregates and aqueous media as studied by isothermal titration calorimetry.

Stepwise dilution of lipid-surfactant mixed micelles first results in extraction of surfactant from the mixed micelles into the aqueous medium. Subsequently mixed micelles transform into vesicles, within a range of compositions that corresponds to equilibrium coexistence between these two types of aggregates. Further dilution results in extraction of surfactant from the resultant mixed vesicles. In the present study, we have investigated the heat evolution of these processes, as they occur in mixed systems composed of egg phosphatidylcholine (PC) and the nonionic surfactant octylglucoside (OG). A combined use of isothermal titration calorimetry (ITC) and photon correlation spectroscopy (PCS), capable of monitoring phase transformations, revealed that 1) The sum of all of the studied processes (i.e., extraction of OG from mixed micelles and vesicles and the phase transformation) is isocaloric at approximately 40 degrees C throughout the whole dilution. At lower temperatures, all of the dilution steps are exothermic, whereas at higher temperatures all of them are endothermic. 2) At all temperatures, the absolute value of the heat associated with each dilution step within the range of coexistence of micelles and vesicles is almost constant and larger than in either the micellar or the vesicular range. We give an interpretation of these calorimetric data in terms of the relationship between the composition of the mixed aggregates Re and the aqueous concentration of surfactant monomers Dw. Assuming that the main contribution to the heat evolution is due to extraction of surfactant from mixed aggregates to the aqueous solution, we deduce the relationship Dw(Re) characterizing the system over the whole range of compositions. We find that, in accord with thermodynamic expectations, Dw is almost constant throughout the range of coexistence of mixed micelles and vesicles.

Absorptiometry, Photon↗
PubMed1997

Titration calorimetry of anesthetic-protein interaction: negative enthalpy of binding and anesthetic potency.

Anesthetic potency increases at lower temperatures. In contrast, the transfer enthalpy of volatile anesthetics from water to macromolecules is usually positive. The transfer decreases at lower temperature. It was proposed that a few selective proteins bind volatile anesthetics with negative delta H, and these proteins are involved in signal transduction. There has been no report on direct estimation of binding delta H of anesthetics to proteins. This study used isothermal titration calorimetry to analyze chloroform binding to bovine serum albumin. The calorimetrically measured delta H cal was -10.37 kJ.mol-1. Thus the negative delta H of anesthetic binding is not limited to signal transduction proteins. The binding was saturable following Fermi-Dirac statistics and is characterized by the Langmuir adsorption isotherms, which is interfacial. The high-affinity association constant, K, was 2150 +/- 132 M-1 (KD = 0.47 mM) with the maximum binding number, Bmax = 3.7 +/- 0.2. The low-affinity K was 189 +/- 3.8 M-1 (KD = 5.29 mM), with a Bmax of 13.2 +/- 0.3. Anesthetic potency is a function of the activity of anesthetic molecules, not the concentration. Because the sign of delta H determines the temperature dependence of distribution of anesthetic molecules, it is irrelevant to the temperature dependence of anesthetic potency.

Anesthetics↗
PubMed2003

An enhancer-titration effect induces digit-specific regulatory alleles of the HoxD cluster.

Mice carrying transgenes targeted upstream the HoxD cluster display abnormal digits, with alterations resembling those obtained with loss of functions of Hoxd genes. Because the HoxD cluster remained entirely untouched by the insertional events, we investigated whether these phenotypes were induced by regulatory modifications at a distance. We report here that these targeted relocations behaved as hypomorphic alleles of the distantly located gene Hoxd13 and showed that posterior Hoxd genes located in cis with the integration site were down-regulated. Genetic analyses suggested that this down-regulation resulted from the titration of the activity of a remote located enhancer sequence. These results indicate that the transcriptional efficiency of Hoxd genes in digits could be modulated by the presence of other, unrelated, promoters, within the regulatory landscape of this enhancer. Modifications in these latter transcription units may thus impact upon digit morphology, through misregulation of Hoxd genes, thus illustrating the "buffering effect" that such a global regulatory element can exert upon a short genomic interval.

