Microcalorimetric titrations allow to recognize and investigate high-affinity ligand binding to Na,K-ATPase. Titrations with
the cardiac glycoside Ouabain, which acts as a specific inhibitor of the enzyme, have provided not only the thermodynamic
parameters of high-affinity binding with a stoichiometric coefficient of about 0.6 but also evidence for low-affinity binding
to the lipid. The marked enthalpic contribution of -95 kJ mol-1 at 298.2 K is partially compensated by a large negative entropy change, attributed to an increased interaction between water
and the protein. The calorimetric ADP and ATP titrations at 298.2 K are indicative of high-affinity nucleotide binding either
in 3 mM NaCl, 3 mM MgCl2 or at high ionic strength such as 120 mM choline chloride. However, no binding is detected in the buffer solution alone at
low ionic strength. The affinities for ADP and ATP are similar, around 106 M-1 and the stoichiometric coefficients are close to that of Ouabain binding. The exothermic binding of ADP is characterized
by a ΔH and ΔS value of -65 kJ mol-1 and -100 J mol-1 K-1, respectively. TheΔH value for ATP binding is larger than for ADP and is compensated by a larger, unfavorable ΔS value. This
leads to an enthalpy/entropy compensation, which could express that H-bond formation represents the major type of interaction.
As for Ouabain, the negative ΔS values that are also characteristic of nucleotide binding can indicate an increase of solvate
interaction with the protein due to a conformational transition occurring subsequent to the binding process. The resulting
binding constants are discussed with regard to the results of other studies employing different techniques. A molecular interaction
model for nucleotide binding is suggested.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
We investigate minimum vertex degree conditions for 3-uniform hypergraphs which ensure the existence of loose Hamilton cycles. A loose Hamilton cycle is a spanning cycle in which only consecutive edges intersect and these intersections consist of precisely one vertex. 相似文献
In the last decade, substantial research in the field of post‐plasma grafting surface modification has focussed on the introduction of carboxylic acids on surfaces by grafting acrylic acid (AAc). In the present work, we report on an alternative approach for biomaterial surface functionalisation. Thin poly‐ε‐caprolactone (PCL) films were subjected to a dielectric barrier discharge Ar‐plasma followed by the grafting of 2‐aminoethyl methacrylate (AEMA) under UV‐irradiation. X‐ray photoelectron spectroscopy (XPS) confirmed the presence of nitrogen. The ninhydrin assay demonstrated, both quantitatively and qualitatively, the presence of free amines on the surface. Confocal fluorescence microscopy (CFM), atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to visualise the grafted surfaces, indicating the presence of pAEMA. Static contact angle (SCA) measurements indicated a permanent increase in hydrophilicity. Furthermore, the AEMA grafted surfaces were applied for comparing the physisorption and covalent immobilisation of gelatin. CFM demonstrated that only the covalent immobilisation lead to a complete coverage of the surface. Those gelatin‐coated surfaces obtained were further coated using fibronectin. Osteosarcoma cells demonstrated better cell‐adhesion and cell‐viability on the modified surfaces, compared to the pure PCL films.
The present work reports on the synthesis and evaluation of a crosslinkable thiolated gelatin derivative. The effect of varying two parameters including the pH of the reaction buffer and the thiolating agent applied (i.e. N-acetylhomocysteine thiolactone versus Traut’s reagent) on the obtained modification degree was studied in a first part. The gelatin derivatives synthesized starting from N-acetylhomocysteine thiolactone and Traut’s reagent were characterized in depth using size exclusion chromatography and UV–VIS spectrophotometry. In a subsequent part of the present work, hydrogel films were prepared starting from the thiolated gelatin derivative developed using N-acetylhomocysteine thiolactone. The contributions of both the chemical and the physical crosslinking of the hydrogels developed were studied in depth using rheology, swelling experiments and texturometry. The results indicate that the physical structuring, inherent to gelatin, contributes to a large extent to the mechanical properties. However, the chemical crosslinking mostly determines the final hydrogel properties and can be controlled to a large extent. The gelatin-based gels are flexible, strong and transparent. A major advantage of disulfide-crosslinked hydrogels is the fact that the crosslinking is reversible. The latter could be interesting in view of future applications as cell carriers for tissue engineering. 相似文献
Polyepiiodohydrin was prepared from polyepichlorohydrin by the Finkelstein reaction with sodium iodide in butanone. An 88% degree of replacement of chlorine by iodine was obtained. The reaction of iodides with polyepichlorohydrin was accompanied by a substantial drop in molecular weight. The copolymer, which contains eight epiiodohydrin units per epichlorohydrin unit, has a glass transition temperature of 1°C and a density of 2.2 g/cm3. Properties of epiiodohydrin homopolymer were estimated by extrapolation of copolymer data. 相似文献