Activities of phenylalanine ammonia-lyase (PAL) and tyrosine ammonia-lyase (TAL) were assessed at each stage of a three-step purification of PAL. Assays were performed by high-performance liquid chromatographic (HPLC) separation and ultraviolet detection of reaction products. Use of HPLC permitted assay of low activities of PAL and TAL for periods up to approximately four and two days, respectively. HPLC also facilitated the accurate quantitation of the product of the TAL reaction, trans-p-coumaric acid, which was observed to isomerize readily under experimental conditions. PAL and TAL were associated throughout the purification procedure, with TAL activity at 0.6-1.3% of PAL activity. It was concluded that, contrary to previous reports, TAL and PAL activities are mediated by the same enzyme, or else by chromatographically very similar enzymes. 相似文献
Spherical gold nanoparticles and flat gold films are prepared in which yeast iso-1-cytochrome c (Cyt c) is covalently bound to the gold surface by a thiol group in the cystein 102 residue. Upon exposure to solutions of different pH, bound Cyt c unfolds at low pH and refolds at high pH. This conformational change causes measurable shifts in the color of the coated nanoparticle solutions detected by UV-VIS absorption spectroscopy and in the refractive index (RI) of the flat gold films detected by surface plasmon resonance (SPR) spectroscopy. Both experiments demonstrate the same trend with pH, suggesting the use of protein-covered gold nanoparticles as a simple colorimetric sensor for conformational change. 相似文献
The efficient preparation of 4-aryl-4-phenylsulfonyl cyclohexanones, containing a quaternary sulfone-bearing carbon centre, is described. Their synthesis proceeds in 38-78% overall yield by way of three steps: (i) sulfinate alkylation; (ii) methylenation; and (iii) regioselective Diels-Alder condensation with 2-trimethylsiloxybutadiene. The scope and limitations of the one-pot Mannich-type methylenation described were examined. 相似文献
Vinyl -xylylene cross-dimerizes with other xylylene-type intermediates to yield cycloadducts of the [8+6] and [6+6] type. This reaction provides a simple entry to the [4.2]paracyclophane system as well as the analogous [4.2]cyclophanes containing furan and pyrrole moieties. 相似文献
Two-dimensional patterned and controlled polyelectrolyte aggregations (e.g., tree-like ramified structures) created by microcontact printing have been demonstrated and discussed. Polyelectrolyte-micropatterned aggregations on surfaces were controlled by the micropattern size and shape of PDMS stamps. The formation of aggregates was dependent on the ink and surface conditions, and the aggregates consisted of two distinct layers; strongly adsorbed, primary uniform layers and weakly adsorbed, secondary aggregation layers positioned on top of the primary layers. The adsorption of the primary layers was strong enough not to be washed away, while the aggregated secondary layers were easily removed by washing. The aggregation of secondary layers showed typical tree-like ramified structures of fractal growth and aggregation. Directional and confined stamping led to directing and confining the growth of the fractal polyelectrolyte clusters, respectively. The micropatterned primary uniform layers were not removed by extensive washing, and they were identified by selective nickel plating and charged particle selective adsorption in which the surface formed positive and negative micropatterns. These functional and patterned surfaces have great potentials for advanced devices and sensors. 相似文献
Aminoglutethimide [3-(4-aminophenyl)-3-ethylpiperidine-2,6-dione] has been used clinically in the treatment of metastatic breast carcinoma. Inhibition of tumor growth is due to interference with estrogen biosynthesis. However, its action is not specific and its metabolism gives rise to toxic and non-inhibitory metabolites. We sought to explore the impact of relocating the amino group in aminoglutethimide to the ethyl side chain. To that end, we now report the synthesis and aromatase-inhibitory activity of 3-(2′-N,N-diethylamino)ethyl-3-phenylpiperidine-2,6-dione 5. The introduction of the amino functionality on the ethyl group is accomplished via reductive animation of aldehyde 8, prepared in three steps from benzyl cyanide. The synthetic route presented can be used for the preparation of related derivatives of aminoglutethimide. 相似文献
DFT calculations have been performed with the B3LYP and MPW1K functional on the hydrogen atom abstraction reactions of ethenoxyl with ethenol and of phenoxyl with both phenol and alpha-naphthol. Comparison with the results of G3 calculations shows that B3LYP seriously underestimates the barrier heights for the reaction of ethenoxyl with ethenol by both proton-coupled electron transfer (PCET) and hydrogen atom transfer (HAT) mechanisms. The MPW1K functional also underestimates the barrier heights, but by much less than B3LYP. Similarly, comparison with the results of experiments on the reaction of phenoxyl radical with alpha-naphthol indicates that the barrier height for the preferred PCET mechanism is calculated more accurately by MPW1K than by B3LYP. These findings indicate that the MPW1K functional is much better suited than B3LYP for calculations on hydrogen abstraction reactions by both HAT and PCET mechanisms. 相似文献
The purpose of the experiment was to determine cosmic rays long-term effects on living tissue. A batch of tomato seeds were flown in orbit aboard the Long Duration Exposure Facility (LDEF) for almost 6 y. During this time, the seeds received an abundant exposure to cosmic radiation. Upon the return of the LDEF to Earth, the seeds were distributed throughout the United States and 30 foreign countries for analysis. Our university analysis included germination and growth rates as well as scanning electron microscopy (SEM) and X-ray analysis of the control as well as space exposed tomato seeds.
In analyzing the seeds under the electron microscope, usual observations were performed on the nutritional and epidermis layer of the seed. These layers appeared to be more porous in the space exposed seeds than on Earth-based control seeds. This unusual characteristic may explain the increases in the space seeds growth pattern. (Several test results showed that the space-exposed seeds germinated sooner than Earth-based seeds. Also, the space-exposed seeds grew at a faster rate.) The porous nutritional region may allow the seeds to receive necessary nutrients and liquids more readily, thus enabling the plant to grow at a faster rate.
Roots, leaves and stems were cut into small sections and mounted. After sputter coating the specimens with argon/gold palladium plasma, they were viewed under the electron microscope. Many micrographs were taken. The X-ray analysis displayed possible identifications of calcium, potassium, chlorine, copper, aluminum, silicon, phosphate, carbon, and sometimes sulfur and iron. The highest concentrations were shown in potassium and calcium. As a result of the electron interaction and X-ray production within the open seeds, the traditional layers of the space-exposed seed gave peaks of Mg, P and S, while the Earth seed gave an iron peak, which was not detected in the space-exposed seed because of electron beam positioning difference. The space-exposed seed and the Earth-control seed specimens displayed high concentrations of copper. 相似文献