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At least 991 records · Page 55Linked to original sources
PubMed2003

Defining metal ion inhibitor interactions with recombinant human H- and L-chain ferritins and site-directed variants: an isothermal titration calorimetry study.

Zinc and terbium, inhibitors of iron incorporation in the ferritins, have been used for many years as probes of structure-function relationships in these proteins. Isothermal titration calorimetric and kinetic measurements of Zn(II) and Tb(III) binding and inhibition of Fe(II) oxidation were used to identify and characterize thermodynamically ( n, K, Delta H degrees, Delta S degrees, and Delta G degrees ) the functionally important binding sites for these metal ions in recombinant human H-chain, L-chain, and H-chain site-directed variant ferritins. The data reveal at least two classes of binding sites for both Zn(II) and Tb(III) in human H-chain ferritin: one strong, corresponding to binding of one metal ion in each of the eight three-fold channels, and the other weak, involving binding at the ferroxidase and nucleation sites of the protein as well as at other weak unidentified binding sites. Zn(II) and Tb(III) binding to recombinant L-chain ferritin showed similar stoichiometries for the strong binding sites within the channels, but fewer weaker binding sites when compared to the H-chain protein. The kinetics and binding data indicate that the binding of Zn(II) and Tb(III) in the three-fold channels, which is the main pathway of iron(II) entry in ferritin, blocks the access of most of the iron to the ferroxidase sites on the interior of the protein, accounting for the strong inhibition by these metal ions of the oxidative deposition of iron in ferritin.

Apoferritins↗
PubMed1994

Appropriate interpretation of indirect calorimetry for determining energy expenditure of patients in intensive care units.

Energy expenditure varies with patient agitation. We asked whether energy expenditure determined from 5 minutes of measurement with less than 5% variation in minute-to-minute measurements (short mean) was similar to energy expenditure determined from a longer measurement period (long mean; average duration: 31 minutes). The difference between the short mean and the long mean was less than 5% for 42 of 47 patients in intensive care units; the difference was more than 10% for 2 patients. We also generated a statistical model simulating energy expenditure measurement variations of 5% to 20%, and calculated the necessary measurement durations required to achieve a 3% error in measurement. The statistical model showed that for energy expenditure variations of 5%, 10%, 15%, and 20%, the necessary durations of measurement to achieve a 3% error were 3, 9, 16, and 25 minutes, respectively. We conclude that energy expenditure may be determined using the mean of a 5-minute period of measurement if variation in that measurement is less than 5%. Larger variation requires longer periods of measurement.

Calorimetry, Indirect↗
PubMed1992

Two-dimensional differential scanning calorimetry: simultaneous resolution of intrinsic protein structural energetics and ligand binding interactions by global linkage analysis.

A general theoretical development for the design and analysis of two-dimensional thermal stability surfaces of proteins is presented. The surfaces are generated from multiple excess heat capacity profiles ( vs T) obtained at varying concentrations of an interacting ligand. The energetics of both the intrinsic protein stability and the protein-ligand interaction are simultaneously resolved by employing statistical thermodynamic models in global linkage analysis. This formalism allows resolution of the intrinsic protein folding-unfolding parameters (enthalpy, entropy, and heat capacity changes) as well as the ligand interaction parameters (binding stoichiometry, enthalpy, entropy, and heat capacity changes). The theory has been applied to the case of ribonuclease A and its interaction with cytidine-2'-monophosphate. The accuracy of the thermodynamic parameters obtained by this approach compares within error with those parameters that can be obtained by direct measurements.

Binding Sites↗
PubMed1985

Structural analyses of various Cu2+, Zn2+-superoxide dismutases by differential scanning calorimetry and Raman spectroscopy.

