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[chemical reaction: see text]. To study the catalysis of isopentenyl diphosphate (IPP) isomerase type II from Staphylococcus aureus, which is a flavoprotein catalyzing the interconversion of IPP and dimethylallyl diphosphate, we have chemically synthesized (S)- and (R)-[2-2H]IPP and carried out stereochemical analysis of the reaction. Our results show that the C-2 deprotonation of IPP by this enzyme is pro-R stereospecific, suggesting a similar stereochemical course as the type I enzyme. 相似文献
37.
The intracellular detection of hydroxyl radical (HO*) through spin trapping/electron paramagnetic resonance (EPR) spectroscopy has been one of the great challenges in studying free radicals in biology. While 5-carboxy-5-methyl-1-pyrroline N-oxide, can specifically spin trap HO* in homogeneous solutions, the ionic nature of nitrone at physiologic pH prevents its entry into cells. We hypothesized that conversion of carboxyl-bearing spin probes such as nitrone into an esterase-hydrolyzable labile ester would permit intracellular localization and accumulation of the spin probes. To test the feasibility of such an approach, we prepared the model compound, 3-acetoxymethoxycarbonyl-2,2,5,5-tetramethyl-1-pyrrolidinyloxyl. This ester enabled ready accumulation of spin label to mM levels in lymphocytes. We suggest that its retention within these cells was the result of intracellular hydrolysis to 3-carboxy-2,2,5,5-tetramethyl-1-pyrrolidinyloxyl. Moreover, our studies show that aminoxyl was stable in the intracellular environment. These model studies suggest a viable strategy for detecting intracellular HO* by using the acetoxymethyl ester of 5-carboxy-5-methyl-1-pyrroline N-oxide. 相似文献
38.
The uranyl chelate of ferron was investigated polarographically over the pH range 1.98–10.00 and ligand concentration 0.005–0.060.M. A reversible and diffusion controlled reduction wave was obtained, however, when ferron concentration below 0.02M and pH below 5.0, it became irreversible. The chelate species identified were UO2(HA) 2 at pH range 2.5–7.1 and UO2(OH) (A) 2?3 over pH 7.1. The electron-transfer coefficient, rate constant, diffusion coefficient and activation energy of the reduction process were determined. 相似文献
39.
R. Hristu S. G. Stanciu F.-J. Kao G. A. Stanciu 《Applied physics. B, Lasers and optics》2012,107(1):97-101
We report on the two-photon excited photoluminescence of photonic quantum ring laser structures using Ti:Sapphire femtosecond
pulsed laser. Using two-photon excited photoluminescence microscopy, we were able to image the laser structures when optically
excited and compare the results with previously obtained images on electrically pumped photonic quantum ring lasers. We also
propose a method to evaluate the Rayleigh band on the circumference of these structures. 相似文献
40.
Journal of Statistical Physics - Multiplex networks are a type of multilayer network in which entities are connected to each other via multiple types of connections. We propose a method, based on... 相似文献