Animals↗
PubMed1999

TOP mRNAs are translationally inhibited by a titratable repressor in both wheat germ extract and reticulocyte lysate.

Vertebrate TOP mRNAs contain a 5' terminal oligopyrimidine tract (5' TOP), which is subject to selective translational repression in non-growing cells or in cell-free translation systems. In the present study, we monitored in vitro the effect of increasing amounts of a 16 nucleotides long oligoribonucleotide representing the 5' terminus of mouse ribosomal protein S16 mRNA on the translation of TOP and non-TOP mRNAs. Our results demonstrate that the wild-type sequence (but not its mutant counterparts) derepresses the translation of mRNAs containing 5' TOP motifs, but failed to stimulate the translation of non-TOP mRNAs, even if the latter differed only by a single nucleotide from their 5' TOP-containing counterparts. Similar results have been obtained with both wheat germ extract and rabbit reticulocyte lysate. It appears, therefore, that translational repression of TOP mRNAs is achieved in vitro by the accumulation of a titratable repressor rather than by the loss of an activator and that this repressor recognizes multiple TOP mRNAs with a diverse set of 5' TOP motifs.

Actins↗
PubMed1999

Nucleotide binding to creatine kinase: an isothermal titration microcalorimetry study.

We investigated the binding of ATP in the presence and absence of Mg(2+) to dimeric muscle creatine kinase (CK) by isothermal titration microcalorimetry as a function of pH and temperature. The thermodynamic parameters for these events show that (1) binding of nucleotide to the CK active site does not involve proton exchange with the buffer and (2) the active sites are the only nucleotide binding sites on CK. Interdependence of the active sites in the dimer could not be demonstrated. As CK undergoes major structural changes upon Mg-nucleotide binding, a thermodynamic cycle was employed to calculate the contributions of domain movements to the observed enthalpies.

Animals↗
PubMed1999

Active site titration of gramicidin S synthetase 2: evidence for misactivation and editing in non-ribosomal peptide biosynthesis.

The catalytic competence of gramicidin S synthetase 2 (GS2) was determined by following the kinetics of PP(i) generation using active site titration measurements with [gamma-(32)P]ATP. The initial 'burst' of product formation can be correlated to the generation of the aminoacyl adenylate:enzyme complexes at the four amino acid activation domains and the subsequent aminoacylation of carrier domains, followed by a slow linear turnover of substrate due to breakdown of the intermediate. Simultaneous activation of all four amino acid substrates at a saturating concentration displayed a consumption of 8.3 ATP/GS2. In the presence of single amino acids, a binding stoichiometry higher than the anticipated two ATP per active site was obtained, implying misactivation at non-cognate domains. Breakdown of acyladenylate intermediates reflects a possible corrective mechanism by which the enzyme controls the fidelity of product formation.

Adenosine Triphosphate↗
PubMed1985

Titrating the dose of bromocriptine when treating hyperprolactinemic infertile women.

We have shown that a smaller dose of bromocriptine is effective in lowering the PRL level to the normal range in some hyperprolactinemic women. Based on these findings, we recommend that when treating hyperprolactinemic women who desire conception, the dose of bromocriptine should be titrated according to the response of circulating PRL levels. This will minimize the dose, reduce cost, probably reduce side effects, and possibly avoid undesirable functional effects such as corpus luteum dysfunction.

Bromocriptine↗
PubMed2002

Quantitation of functionality of poly(methyl methacrylate) by liquid chromatography under critical conditions followed by evaporative light-scattering detection. Comparison with NMR and titration.

