In a previous paper, we reported on the structural propertics of a 35-residue pcptide corresponding to a modified basic subdomain (bSD) of the basic zipper protein u-Jun (residues 252-281 ) as deterrnincd by combined use of 'H-NMR, circular dichroisrn (CD) and Fourier transform infrared ( F T I R ) spectroscopies [Krcbs, D., Dahmani, B., El Antri, S., Monnot, M., Convert, O., Mauffret, O., Troalen, 1;. 8r Fcrmandjian, S. (1995) Eur: J. Binchem. 231, 370-3801. The fragmenls N P anci CP (the N-terminitl rcsidues 1-19 and C-terminal residues 16-35 of bSD, rcspectivcly) proved to be particularly useful for the assignment of the 'H-NMR spectra of the full-length bSD, which has bccn achievcd coniplctely in aqueous solution and partially in tritluoroethanol. Here, we report on lhc structural properties of NP and CP in aqueous solution and under varying H,O/tritluoroethanol conditions, again using 'H-NMK, C' D and FT-IR experiments. Both CD and FT-TR rcsults establishcd thal the fragments are weakly structured i n aqueous solution. Addition of trifluoroethanol to aqueous solutions of the peptidcs prciduced their stabilization into helix, following a profile sigmoidal for N P and nearly linear for CP. Quantitative NOES, secondary Ha chemical shifts, NH temperature coefficients and coupling conslants for thc peplidcs in aqueous solutions provided indications for weak hclix features (nuscent helices) manifested within two sites (continuous dNN NOES) in both NP and CP. For each peptide, an excellent agrcemen( was observed between experiments and predictions with the AGADIR program fur the location of these nuscent helices in the sequences. Trifluoroethanol provoked both the a-helix stabilization within these sitcs anci the cxhelix propagation to adjacent amino acid residues.Finally, our results reflected the high flexibility and hclix potential of the NP and CP fragments, thesc two propertics seeming crucial for the accomodation of c-J~iti to its specific DNA targets. The rcsults dzinonstrated also the fragmentation's benefits in dissecting a protein or a complex peptide into smaller fragments and analyzing their structure individually.
Matrix hybrid membranes, based on polyvinylidene fluoride (PVDF), poly (N-vinylpyrrolidone) (PVP), silica gel (SG) and zinc oxide (ZnO) were synthesized by phase inversion via immersion precipitation method. The characterization of membrane samples was performed using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), optical microscopy, contact angle, porosity, mean pore size and water permeability measurements. The FTIR analysis showed the appearance of new bands attributed to the functional groups of SG and ZnO. The XRD analysis confirmed a modification in the structure of membranes. The prepared membranes were used for the removal of hexavalent chromium (Cr(VI)) from aqueous solution. Membrane filtration experiments show that the water permeability and Cr(VI) rejection ratios increase with increasing the weight ratio ZnO (%)/SG (%). The maximum values of the Cr(VI) rejection rate and water permeability were respectively 85% and 685 L/m2hbar for weight ratios (0.75% of ZnO/0.25% of SG).
The structural properties of the basic subdomain of the basic zipper (bZIP) protein c-Jun were examined by joint means of 1H-NMR, CD and Fourier-transform infrared (FTIR) spectroscopies. The basic subdomain (residues 252-281 in c-Jun) is responsible for sequence-specific recognition of DNA. A modified basic subdomain bSD (residues 1-35) and its N-terminal part and C-terminal part fragments (NP, residues 1-19; and, CP, residues 16-35) were prepared by solid-phase synthesis and purified by HPLC. In aqueous solution, in the absence of DNA, bSD behaved mostly as an unstructured peptide characterized by only 5% alpha helix. However, upon mixing bSD and a specific DNA fragment, i.e. a CRE(cAMP-responsive element)-containing hexadecanucleotide, the alpha helix was stabilized to an extent of 20% at 20 degrees C or 35% at 2 degrees C. At the same time, no significant change could be detected in the DNA spectra. Addition of trifluoroethanol to an aqueous bSD sample resulted in an increase of the alpha-helix content so that about 60% of alpha helix was found at a ratio of 75% trifluoroethanol (20 degrees C). These effects were reflected in both CD and FTIR measurements. Changes shown by the CD spectra during the process suggested a mechanism dominated by a two-state helix/unordered transition. NMR data, namely alpha H chemical shifts, NOE cross-peaks and NH temperature coefficients provided indications for extended or nascent helix structures within four short stretches dispersed along the sequence for c-Jun bSD, contrasting with the unique and continuous stretch reported for Gcn4 (yeast general control protein 4) bSD in aqueous solution. Trifluoroethanol stabilized the alpha-helix structure mainly at these four sites. The malleability of the basic subdomain of c-Jun was emphasized in relation to its ability to fit the DNA helix in adopting an alpha-helix structure. The complex formation apparently requires substantial conformational change from the peptide and only little from the oligonucleotide.
The aim of this work to calculate the counting efficiency of NaI(Tl) 2 × 2 well-shaped scintillation detector (Canberra Inc.). The advantage of this type detector its high efficiency which used to determination the low level of radiation as natural occurring radioactive material (NORM). The gamma attenuation coefficients of natural radioisotopes and its daughters were calculated to find the three components of counting efficiency. The values of the gamma attenuation coefficients and the counting efficiencies are presented in tables and plotted the graph.
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