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101.
Recent experimental advances have shown that enzymes are flexible molecules, and point to a direct link between dynamics and
catalysis. Movements span a wide time range, from nano- to milli-seconds. In this paper we introduce two aspects of enzyme
flexibility that are treated with two appropriate techniques. First, transition path sampling is used to obtain an unbiased
picture of the transition state ensemble in chorismate mutase, as well as its local flexibility and the energy flow during
the chemical step. Second, we consider the binding and release of substrates in L-rhamnulose-1-phosphate aldolase. We have calculated the normal modes of the enzyme with the elastic network model. The lowest
frequency modes generate active site deformations that change the coordination number of the catalytic zinc ion. The coordination
lability of zinc allows the binding and release of substrates. Substitution of zinc by magnesium blocks the exchange of ligands.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
102.
Opposite enantiomers of a chiral fragrance may exhibit different olfactory activities making a synthesis in high enantiomeric purity commercially and scientifically interesting. Accordingly, the asymmetric synthesis of four chiral odorants, Fixolide, Phenoxanol, Citralis, and Citralis Nitrile, has been investigated with the aim to develop practically feasible processes. In the devised synthetic schemes, the key step that leads to the formation of the stereogenic center is the homogeneous asymmetric hydrogenation of a prochiral olefin. By an appropriate choice of the catalyst and the reaction conditions, Phenoxanol, Citralis, and Citralis Nitrile were obtained in high enantiomeric purity, and odor profiles of the single enantiomers were determined. 相似文献
103.
von Langermann J Guterl JK Pohl M Wajant H Kragl U 《Bioprocess and biosystems engineering》2008,31(3):155-161
The application of unusual high pH-values within enzymatic cyanohydrin synthesis has been investigated. Usually enzymatic
cyanohydrin synthesis in two-phase systems requires low pH-values within the aqueous phase to suppress the non-enzymatic side
reaction. In contrast, we investigated the usage of pH-values above pH 6 by using the highly enantioselective (S)-selective hydroxynitrile lyase from Manihot esculenta. With these unusual reaction conditions also the unfavorable substrate 3-phenoxy-benzaldehyde can be converted by the wild
type enzyme with excellent conversion and enantiomeric excess yielding pure (S)-3-phenoxy-benzaldehyde cyanohydrin with an enantiomeric excess of 97%. Although the variant MeHNL–W128A shows a higher activity with respect to this reaction, the enantioselectivity was reduced (85% e.e.(S)). Additionally, a new continuous spectroscopic cyanohydrin assay monitoring the formation of 3-phenoxy-benzaldehyde cyanohydrin
was developed.
Dedicated to Prof. Dr. Christian Wandrey on the occasion of his 65th birthday. 相似文献
104.
105.
The Baeyer-Villiger monooxygenase (BVMO) BmoF1 from Pseudomonas fluorescens DSM 50106 was shown before to enantioselectively oxidize different 4-hydroxy-2-ketones to the corresponding hydroxyalkyl acetates, being the first example of a BVMO-catalyzed kinetic resolution of aliphatic acyclic ketones. However, the wild-type enzyme exhibited only moderate E values (E approximately 55). Thus, the enantioselectivity was enhanced by means of directed evolution and optimization of reaction conditions since it was found that higher E values (E approximately 70 for wild-type BmoF1) could already be obtained when performing biotransformations in shake flasks rather than small tubes. In a first step, random mutations were introduced by error-prone polymerase chain reaction, and BmoF1 mutants (>3,500 clones) were screened for improved activity and enantioselectivity using a microtiter-plate-based screening method. Mutations S136L and L252Q were found to increase conversion compared to wild type, while several mutations (H51L, F225Y, S305C, and E308V) were identified enhancing the enantioselectivity to a varying extent (E approximately 75-90). In a second step, beneficial mutations were recombined by consecutive cycles of QuikChange site-directed mutagenesis resulting in a double mutant (H51L/S136L) showing both improved conversion and enantioselectivity (E approximately 86). 相似文献
106.
