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191.
Serial increase in the thermal stability of 3-isopropylmalate dehydrogenase from Bacillus subtilis by experimental evolution.
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S. Akanuma A. Yamagishi N. Tanaka T. Oshima 《Protein science : a publication of the Protein Society》1998,7(3):698-705
We improved the thermal stability of 3-isopropylmalate dehydrogenase from Bacillus subtilis by an in vivo evolutionary technique using an extreme thermophile, Thermus thermophilus, as a host cell. The leuB gene encoding B. subtilis 3-isopropylmalate dehydrogenase was integrated into the chromosome of a leuB-deficient strain of T. thermophilus. The resulting transformant showed a leucine-autotrophy at 56 degrees C but not at 61 degrees C and above. Phenotypically thermostabilized strains that can grow at 61 degrees C without leucine were isolated from spontaneous mutants. Screening temperature was stepwise increased from 61 to 66 and then to 70 degrees C and mutants that showed a leucine-autotrophic growth at 70 degrees C were obtained. DNA sequence analyses of the leuB genes from the mutant strains revealed three stepwise amino acid replacements, threonine-308 to isoleucine, isoleucine-95 to leucine, and methionine-292 to isoleucine. The mutant enzymes with these amino acid replacements were more stable against heat treatment than the wild-type enzyme. Furthermore, the triple-mutant enzyme showed significantly higher specific activity than that of the wild-type enzyme. 相似文献
192.
S-腺苷甲硫氨酸的研究现状及应用前景 总被引:7,自引:0,他引:7
介绍了S-腺苷甲硫氨酸的制备方法及稳定性研究现状,并对其临床应用及市场前景进行了分析。 相似文献
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从不同区域土壤中分离细菌:对其进行氨苄青碡素、卡那霉素和氯霉素的抗性测试,以及抗药性质粒分析。结果表明,对照区和生活区土壤细菌抗氨苄青霉素和卡那霉素菌株比例未见显著性差异,未检出抗氯霉素细菌。保护区中抗氨苄青霉素、卡那霉素菌株含质粒比例均为18.2%,生活区中抗氨苄青霉素和卡那霉素菌株含质粒比例分别为36.4%和27.3%。随机抽提质粒转化无抗忡菌,表明部分抗菌素抗性基因是由质粒携带。实验结果认为本地土壤中抗菌素抗性菌分布差异尚未有显著性表现。 相似文献
195.
在室内模拟重金属铜的持续胁迫或者短期加热(18 h,40℃)的瞬时胁迫条件下,以大麦叶粉短期分解过程代表土壤功能,研究了土壤食细菌线虫对土壤生态功能稳定性(抗性和恢复力)的影响.结果表明,在未施加任何胁迫对照处理中和铜胁迫条件下,食细菌线虫在一定程度上有促进土壤微生物活性的趋势.在施加铜胁迫后第15天,接种食细菌线虫导致土壤基础呼吸显著增加,并且接种食细菌线虫处理的土壤功能抗性显著高于未接种线虫处理.而在热胁迫条件下,接种食细菌线虫对土壤基础呼吸和土壤微生物活性没有显著影响,且接种食细菌线虫处理的土壤功能抗性低于未接种线虫处理.在两种胁迫条件下,接种食细菌线虫反而降低了土壤功能的恢复力. 相似文献
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198.
《Chronobiology international》2013,30(6):832-841
Circadian rhythms are ≈24?h oscillations in physiology and behavior, and disruptions have been shown to have negative effects on health. Wrist skin temperature has been used by several groups as a valid method of assessing circadian rhythms in humans. We tested the hypothesis that circadian temperature amplitude (TempAmp) and stability (TempStab) would significantly differ among groups of healthy young men of varying adiposities, and that we could identify physiological and behavioral measures that were significantly associated with these temperature parameters. Wrist skin temperatures taken at 10?min intervals for 7 consecutive days were determined in 18 optimal (OGroup), 20 fair (FGroup) and 21 poor (PGroup) %Fat grouped young men and subsequently analyzed using available validated software. Body composition, cardiorespiratory fitness, actigraphy, daily nutritional and sleep data, and fasting lipid, insulin and glucose concentration measures were also determined. Significant changes in TempAmp and TempStab parameters in subjects with a single metabolic syndrome (MetS) risk factor compared to those with no MetS factors was observed. In addition, stepwise multivariate regression analyses showed that 50% of the variance in TempAmp was explained by actigraphy (mean steps taken per day; MSTPD), cardiorespiratory fitness, and late night eating per week (#LNE); and 57% in TempStab by MSTPD, time spent in moderate-to-vigorous activity per day, fat mass, and #LNE. Overwhelmingly, physical activity was the most important measure associated with the differences in circadian rhythm parameters. Further research is warranted to determine the effects of increasing the amount and timing of physical activity on the status of the circadian system in a variety of populations. 相似文献
199.
利用球孢链霉菌发酵液消化双歧杆菌细胞壁提取质粒的研究 总被引:1,自引:0,他引:1
目的寻找一种经济适用的提取双歧杆菌质粒的方法。方法利用球孢链霉菌发酵产生的变溶菌素来消化双歧杆菌细胞壁,提取质粒,并与商业化溶菌酶法比较。结果球孢链霉菌发酵液与溶菌酶均成功提取到质粒。结论利用球孢链霉菌发酵液提取质粒经济简便。 相似文献
200.