Atom transfer radical polymerisation (ATRP) is a versatile 'living' controlled polymerisation technique for the synthesis of well-defined architectures such as block copolymers, gradient copolymers, hyperbranched polymers and telechelic polymers. ATRP provides control over molecular mass and molecular mass distribution and is suitable for the polymerisation of a wide variety of monomers, including methyl methacrylate. A chromatographic method was developed for an endgroup-based separation of low-molecular-mass poly(methyl methacrylate) (PMMA), based on liquid chromatography under critical conditions. With this method the PMMA, irrespective of its low-molecular-mass, is separated according to endgroups (functionality) due to interactions of the polar endgroups with the non-modified silica based stationary phase. The different series were identified using on-line atmospheric pressure ionisation electrospray mass spectrometry and quantified by evaporative light scattering detection. These results were compared with those obtained by NMR and titration.

Atmospheric Pressure↗
PubMed2003

Hydrous ferric oxide: evaluation of Cd-HFO surface complexation models combining Cd(K) EXAFS data, potentiometric titration results, and surface site structures identified from mineralogical knowledge.

The surface properties of ferrihydrite were studied by combining wet chemical data, Cd(K) EXAFS data, and a surface structure and protonation model of the ferrihydrite surface. Acid-base titration experiments and Cd(II)-ferrihydrite sorption experiments were performed within 3<-log[H(+)]<10.5 and 0.5<[Cd(t)]<12 mM in 0.3 M NaClO(4) at 25 degrees C, where [Cd(t)] refers to total Cd concentration. Measurements at -5.5 triple bond Fe-OH(-1/2),logk((int))=-8.29, assuming the existence of a unique intrinsic microscopic constant, logk((int)), and consequently the existence of a single significant type of acid-base reactive functional groups. The surface structure model indicates that these groups are terminal water groups. The Cd(II) data were modeled assuming the existence of a single reactive site. The model fits the data set at low Cd(II) concentration and up to 50% surface coverage. At high coverage more Cd(II) ions than predicted are adsorbed, which is indicative of the existence of a second type of site of lower affinity. This agrees with the surface structure and protonation model developed, which indicates comparable concentrations of high- and low-affinity sites. The model further shows that for each class of low- and high-affinity sites there exists a variety of corresponding Cd surface complex structure, depending on the model crystal faces on which the complexes develop. Generally, high-affinity surface structures have surface coordinations of 3 and 4, as compared to 1 and 2 for low-affinity surface structures.

Journal Article↗
PubMed2003

Host factor titration by chromosomal R-loops as a mechanism for runaway plasmid replication in transcription termination-defective mutants of Escherichia coli.

Two Escherichia coli genes, rnhA and recG, encode products that disrupt R-loops by hydrolysis and unwinding, respectively. It is known that the propensity for R-loop formation in vivo is increased during growth at 21 degrees C. We have identified several links between rnhA, recG, and R-loop-dependent plasmid replication on the one hand, and genes rho and nusG involved in factor-dependent transcription termination on the other. A novel nusG-G146D mutation phenocopied a rho-A243E mutation in conferring global deficiency in transcription termination, and both mutants were killed at 21 degrees C following overexpression of rnhA(+). Mutant combinations rnhA-nusG or recG-rho were synthetically lethal at 21 degrees C, with the former being suppressed by recG(+) overexpression. rho and nusG mutants were killed following transformation with plasmids such as pACYC184 or pUC19 (which have R-loop replication intermediates) even at 30 degrees C or 37 degrees C, and the lethality was correlated with greatly increased content of supercoiled monomer species of these and other co-resident R-loop-dependent plasmids. Plasmid-mediated lethality in the mutants was suppressed by overexpression of rnhA(+) or recG(+). Two additional categories of trans-acting suppressors of the plasmid-mediated lethality were identified whose primary effects were, respectively, a reduction in plasmid copy number even in the wild-type strain, and a restoration of the proficiency of in vivo transcription termination in the nusG and rho mutant strains. The former category of suppressors included rom(+), and mutations in rpoB(Q513L), pcnB, and polA, whereas the latter included a mutation in rho (R221C) and several non-null mutations (E74K, L26P, and delta64-137) in the gene encoding the nucleoid protein H-NS. We propose that an increased occurrence of chromosomal R-loops in the rho and nusG mutants leads to titration of a cyloplasmic host factor(s) that negatively modulates the stability of plasmid R-loop replication intermediates and consequently to runaway plasmid replication.