The thermal denaturation profile of the Cu2+, Zn2+ metalloenzyme, bovine superoxide dismutase, consists of two primary components, the major component denatures irreversibly at Tm = 104 degrees C with a total enthalpy (delta Hcal) of 7.30 cal/g. Reduction of Cu(II) to Cu(I) with potassium ferrocyanide lowers Tm to 96 degrees C and delta Hcal to 6.96 cal/g. The apo-form of bovine superoxide dismutase (both Cu and Zn removed) denatures at 60 degrees C with an enthalpy only one-half that of the holo-form. The reduced thermal stability, which indicates a greater ability to change conformation, may explain the previously observed much greater membrane binding of the apo-enzyme. Reconstitution with Zn2+, Cu2+, or Zn2+ and Cu2+ raises Tm to 80, 89, or 102 degrees C, respectively, with corresponding increases in the enthalpy. Thus, the metal ions considerably stabilize the enzyme and must somewhat affect conformation. The effect of Cu2+ alone is greater than that of Zn2+, although both are needed for full stability. Raman spectroscopy indicates little difference in secondary structure between the apo- and holo-forms, implying that the increased stability due to metal binding is not caused by an extreme structural reorganization. The value of Tm of canine and yeast superoxide dismutase is also lowered by reduction of Cu(II). The reduced form of the yeast enzyme denatures irreversibly, as do all forms of the bovine and canine enzymes, but the oxidized form is unique in that it denatures reversibly. Thus, the copper ion must be oxidized for renaturation and appears to act as a nucleation site.

Animals↗
PubMed1978

Differential scanning calorimetry of dipalmitoyl phosphatidylcholine analogues and of their interaction products with basic polypeptides.

The thermotropic behaviour of dipalmitoyl phosphatidylcholine analogues with a varying number (n) of CH2 groups between the phosphate and the quaternary ammonium has been investigated. The temperature (Tm) and the enthalpy (deltaH) of the phase transition are non-monotonous functions of the number of CH2 groups. Tm oscillates between 40 and 45 degrees C and deltaH between 7 and 13 kcal/mol for a variation of n between 2 and 11. It is concluded that the hydrocarbon chains in the head groups do not penetrate the hydrocarbon region and do not contribute directly to the melting of the acyl chains. It is suggested that their length may affect the critical balance between the attractive and the repulsive forces within the bidimensional lattice of the head groups. Copolypeptides of lysine with phenylalanine do not appreciably affect the Tm but have a pronounced effect on deltaH of the lipid phase transition, which depends strongly on the ratio of the two amino acids in the polypeptide. The effect of copolypeptide of any defined composition on deltaH is also a non-monotonous function of the number of CH2 groups in the phosphatidylcholine head group, but it does not parallel completely the oscilations in the Tm and deltaH of the pure lipids.

Calorimetry, Differential Scanning↗
PubMed1980

A differential scanning calorimetry study of the interaction of gangliosides with peanut lectin, serotonin and daunomycin.

Thermotropic behaviour of human Tay-Sachs ganglioside and of mixed bovine brain gangliosides, before and after interaction with peanut lectin, serotonin and daunomycin, was investigated. Interaction of mixed brain gangliosides with peanut lectin or serotonin causes a decrease in the enthalpy of melting, whereas interaction of this lectin with Tay-Sachs ganglioside does not influence the enthalpy of melting. Serotonin causes a small increase in the enthalpy of melting of the Tay-Sachs ganglioside.

Arachis↗
PubMed1989

Solubilization of DMPC and DPPC vesicles by detergents below their critical micellization concentration: high-sensitivity differential scanning calorimetry, Fourier transform infrared spectroscopy and freeze-fracture electron microscopy reveal two interaction sites of detergents in vesicles.

