A set of 11 expression vectors was constructed, each of themharbouring a cloning cassette under the control of the promoter.Some of these vectors enable expression of foreign proteinsin the cytoplasm, while others include a synthetic sequencecoding for a very efficient secretion signal sequence. Otherfeatures are an fl origin of replication (in plus or minus orientation)and a promoterup mutation that enhances the already very highlevel of expression from these vectors. With such a versatilevector family, cloning, sequencing and sitedirected mutagenesiscan be performed on the same vector, and the level of expressioncan be defined according to the specific constraints of a givenprotein. 相似文献
Cost-efficient Fenton-like catalysts for the removal of organic molecules in aqueous solutions were elaborated by a simple process. Porous activated carbons (ACs) were directly impregnated with a precursor solution using the wet impregnation method. Their efficiency as Fenton-like catalysts was studied. Photo-Fenton tests were performed to establish the performance of the prepared Fe-impregnated activated carbons in relation to the degradation of an organic pollutant (Indigo Carmine) model in aqueous solution, under different conditions. Photo-catalytic tests were carried out by means of a laboratory photo-reactor (UV-Consulting Peschl). The influence of several parameters such as solution pH value, initial concentration of the model pollutant, and hydrogen peroxide dose on the process performance was investigated. The ACs and prepared catalysts were characterized by nitrogen adsorption-desorption isotherms at 77 K, SEM, and thermogravimetric analyses. The total Fe content of the synthesized composites was estimated by the phenanthroline method using UV-vis spectrophotometry. The results show an increase in the degradation rate when the heterogeneous photo-Fenton process is conducted with an ozone generating UV lamp. 相似文献
Specific molecular interactions involved in catalysis by antibody 6D9 were investigated by site-directed mutagenesis. The catalytic antibody 6D9, which was generated against a transition state analog (III), hydrolyzes a non-bioactive chloramphenicol monoester derivative (I) to produce chloramphenicol (II). Construction of a three-dimensional molecular model of 6D9 and sequence comparison within a panel of related antibodies suggested candidates for catalytic residues, His (L27d), Tyr (L32), Tyr (H58) and Arg (H100b); these were targeted for the site-directed mutagenesis study. The Y-H58-F and R-H100b-A mutants possessed catalytic activities comparable to that of the wild-type, and the Y-H58-H and Y-L32-F mutant displayed an approximately fivefold decrease in k(cat)/Km. In the transition state analysis, the plots of logK(TSA) versus log(k(cat)/Km) for the mutants are linear, with a slope of approximately 1.0, indicating that the entire hapten-binding energy in the mutants is also utilized to bind the transition state and to accelerate the catalysis. In addition, a dramatic change in the catalytic activity was observed when the histidine residue (27d) in the CDR1 light chain was replaced with alanine. The H-L27d-A mutant had no detectable catalytic activity. This mutation led to a large, 40-fold reduction in transition state binding, with no change in substrate binding. Coupled with the previous kinetic studies and chemical modifications of the intact 6D9 antibody, this mutagenesis study has demonstrated that His L27d plays an essential role in stabilization of the transition state, the mechanism of catalysis by the 6D9 antibody. 相似文献
The stroma plays a fundamental role in the function of different glandular systems. In the prostate, the stroma is responsible for the development and maintenance of the differentiated state of the epithelium. Nicotine induces tobacco dependence and promotes morphological alterations in the epithelial compartment. However, its effects on the prostate stroma are unclear. The objective of this study was to evaluate the morphology of the stromal microenvironment in the ventral prostate lobe of rats submitted to chronic nicotine administration. Twenty rats (Rattus norvegicus) were divided into two groups: 10 animals received subcutaneous nicotine and 10 animals received physiological saline by the same route. After treatment, samples were collected from the ventral prostate lobe, processed and submitted to histology, histochemistry, and ultrastructural analysis by transmission and scanning electron microscopy. The level of circulating testosterone was also analyzed. The results showed a significant increase in the density of type I collagen (56.3% to 85.9%, P < 0.01) and a decrease in the density of type III collagen (43.7% to 14.1%, P < 0.01). In addition, there was a qualitative increase in elastic fibers and in the number of smooth muscle cells with a secretory phenotype. Circulating testosterone levels were significantly reduced (898.3 to 363.1 ng/mL, P < 0.01). The results showed that nicotine modifies different components of the prostate stroma, suggesting that this drug is a risk factor for morphofunctional alterations in the prostate gland. 相似文献
Activated-carbon pore size tailoring is usually achieved by pore size reduction, pore size widening or more rarely by direct activation. Successive widening cycles composed of an initial molecular oxygen sorption step, followed by a carbonization step under nitrogen, have been applied to three different materials in order to study their gradual pore size modifications. For years, the whole microporosity obtained after several cycles is known to present better pore size distribution than those inherited from conventional activations. Moreover, as shown in the present paper, the gradual obtained microporosities cover a wide and valuable range of porous textures highly dependent on the initial material origin and initial activation. Gradual mean pore size evolutions of 1 or 2 Å per cycle were observed linked to a simultaneous increase in microporous specific volume in the case of pitch-based and coconut activated carbons, respectively. Comparatively, the microporous specific volume of a commercial coconut carbon molecular sieve was increased by 26% without modification of its mean pore size and therefore of its sieving effect. Those results have been used to test a simple textural model of activated carbon porosity proposed in the recent literature. 相似文献
Two complementary wearing off cycling methods based on an initial wet oxidation in a sodium hypochlorite solution or an initial dry oxidation under air, both followed by a thermal pyrolysis under nitrogen, have been applied to a same carbon molecular sieve to study its gradual pore structure modifications. The changes in microporous properties resulting from these cycles were studied by N2 physisorption at 77 K and analyzed by using the Dubinin–Radushkevich equation. The observed textural behaviour is different from those usually observed using conventional activation processes. The surface complexes created on the surface of carbon by each NaOCl oxidation were characterized by temperature-programmed desorption (TG-TPD-MS), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). Corresponding surface functional species have been identified and quantified.
Each of the two methods leads to the formation of two distinct microporous domains developed on the obtained modified CMS series. The gradual mean pore size values of one of those domains are common to the two series while the others are much more enlarged by the oxygen than by the NaOCl treatments. Therefore, the two methods lead to complementary data allowing experimental differentiation of the different porosities encountered in activated carbons. Such series of materials of common origin and surface chemistry but different gradual textural properties are of great interest for activated carbons structural studies as well as for characterization technique improvements. 相似文献