Bacterial Proteins↗
PubMed1994

A dose titration, and an open 6-week efficacy and safety study of desmopressin tablets in the management of nocturnal enuresis.

The efficacy and safety of 6 weeks of treatment with desmopressin tablets at doses of 200 to 400 micrograms.at bedtime were investigated in 33 children with monosymptomatic nocturnal enuresis. During an initial 1 to 2-week dose titration period 22 patients (67%) became either completely dry or showed improvement, 7 (21%) showed no response and 4 (12%) dropped out of therapy. During tablet treatment 17 patients on 400 micrograms.and 5 on 200 micrograms.at bedtime increased the number of weekly dry nights from 2.0 +/- 1.6 (standard deviation) during a 2-week observation period to 5.2 +/- 1.9 (p < 0.001). During a subsequent 2-week period 40 micrograms.intranasal desmopressin showed a similar overall efficacy, with a mean of 5.4 +/- 1.6 dry nights per week. In addition, intranasal treatment was able to increase the number of dry nights in 2 of the 7 nonresponders to tablet treatment.

Administration, Intranasal↗
PubMed1989

Terodiline: a dose titrated, multicenter study of the treatment of idiopathic detrusor instability in women.

Idiopathic detrusor instability is a common cause of lower urinary tract symptoms at all ages and in both sexes. Treatment initially is conservative and often includes drug therapy. Terodiline has the theoretical advantage of being a drug with anticholinergic and calcium channel blocking effects. Theoretically, by using a drug with dual action the beneficial effect of reduced detrusor overactivity might occur at a dosage below that likely to lead to the troublesome side effects experienced by patients who take pure anticholinergic agents. A total of 70 female patients completed a study characterized by extremely strict inclusion criteria and a tight protocol. Other novel elements to the study were the extensive use of urinary diaries for symptom evaluation, standardized urodynamic studies agreed upon by the participating centers and the dose titration design of the trial. Terodiline has been demonstrated to be a safe, well tolerated and effective drug in the treatment of idiopathic detrusor instability. Drug treatment led to significant decreases in urinary frequency and incontinence episodes. Pre-micturition symptoms, such as urgency, were markedly reduced and the voided volume was significantly increased. Although there were consistent trends towards greater improvement in the urodynamic measurements, when the terodiline and placebo groups were compared these did not reach statistical significance, partly due to a large improvement in the placebo group. Nevertheless, terodiline has been shown to be a useful drug for conservative management of patients with detrusor instability.

Adult↗
PubMed2002

On-line titration of volatile fatty acids for the process control of anaerobic digestion plants.

The on-line titration of volatile fatty acids (VFA) was found to be a reliable method to measure the substrate (metabolite) concentration without the use of expensive analytical devices. A measurement cell was designed that ensures stable long-term operation, high throughputs and copes with both very low and very high VFA concentrations. Using synthetic textile wastewater, a recalibration of the pH probe was necessary only twice a week. A good reproducibility of the VFA concentrations was determined and standard deviations were below +/- 1% of the measured concentration. Changing salt concentrations of the wastewater in the range of 2.5-150 gl(-1) NaCl did not influence the determined VFA concentration significantly. The method was suitable to control the hydraulic retention time in an acidic phase reactor and to determine the acidification rates of wastewater compounds in batch experiments.

Bacteria, Anaerobic↗
PubMed1997

Determining surface areas of marine alga cells by acid-base titration method.