The interaction of sodium deoxycholate, sodium cholate and octyl glucoside with sonicated vesicles of L alpha-dimyristoyl-phosphatidylcholine (DMPC) and L alpha-dipalmitoylphosphatidylcholine (DPPC) at concentrations below the critical micellization concentration (cmc) of the detergents was studied by high-sensitivity DSC (hs-DSC), Fourier transform infrared spectroscopy (FT-IR) and freeze-fracture electron microscopy. The two phospholipids exhibited a striking different thermotropic behaviour in the presence of these detergents. For DPPC vesicles, the detergents were found to interact exclusively in the aqueous interface region of the bilayer below the membrane saturation concentration Rsat while in DMPC vesicles two coexisting interaction sites below this concentration persist. These are detergents which interact at the aqueous interface region (site 1) and in the acyl chain region (site 2) of the DMPC vesicles. The partition coefficients K of the detergents between DPPC vesicles and the water phase were calculated from the hs-DSC results at two detergent/phospholipid molar ratios Rtot less than or equal to Rsat as 0.35, 0.049 and 0.040 mol-1 for sodium deoxycholate, sodium cholate and octyl glucoside, respectively. In contrast, for DMPC the K values for Rtot less than or equal to Rsat were found to be dependent on Rtot due to the occupation of site 2 by the detergents above a certain Rtot. The model is discussed on the basis of the detergents free energies of transfer from the water phase to site 1 and site 2 of the vesicles, respectively. The solubilization behaviour of DPPC vesicles, dependent on whether the total detergent concentration is above or below the cmc at Rsat, differed significantly as revealed by hs-DSC. This suggests that in the latter case an additional hydrophobic effect could facilitate the formation of disc shaped mixed micelles. Moreover, this different behaviour was employed to measure the cmc values of the detergents studied in the presence of the vesicles by hs-DSC.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1996

Studies on the thermotropic effects of cannabinoids on phosphatidylcholine bilayers using differential scanning calorimetry and small angle X-ray diffraction.

We have studied the thermotropic properties of a wide variety of cannabinoids in DPPC bilayers. The molecules under study were divided into four classes: (a) classical cannabinoids possessing a phenolic hydroxyl group; (b) delta9-THC metabolites with an additional hydroxyl group on the C ring; (c) non-classical cannabinoids, and (d) cannabinoids with a protected phenolic hydroxyl group. The results showed that the first three groups have similar effects on the thermotropic properties of DPPC bilayers up to x = 0.05 (molar ratio) and that these effects do not parallel their biological activity. For concentrations less than x = 0.01, cannabinoids affect mainly the pretransition temperature in a progressive manner until its final abolishment. At x = 0.05, they further affect the main phase transition by lowering its phase transition temperature and broadening its half width. At high concentrations the thermograms have multiple components, indicating that membranes are no longer homogeneous but rather consist of different domains. At these concentrations cannabinoids with more hydroxyl groups give simpler thermograms. Low concentrations of cannabinoids in group d affect significantly the pretransition temperature, while high concentrations affect only marginally the main phase transition by slightly lowering its temperature and broadening its half width. These results point out the importance of the phenolic hydroxyl group in inducing membrane perturbations. The d-spacing data from our small angle X-ray diffraction experiments show that delta8-THC produces significant structural changes in the lipid bilayer, including the gel-phase tilting angle, the intermolecular cooperativity and the gauche:trans conformer ratio. Conversely, the inactive analog Me-delta8-THC does not cause drastic changes to the bilayer structure.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1976

Studies of the lipid binding characteristics of the apolipoproteins from human high density lipoprotein. II. Calorimetry of the binding of apo AI and apo AII with phospholipids.

The interactions of lysophosphatidylcholine and synthetic 1,2-dimyristoyl-sn-glycerophosphocholine (DMPC) liposomes with the isolated HDL-apolipoproteins, apo AI and apo AII, has been studied by microcalorimetry. Complex formation is a highly exothermal process characterized by a maximal enthalpy of about --200 kcal/mol of apoprotein when added to DMPC at 28 degrees C in 0.05 M sodium carbonate/bicarbonate buffer, pH 9.6. For the apo AI apoprotein, the binding consists of two processes, one endothermal occurring at low phospholipid/protein ratios and one exothermal predominant at higher phospholipid levels. The endothermal process has been attributed to a lipid-induced disaggregation of the apo AI while the exothermal process is similar to the binding of apo AII or apo HDL to phospholipids. The binding of a constant AI and apo AII, demonstrates the existence of a maximal association at a 1 : 1 molar ratio of the apolipoproteins. The sequential binding of DMPC to apo AI and apo AII suggests the existence of cooperativity between the two apoproteins in phospholipid binding as apo AII promotes the incorporation of apo AI into a protein-phospholipid complex.

Apoproteins↗