Proximal ligand electron donation and reactivity of the cytochrome P450 ferric-peroxo anion

CYP125 from Mycobacterium tuberculosis catalyzes sequential oxidation of the cholesterol side-chain terminal methyl group to the alcohol, aldehyde, and finally acid. Here, we demonstrate that CYP125 simultaneously catalyzes the formation of five other products, all of which result from deformylation of the sterol side chain. The aldehyde intermediate is shown to be the precursor of both the conventional acid metabolite and the five deformylation products. The acid arises by protonation of the ferric-peroxo anion species and formation of the ferryl-oxene species, also known as Compound I, followed by hydrogen abstraction and oxygen transfer. The deformylation products arise by addition of the same ferric-peroxo anion to the aldehyde intermediate to give a peroxyhemiacetal that leads to C-C bond cleavage. This bifurcation of the catalytic sequence has allowed us to examine the effect of electron donation by the proximal ligand on the properties of the ferric-peroxo anion. Replacement of the cysteine thiolate iron ligand by a selenocysteine results in UV-vis, EPR, and resonance Raman spectral changes indicative of an increased electron donation from the proximal selenolate ligand to the iron. Analysis of the product distribution in the reaction of the selenocysteine substituted enzyme reveals a gain in the formation of the acid (Compound I pathway) at the expense of deformylation products. These observations are consistent with an increase in the pK(a) of the ferric-peroxo anion, which favors its protonation and, therefore, Compound I formation.     

An in situ M?ssbauer study using synchrotron radiation

We have been developing a system for in situ M?ssbauer studies using synchrotron radiation (SR) to elucidate the mechanism of hydrogenation processes. In the system, samples reacts in a pressure-temperature chamber and SR-based M?ssbauer spectra using variable-frequency nuclear monochromator and energy spectra of inelastic nuclear resonant scattering (NRS) of SR are measured. As a feasibility study, the temperature dependence of the M?ssbauer and inelastic NRS spectra of ⁵⁷Fe in c-GdFe₂H₃ under vacuum were measured. In both spectra, clear differences were observed between 373?K and 573?K. These differences can be interpreted by the change of microscopic environment around Fe at the dehydrogenation. Thus, it is confirmed that this system works well enough to perform the in-situ M?ssbauer study on the dehydrogenation of c-GdFe₂H₃.     

Novel UV devices on high-quality AlGaN using grooved underlying layer

A grooved Al_0.25Ga_0.75N underlying layer on an AlN-coated sapphire substrate was used to grow crack free and low dislocation density Al_0.25Ga_0.75N to successfully realize high-performance UV A light emitters. A light-emitting diode grown on a grooved AlGaN underlying layer exhibited an output power of 12 mW at a DC current of 50 mA for a peak emission wavelength of 345 nm with an external quantum efficiency of 6.7%, which is the highest to date in this wavelength region. We also fabricated UV A laser diodes with an emission wavelength of 356 nm at a pulsed injection current of 414 mA.     

Enzyme electrodes using ultrafiltration membranes as enzyme carriers

Two kinds of commercially available ultrafiltration membranes were used for binding enzymes. These enzyme-bound membranes were connected with oxygen electrodes to build up enzyme electrodes. Quantitative assays of glucose, sucrose, and hydrogen peroxide were carried out using these enzyme electrodes in concentration ranges for glucose from 1 to 20 mg/dl, sucrose from 0.5 to 5 mg/ml, and hydrogen peroxide from 5 to 200 ppm. Similarly, D-alanine was measured in the range 0.005 to 0.05 mg/ml, but the calibration curve was not a straight line.     

Nitrogen-14 nuclear quadrupole resonance study of hydrazine monohydrate

¹⁴N NQR in hydrazine monohydrate has been investigated from 4.2 K to 140 K. A molecular motion with an activation energy of about 7.5 kcal/mol became active at about 120 K. Echo envelope modulation due to intramolecular dipolar coupling was observed.     

完全图的素圈因子分解

图的因子理论是图论研究中最活跃的课题之一.其中心问题是把一个图分解成具有给定性质的因子.     

Affinity purification methods IV. The amino(2-hydroxy)propyl ether-leash in bioselective sorbents

The amino(2-hydroxy)propyl ether derivative of agarose is obtained by treating the gel in 0.3 M NaOH with epibromohydrin at 30°C for 4 h, followed by a 16-h reaction with 1 M NH₄OH. The derivative is nonionic and chemically stable. Established coupling methods can be used to attach biochemical substances to this amino-leash. A variety of reaction parameters have been studied to optimize the epibromohydrin reaction step. It is shown that the amino-leash agarose gel can be readily used to prepare hydrophobic sorbents, affinity sorbents, immobilized enzymes, and immunosorbents.