cAMP receptor protein from escherichia coli as a model of signal transduction in proteins--a review.

In Escherichia coli, cyclic AMP receptor protein (CRP) is known to regulate the transcription of about 100 genes. The signal to activate CRP is the binding of cyclic AMP. It has been suggested that binding of cAMP to CRP leads to a long-distance signal transduction from the N-terminal cAMP-binding domain to the C-terminal domain of the protein, which is responsible for interaction with specific sequences of DNA. The signal transduction plays a crucial role in the activation of the protein. The most sophisticated spectroscopic techniques, other techniques frequently used in structural biochemistry, and site-directed mutagenesis have been used to investigate the details of cAMP-mediated allosteric control over CRP conformation and activity as a transcription factor. The aim of this review is to summarize recent works and developments pertaining to cAMP-dependent CRP signal transduction in E. coli.

Gel-derived materials of a CaO-P(2)O(5)-SiO(2) system modified by boron, sodium, magnesium, aluminum, and fluorine compounds.

Bioactive glass-ceramic materials of the CaO-P(2)O(5)-SiO(2) system modified by adding boron, magnesium, sodium, fluorine, and aluminum were obtained using the sol-gel method. Gel-derived materials were produced in the pellet form obtained by compression of powders as well as in coatings on glass slides. The materials obtained were examined in vitro with regard to the ability of calcium phosphate layer to form on the material surface as the result of contact with simulated body fluid (SBF). SBF pH changes and calcium solubility in this solution were determined and scanning electron microscopy, energy-dispersive X-ray analysis, and infrared spectroscopy studies were conducted before and after contact of the materials with SBF. The gels modified by aluminum were amorphous, whereas the sodium and fluorine additives promoted the bulk crystallization of gel-derived materials. The ability of calcium phosphates to crystallize on the surface of gel-derived materials depended only slightly on the types of additives applied, and the character of this dependence was different from that observed in melted glasses. Moreover, to estimate the biocompatibility of gel-derived coatings, we examined the proliferation, collagen synthesis, adhesion, and morphology of fibroblasts (NRK cells) cultured in the presence of gel-derived materials. The results of these experiments showed that none of the tested materials significantly reduced any cell function.

Evaluation of biocompatibility of apatite-wollastonite ceramics in fibroblast cultures.

The aim of this work has been to test the biocompatibility of four bioactive, gel derived glass-ceramic materials of CaO-PO2-SiO2 system, modified by addition of boron, aluminum and magnesium compounds. We have examined the growth, collagen synthesis, adhesion and morphology of NRK rat fibroblasts cultured in direct and indirect contact with biomaterials. The growth of cells cultures has been quantified by two methods: [3H]thymidine incorporation and direct counting of cells. The level of collagen synthesis has been used as a parameter describing metabolic activity of cells. Cellular morphology has been assessed following 24 h and 4 days of culturing cells on biomaterials by using SEM and confocal microscopy, respectively. Additionally, in order to obtain information about the attachment of cells to substratum the presence of focal contacts has been examined. The results of all the experiments have demonstrated that none of the materials under study significantly altered cellular functions that were tested. This indicates that additions of MgO, Al2O3 and B2O3 have not induced cytotoxicity of the materials under study. This qualifies them for further in vivo experiments.