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111.
Irina G. Gazaryan Maya Yu. Rubtsova Yuri L. Kapeliuch José Neptuno Rodriguez-Lopez L. Mark Lagrimini Roger N. F. Thorneley 《Photochemistry and photobiology》1998,67(1):106-110
The properties of a newly isolated anionic tobacco peroxidase from transgenic tobacco plants overexpressing the enzyme have been studied with respect to the chemiluminescent reaction of luminol oxidation. These were compared to the properties of horseradish peroxidase in the cooxidation of luminol and p -iodophenol, the enhanced chemiluminescence reaction. The pH, luminol and hydrogen peroxide concentrations were optimized for maximum sensitivity using the tobacco enzyme. The detection limit for the latter under the optimal conditions (2.5 m M luminol, 2 m M hydrogen peroxide, 100 m M Naborate buffer, pH 9.3) was about 0.1 p M , which is at least five times lower than that for horseradish peroxidase in enhanced chemiluminescence with p -iodophenol. The rate constants for the elementary steps of the enzyme-catalyzed reaction have been determined: k 1 = 4.9 × 106 M −1 s1 , k 2 = 7.3 × 106 M −1 s−1 , k 3 = 2.1 × 106 M −1 s−1 (pH 9.3). The similarity of these rate constants is unusual for plant peroxidases. The high catalytic activity of tobacco peroxidase in the luminescent reaction is explained by the high reactivity of its Compound II toward luminol and the high stability of the holoenzyme with respect to heme dissociation. This seems to be a unique property of this particular enzyme among other plant peroxidases. 相似文献
112.
Mass spectrometric analysis of ceramide perturbations in brain and fibroblasts of mice and human patients with peroxisomal disorders 总被引:2,自引:0,他引:2
Pettus BJ Baes M Busman M Hannun YA Van Veldhoven PP 《Rapid communications in mass spectrometry : RCM》2004,18(14):1569-1574
In this study, the levels and composition of ceramides in brains of newborn mice lacking peroxisomes (Pex5-/-, Zellweger mice) were analyzed using normal-phase high-performance liquid chromatography/atmospheric pressure chemical ionization mass spectrometry (HPLC/APCI-MS). Total ceramide compositions were found to be comparable to that of control animals. However, a minor ceramide species, containing hexacosanoic/hexacosenoic acid as the amide fatty acid, was 9-fold increased. Also, in the sphingomyelin-derived ceramides this species was elevated. Subsequent analysis of extracts from fibroblasts of Pex5-/- mice and mice with a defective peroxisomal beta-oxidation (lacking D-specific multifunctional protein 2 (MFP2)), revealed, again, a similar rise in this particular ceramide. Further, this ceramide was elevated in human X-ALD fibroblasts as well. Whether C26:1/0-ceramide is linked to some of the pathology seen in Zellweger syndrome remains to be investigated. However, an increase in this sphingolipid can be considered as a diagnostic criterion for diseases caused by defects in peroxisome biogenesis or peroxisomal beta-oxidation. 相似文献
113.
Triolo A Russina O Hardacre C Nieuwenhuyzen M Gonzalez MA Grimm H 《The journal of physical chemistry. B》2005,109(46):22061-22066
A detailed investigation on the nature of the relaxation processes occurring in a typical room temperature ionic liquid (RTIL), namely, 1-butyl-3-methyl imidazolium hexafluorophosphate ([bmim][PF(6)]), is reported. The study was conducted using both elastic and inelastic neutron scattering over a wide temperature range from 10 to 400 K, accessing the dynamic features of both the liquid and glassy amorphous states. In this study, the inelastic fixed energy scan technique has been applied for the first time to this class of materials. Using this technique, the existence of two relaxation processes below the glass transition and a further diffusive process occurring above the glass-liquid transition are observed. The low temperature processes are associated with methyl group rotation and butyl chain relaxation in the glassy state and have been modeled in terms of two Debye-like, Arrhenius activated processes. The high temperature process has been modeled in terms of a Kohlraush-Williams-Watts relaxation, with a distinct Vogel-Fulcher-Tamman temperature dependence. These results provide novel information that will be useful in rationalizing the observed structural and dynamical behavior of RTILs in the amorphous state. 相似文献
114.