A new method for determining the surface area of living marine alga cells was described. The method uses acid-base titration to measure the surface acid/base amount on the surface of alga cells and uses the BET (Brunauer, Emmett, and Teller) equation to estimate the maximum surface acid/base amount, assuming that hydrous cell walls have carbohydrates or other structural compounds which can behave like surface Brönsted acid-base sites due to coordination of environmental H2O molecules. The method was applied to 18 diverse alga species (including 7 diatoms, 2 flagellates, 8 green algae and 1 red alga) maintained in seawater cultures. For the species examined, the surface areas of individual cells ranged from 2.8 x 10(-8) m2 for Nannochloropsis oculata to 690 x 10(-8) m2 for Dunaliella viridis, specific surface areas from 1,030 m2.g-1 for Dunaliella salina to 28,900 m2.g-1 for Pyramidomonas sp. Measurement accuracy was 15.2%. Preliminary studies show that the method may be more promising and accurate than light/electron microscopic measurements for coarse estimation of the surface area of living algae.

Cell Division↗
PubMed2006

Characterization of specific donor binding to alpha1,4-N-acetylhexosaminyltransferase EXTL2 using isothermal titration calorimetry.

Glycosyltransferases encompass one of the largest families of enzymes found in nature. Their principle function is to catalyze the transfer of activated donor-sugar molecules to various acceptor substrates. The molecular basis that governs this specific transfer reaction, such as how a given transferase determines donor-sugar specificity, remains to be elucidated. Human alpha1,4-N-acetylhexosaminyltransferase (EXTL2) transfers N-acetylglucosamine and N-acetylgalactosamine but does not transfer glucose or galactose. Isothermal titration calorimetry (ITC) is a powerful technique used to characterize various binding reactions, including both protein-ligand and protein-protein interactions. ITC provides the binding stoichiometry, affinity, and the thermodynamic parameters free energy (DeltaG), enthalpy (DeltaH), and entropy (DeltaS) of these binding interactions. This chapter describes our ITC study demonstrating the two-step mechanism that regulates the specific binding of N-acetylhexosamines to EXTL2.

Acetylglucosamine↗
PubMed1998

Tight ligand binding affinities determined from thermodynamic linkage to temperature by titration calorimetry.

A general isothermal titration calorimetry method is described that can be used to determine equilibrium binding constants for high-affinity interactions of ligands with biological macromolecules. The method exploits the thermodynamic linkage between the ligand binding equilibrium constant and temperature. By measuring the binding enthalpy change for an interaction as a function of temperature directly, the change in affinity can be calculated with an integrated form of the van't Hoff equation that is applicable to ligand binding to biological macromolecules. When the temperature dependence of the affinity is combined with the absolute affinity determined independently at a convenient temperature (where the affinity can most accurately or most easily be measured), the absolute binding affinity over the entire temperature range is determined.

Antibodies, Monoclonal↗
PubMed1984

The titration of tetanus antitoxin I. Factors affecting the sensitivity of the indirect haemagglutination test.

Various factors affecting the indirect HA test for the titration of tetanus antitoxin have been evaluated with a view to obtaining maximum sensitivity in tests using unfixed sheep erythrocytes and sheep erythrocytes fixed with glutaraldehyde, formaldehyde and pyruvic aldehyde. The optimal concentration of tannic acid has been found to be 1/40 000 for tanning both fixed and unfixed sheep erythrocytes. Tanned sheep erythrocytes sensitized with 50 Lf/ml of tetanus toxoid at pH 7.2 for one hour were the most sensitive. Although the optimal temperature of sensitization was found to be 56 degrees C, unfixed cells tended to clump and lyse at this temperature. Thus a temperature of 37 degrees C was used to sensitize unfixed sheep erythrocytes. Sheep erythrocytes from different animals and the final concentration of sensitized sheep erythrocytes both had great effects on sensitivity. A final concentration of 0.5% of sensitized sheep erythrocytes was found suitable as a compromise between sensitivity and readability. The loss of sensitivity of fixed and sensitized erythrocytes was investigated by storing these cells at 4-8 degrees C for six to nine months.

Animals↗