Karabach YY Kirillov AM Haukka M Kopylovich MN Pombeiro AJ 《Journal of inorganic biochemistry》2008,102(5-6):1190-1194
The new inorganic 1D coordination polymer [Cu2(H3tea)2(μ4-pma)]n has been prepared, via self-assembly in aqueous medium, from copper(II) nitrate, triethanolamine (H3tea), pyromellitic acid (H4pma) and lithium hydroxide, and characterized by IR spectroscopy, elemental and single-crystal X-ray diffraction analyses. This compound and the related 2D polymer [Cu2(μ-H2tea)2{μ3-Na2(H2O)4}(μ6-pma)]n · 10nH2O are shown to mimic the alkane partial oxidation activity of the multicopper particulate methane monooxygenase, acting as catalysts precursors for the peroxidative oxidation of cyclohexane into cyclohexanol and cyclohexanone, by hydrogen peroxide (as green oxidant) and at room temperature in acidic MeCN/H2O medium. An overall yield (based on cyclohexane) of 29% has been achieved. 相似文献
107.
Simone L. Pival 《FEBS letters》2008,582(29):4095-4099
Substitution of active-site Tyr-51 by Ala (Y51A) disrupted the activity of Candida tenuis xylose reductase by six orders of magnitude. External bromide brought about unidirectional rate enhancement (≈2 × 103-fold at 300 mM) for NAD+-dependent xylitol oxidation by Y51A. Activity of the wild-type reductase was dependent on a single ionizable protein group exhibiting a pK of 9.2 ± 0.1 and 7.3 ± 0.3 in the holo-enzyme bound with NADH and NAD+, respectively. This group which had to be protonated for xylose reduction and unprotonated for xylitol oxidation was eliminated in Y51A, consistent with a catalytic acid-base function of Tyr-51. Bromide may complement the xylitol dehydrogenase activity of Y51A by partly restoring the original hydrogen bond between the reactive alcohol and the phenolate of Tyr-51. 相似文献
108.
Particle-tethered NADH for production of methanol from CO(2) catalyzed by coimmobilized enzymes 总被引:1,自引:0,他引:1
Efficient cofactor regeneration and reuse are highly desired for many important biotransformation applications. Here we show for the first time that cofactor NAD(H) covalently attached to micro particles, which can be easily recovered and reused, effectively mediated multistep reactions catalyzed by enzymes that were also immobilized with the micro particles. Such an immobilized enzyme-cofactor catalytic system was examined for the production of methanol from CO(2) with in situ cofactor regeneration. Four enzymes including formate, formaldehyde, alcohol, and glutamate dehydrogenases were coimmobilized using the same particles as that used for cofactor immobilization (enzymes and cofactor were immobilized separately). Reactions were performed by bubbling CO(2) in a suspension solution of the particle-attached enzymes and cofactor. It appeared that the collision among the particles afforded sufficient interactions between the cofactor and enzymes, and thus enabled the sequential transformation of CO(2) to methanol along with cofactor regeneration. For a 30-min batch reaction, a productivity of 0.02 micromol methanol/h/g-enzyme was achieved. That was lower than but comparable to the 0.04 micromol methanol/h/g-enzyme observed for free enzymes and cofactor at the same reaction conditions. The immobilized system showed fairly good stabilities in reusing. Over 80% of their original productivity was retained after 11 reusing cycles, with a cumulative methanol yield based on the amount of cofactor reached 127%. That was a promising enhancement in cofactor utilization as compared to the single-batch yield of 12% observed with free enzymes and free cofactor. 相似文献
109.
110.
T. A. Chupakhina V. O. Kur'yanov V. Ya. Chirva R. Ya. Grigorash S. A. Kotlyar G. L. Kamalov 《Russian Journal of Bioorganic Chemistry》2004,30(3):301-303
The crown ether-catalyzed glycosylation of phenol, 4-methoxyphenol, and 4-nitrophenol was studied under phase transfer conditions in solid–liquid system. The asymmetric dibenzocrown esters are superior to [3.3]dibenzo-18-crown-6 and 15-crown-5 in the catalysis of these reactions. 相似文献