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131.
132.
利用脂肪酶在有机溶剂中催化对映选择性酯化反应对外消旋薄荷醇进行了有效的光学拆分。对分别使用酸酐和相应的游离羧酸作酰基给体时的反应性能进行了比较。发现酸酐的反应性远高于对应的游离羧酸,但在酶的催化作用下酸酐易水解成为游离羧酸;在微水系统中使用过高浓度的酸酐会导致酶缺水而失活,同时会促进手性醇的非选择性酯化,从而降低产物的光学纯度。然而,在连续流加丙酸酐的半批式反应系统中,所有这些缺点均可有效地克服。与使用游离丙酸的批式反应系统相比,dl-薄荷醇的反应时间缩短了一半,酶的稳定性大幅度提高,而产物l薄荷醇酯的光学纯度不相上下(>98%e)。  相似文献   
133.
应用同工酶分析方法,测定北京市东灵山区两个分别代表干旱和湿润生境的辽东栋(QuercusliaotungensisKoiz.)群体的遗传结构。共分析统计了13 个酶系统30 个位点。结果表明:辽东栎群体内部存在丰富的遗传变异(多态位点百分率为86.6% ,等位基因平均数为2.25)。两群体遗传结构的相似性程度很高(D= 0.029, GST= 0.048);但在个别位点上仍存在较大差异,这些差异的产生可能与对小生境的适应有关。对不同年龄段的初步分析结果显示,基因频率的动态变化可能有其适应意义  相似文献   
134.
Alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH), the principal enzymes responsible for oxidative metabolism of ethanol, exist in multiple, genetically determined molecular forms. Widely different kinetic properties in some of these isozymes account for the individual differences in alcohol sensitivity. In this study we used the polymerase chain reaction/restriction fragment length polymorphism method to determine the genotypes of the ADH2 and ALDH2 loci of alcoholic and nonalcoholic Chinese living in Shanghai. We also investigated the subjects' drinking patterns by means of semistructured interviews. The alcoholics had significantly lower frequencies of the ADH22 and ALDH22 alleles than did the nonalcoholics, suggesting the inhibitory effects of these alleles for the development of alcoholism. In the nonalcoholic subjects, ADH22 had little, if any, effect, despite the significant effect of the ALDH22 allele in decreasing the alcohol consumption of the individual. Taken together, these results fit the proposed hypothesis for the development of alcoholism, i.e., drinking behavior is greatly influenced by the individual's gentoypes of alcohol-metabolizing enzymes, and the risk of becoming alcoholic is proportionate with the ethanol consumption of the individual.  相似文献   
135.
A three-dimensional structure of the NAD site of Escerichia coli transhydrogenase has been predicted. The model is based on analysis of conserved residues among the transhydrogenases from five different sources, homologies with enzymes using NAD as cofactors or substrates, hydrophilicity profiles, and secondary structure predictions. The present model supports the hypothesis that there is one binding site, located relatively close to the N-terminus of the α-subunit. The proposed structure spans residues α145 to α287, and it includes five β-strands and five α-helices oriented in a typical open twisted α/β conformation. The amino acid sequence following the GXGXXG dinucleotide binding consensus sequence (residues α172 to α177) correlates exactly to a typical fingerprint region for ADP binding βαβ folds in dinucleotide binding enzymes. In the model, aspartic acid α195 forms hydrogen bonds to one or both hydroxyl groups on the adenosine ribose sugar moiety. Threonine α196 and alanine α256, located at the end of βB and βD, respectively, create a hydrophobic sandwich with the adenine part of NAD buried inside. The nicotinamide part is located in a hydrophobic cleft between αA and βE. Mutagenesis work has been carried out in order to test the predicted model and to determine whether residues within this domain are important for proton pumping directly. All data support the predicted structure, and no residue crucial for proton pumping Was detected. Since no three-dimensional structure of transhydrogenase has been solved, a well based tertiary structure prediction is of great value for further experimental design in trying to elucidate the mechanism of the energy-linked proton pump. © 1995 Wiley-Liss, Inc.  相似文献   
136.
Type IV pre-pilin leader peptidase was demonstrated to be required for protein secretion, in addition to its involvement in biogenesis of type IV pili. The type IV pre-pilin leader peptidase gene of Xanthomonas campestris pv. campestris was located on a 3 kb Acc l fragment on account of its hybridization with the DNA fragment containing the type IV pre-pilin leader-peptidase gene pilD/xcpA of Pseudomonas aeruginosa . Sequencing of the cloned fragment revealed an open reading frame (ORF) (designated xpsO ) of 287 amino acid residues. A protein with an apparent molecular mass of approximately 32.5 kDa was synthesized in vitro from a DNA fragment containing the xpsO gene. The amino acid sequence shares 50% identity with that of PilD throughout the entire sequence. Among other type IV pre-pilin leader peptidases, XpsO is unique in not having the two conserved -CXXC- motifs in a cytoplasmic domain. Instead, new motifs were noted when the protein was compared with XpsE, which is another member of the extracellular protein-secretion machinery. When the xpsO gene was introduced into the pilD mutant of P. aeruginosa , both the sensitivity against infection with the pilus-specific phage PO4 and the ability to secrete extracellular protein were recovered. Furthermore, immunoblot analysis indicated that the P. aeruginosa pilin was apparently processed in vivo by the xpsO gene product.  相似文献   
137.
138.
将酶电极应用于发酵糖的测定时。与糖共存的乙醇常常会影响测糖的准确性,通过对葡萄糖氧化酶(GOD)电极的研究,探讨了乙醇对测糖酶电极测定影响,进而研制出抗干扰的GOD酶电极,若是GOD电极的酶膜通过夹心法制备.在乙醇含量为0.1%(V/V)时·即产生显著的影响,使测定结果偏大4.3%,且乙醇的影响随浓度的升高而增大,若用尼龙网固定GOD膜,GOD电极在测定20mmol/L和5mm01/L左右的葡萄糖溶液时,含量高达9%的乙醇仍未对测定产生显著的影响.表现出良好的不受乙醇干扰的特性,并且,该尼龙网GOD电极具有良好的重复性、稳定的响应活性及较长的保存期.  相似文献   
139.
140.
低高径比喷射环流生化反应器流体力学和发酵性能的研究   总被引:5,自引:0,他引:5  
对高径比s≤2.5喷射环流生化反应器的流体力学和传质特性进行了系统的研究,选出反应器的最佳结构,关联出氧的体积传递系数(kLa)表达式。在此基础上,进行了谷氨酸发酵试验,摸索出用该设备进行各氨酸发酵的最佳工艺条件,使5批一次性投糖发酵的糖酸转化率达到50%以上。  相似文献   
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