SEARCH · Search PubMed
Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
The development of a photoacoustic calorimeter with a time resolution of 10 ns is presented, and the dynamics of the enthalpy and volume changes found in the photodissociation of CO from horse carboxymyoglobin are examined. With this enhanced time resolution a new transient species, the lifetime of which is 29 ns at 20 degrees C, is observed in the ligand dissociation process.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Thermal properties of azidohetarenes without reactive ortho-substituents, obtained by DSC analysis, were compared with the DSC data of ortho-phenyl and ortho-acyl substituted azidohetarenes, which give ring closure reactions either to indoles or to five-membered heterocycles such as isoxazoles. The reaction temperatures and reaction enthalpies give both information to prepare the reaction conditions and important safety information and were, in addition, used to find out relations between the temperatures or enthalpies with the three different reaction mechanisms.
Glycosylation of the Fc region of IgG (IgG-Fc) is essential for the full expression of Fc effector functions. The profound differences in functional activity observed between glycosylated and aglycosylated IgG have not previously been paralleled by the demonstration of large-scale structural changes. In the present study differential scanning microcalorimetry (DSMC) was used to investigate IgG-Fc glycoprotein stability and to determine the thermodynamic parameters for thermal unfolding, which will include a contribution from the intra-molecular oligosaccharide-protein interactions. The thermogram obtained for glycosylated IgG1-Fc yielded two clearly defined transitions whilst the glycosylated IgG4-Fc exhibited a single transition. The methodology was also able to reveal measurable differences in the stability of IgG4-Fc glycoforms differing by the presence or absence of terminal galactose residues; deglycosylated IgG4-Fc exhibited two transitions with evidence for destabilisation of the C(H)2 domain.
Thermal unfolding parameters were determined for a two-domain tetrameric enzyme, phosphorylating D-glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and for its isolated NAD(+)-binding domain. At pH 8.0, the transition temperatures (t(max)) for the apoforms of the native Bacillus stearothermophilus GAPDH and the isolated domain were 78.3 degrees C and 61.9 degrees C, with calorimetric enthalpies (DeltaH(cal)) of 4415 and 437 kJ/mol (or 30.7 and 22.1 J/g), respectively. In the presence of nearly saturating NAD(+) concentrations, the t(max) and the DeltaH(cal) increased by 13.6 degrees C and by 2365 kJ/mol, respectively, for the native apoenzyme, and by 2.8 degrees C and 109 kJ/mol for the isolated domain. These results indicate that interdomain interactions are essential for NAD(+) to produce its stabilizing effect on the structure of the native enzyme. The thermal stability of the isolated NAD(+)-binding domain increased considerably upon transition from pH 6.0 to 8.0. By contrast, native GAPDH exhibited greater stability at pH 6.0; similar pH-dependencies of thermal stability were displayed by GAPDHs isolated from rabbit muscle and Escherichia coli. The binding of NAD(+) to rabbit muscle apoenzyme increased t(max) and DeltaH(cal) and diminished the widths of the DSC curves; the effect was found to grow progressively with increasing coenzyme concentrations. Alkylation of the essential Cys149 with iodoacetamide destabilized the apoenzyme and altered the effect of NAD(+). Replacement of Cys149 by Ser or by Ala in the B. stearothermophilus GAPDH produced some stabilization, the effect of added NAD(+) being basically similar to that observed with the wild-type enzyme. These data indicate that neither the ion pairing between Cys149 and His176 nor the charge transfer interaction between Cys149 and NAD(+) make any significant contribution to the stabilization of the enzyme's native tertiary structure and the accomplishment of NAD(+)-induced conformational changes. The H176N mutant exhibited dramatically lower heat stability, as reflected in the values of both DeltaH(cal) and t(max). Interestingly, NAD(+) binding resulted in much wider heat capacity curves, suggesting diminished cooperativity of the unfolding transition.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
A comparison of the absorbed dose to tissue determined by various ionization chambers, Faraday cups, and an A-150 plastic calorimeter was performed in the 200 MeV proton beam of Orsay, France. Four European proton-therapy centers (Clatterbridge, UK, Louvain la Neuve, Belgium, and Nice and Orsay, France) participated in the comparison. An agreement of better than 1% was observed in the absorbed dose to A-150 measured with the different chambers of the participating groups. The mean ratio of the absorbed dose to A-150 determined with the calorimeter to that determined by the different ionization chambers in the different irradiation conditions was found to be 0.952 +/- 0.007 [1 standard deviation (SD)] according to the code of practice used by all the participating centers, based on Janni's tables of stopping powers and a value of 35.2 J/Coulomb for (W(air)/e)p. A better agreement in the mean ratio calorimeter/chamber, 0.985 +/- 0.007 (1 SD) is observed when using the proton stopping power ratio values recently published by the International Commission on Radiation Units and Measurements in Report no. 49. The mean ratio of these doses determined in accordance with the American Association of Physicists in Medicine protocol and using the new recommended stopping power tables becomes 1.002 +/- 0.007 (1 SD). Two Faraday cups agree in measured charge to within 0.8%; however, the calculation of dose is underestimated by up to 17%; compared with ion chamber measurements and seems to be very sensitive to measurement conditions, particularly to the distance to the collimator.
Microcalorimetry was used to characterise bicarbonate after treatment at high temperatures. By measuring the heat flow from a sample of bicarbonate at 100% relative humidity, the net exothermic contribution could be used to estimate the fraction of pyrolytically formed Na(2)CO(3). The enthalpy value corresponding to the heat of solution of Na(2)CO(3) was also applicable to a physical mixture of NaHCO(3)/Na(2)CO(3). However, from the characteristic peaks of the heat flow versus time curve, pyrolytically formed Na(2)CO(3) could be distinguished from that present in the physical mixture. The different bicarbonate batches of varying degree of pyrolytic decarboxylation were also observed at an elevated relative humidity of 54%. From these measurements it could be inferred that a decarboxylation of up to 4.5% could be allowed without any significant effect on the stability of bicarbonate at 54%.
Explore the source record for details and available documents.