Several radical cyclisation reactions involving indoles are described. Most notably, we have shown that radical additions to C3 of an indole are frequently facile. A dichotomy in the course of radical cyclisation reactions to C2 of the indole has also been exposed wherein 6-endo-trig cyclisations are propagated by the loss of a hydrogen atom from C2 while 5-exo-trig cyclisations are propagated by hydrogen atom abstraction at C3 from tributyltin hydride. Cyclisations involving the addition of indolyl radical intermediates to arenes have also been demonstrated. 相似文献
115.
Talhout R Villa A Mark AE Engberts JB 《Journal of the American Chemical Society》2003,125(35):10570-10579
The binding of a series of p-alkylbenzamidinium chloride inhibitors to the serine proteinase trypsin over a range of temperatures has been studied using isothermal titration (micro)calorimetry and molecular dynamics simulation techniques. The inhibitors have small structural variations at the para position of the benzamidinium ion. They show small differences in relative binding affinity but large compensating differences in enthalpy and entropy. Binding affinity decreases with increased branching at the first carbon but increases with increasing the length of a linear alkyl substituent, suggesting that steric hindrance and hydrophobic interactions play dominant roles in binding. Structural analysis showed that the backbone of the enzyme was unaffected by the change of the para substituent. In addition, binding does not correlate strongly with octanol/water partition data. To further characterize this system, the change in the heat capacity on binding, the change in solvent-accessible surface area on binding, the effect of inhibitor binding on the hydration of the active site, the pK(a) of His57, and interactions within the catalytic triad have been investigated. Although the changes in inhibitor structure are small, it is demonstrated that simple concepts such as steric hindrance, hydrophobicity, and buried surface area are insufficient to explain the binding data. Other factors, such as access to the binding site and the cost of dehydration of the active site, are of equal or greater importance. 相似文献
116.
Haijun HaoHerbert W. Roesky Yuqiang DingChunming Cui Mark SchormannHans-Georg Schmidt Mathias NoltemeyerBoris ?emva 《Journal of fluorine chemistry》2002,115(2):143-147
β-Diketiminato magnesium fluoride [{CH(CMeNAr)2}Mg(μ-F)(THF)]2·toluene (Ar=2,6-i-Pr2C6H3, 2·toluene) was synthesized. The molecular structure of 2 revealed for the first time, the double fluoro bridge feature between the two magnesium atoms with a typical MgF bond length (average 1.95 Å). 相似文献
117.
The reactions of syn-1-haloethyl p-chlorophenyl sulfoxides (halogen = Cl, Br) with main-group organometallic reagents (n-BuMgCl, MeLi, n-BuLi, s-BuLi, and t-BuLi) in THF and PhMe solvents were examined. Product distributions were analyzed to determine the extent of competing sulfoxide ligand exchange, halogen-metal exchange, and deprotonation reaction pathways. A combination of t-BuLi in PhMe was optimal for initiation of sulfoxide ligand exchange from syn-1-chloroethyl p-chlorophenyl sulfoxide. 相似文献
118.
Simple 2H-chromenes and 2H-thiochromenes form the [2+2]-adducts, tetrahydro[1]benzo(thio)pyrano[3,4-c] [1,2]diazeto[1,2-a][1,2,4]triazoles, with triazolinediones, whereas their 3- and 4-bromo and the corresponding cycloalkylamino derivatives undergo an overall etectrophilic substitution sequence. 相似文献
119.
A Pd(+2) catalyzed cyclization of a 1,6-enyne complements a thermal Alder ene reaction; a rationale invoking a remote binding site is proposed. 相似文献
120.
Small gold nanoparticles can mimic dehydrogenase activity to catalyze estradiol (E2) oxidation to estrone (E1), extending the range of nanozyme catalysis to environmentally and biologically important substrates. 相似文献