丝氨酸对宁南霉素生物合成的影响

研究宁南霉素发酵过程中如何通过加入前体来提高宁南霉素的产量，进行了添加前体种类选择、前体加入量和加入时间对比实验。结果表明，丝氨酸是较佳的合成前体。添加间接前体物A和B，对宁南霉素生物合成也有明显促进作用。在发酵24、36和42h分别添加丝氨酸、前体物A和B，宁南霉素发酵效价为对照的143％、130%和11141％。     

前体对纳他霉素生物合成的影响

研究如何通过加入前体来提高生物合成纳他霉素的产量，进行了前体种类选择、前体加入量及加入时间的优化实验，结果表明，丙酸钠是比乙酸钠、丁酸钠、正丙醇更佳的纳他霉素合成前体，乙醇及正丁醇对纳他霉素生物合成无明显促进作用；在发酵24h时向发酵培养基中添加0．6％的丙酸钠．纳他霉素产量达3014．43mg／L，与不添加前体相比提高了185.8％，具有较好的工业应用价值。     

前体对洛伐他汀生物合成的影响

目的通过研究前体对洛伐他汀生物合成的影响，寻找提高洛伐他汀发酵水平的有效方法。方法本文主要考察不同前体对洛伐他汀生物合成的作用及有效前体的最佳添加浓度和添加时间。结果柠檬酸三钠是比柠檬酸铁更有效促进洛伐他汀合成的前体，最佳浓度为0．75％，在0h添加最有效；在上述条件下，洛伐他汀的产量达9134．0mg／L，与不添加前体相比提高26.8％。结论柠檬酸三钠是促进洛伐他汀合成的较适宜前体，可以提高洛伐他汀的发酵水平。     

前体对多拉菌素生物合成的影响

目的 通过研究前体对多拉菌素生物合成的影响,寻找提高多拉菌素发酵产量的有效方法.方法 本文主要考察了不同前体对多拉菌素生物合成的作用,以及有效前体的最佳添加浓度和添加时间.结果 丙酸钠是多拉菌素合成的最佳前体,在发酵96h时添加0.1％的丙酸钠,多拉菌素产量达139.89μg/mL,比对照组提高了38.2％.结论 前体的供给能显著影响多拉菌素的生物合成,补加丙酸钠能有效提高多拉菌素的发酵产量.     

芳香族氨基酸添加提高井冈霉素产量的研究

目的 通过添加芳香族氨基酸促进井冈霉素生物合成起始单位的供应,提高其发酵产量.方法 优化苯丙氨酸添加时间和浓度确定最优添加条件,分析前体代谢相关的酶活考察其影响机制.结果 确定苯丙氨酸最佳添加条件为在发酵第24h添加0.1g/L.发现37℃时苯丙氨酸的添加提高了井冈霉素A产量,但在42℃条件下提高幅度大大降低.通过分析6-磷酸葡萄糖脱氢酶酶活,发现芳香族氨基酸添加并未影响其酶活.结论 苯丙氨酸的添加能有效提高井冈霉素发酵产量近60％.苯丙氨酸的添加可能通过反馈抑制降低了戊糖磷酸途径中中间体的消耗,从而为井冈霉素合成提供了更加充足的7-磷酸景天庚酮糖.     

2007—32促进剂对发酵生产辅酶Q10的影响

目前制约发酵法工业化生产辅酶Q10的主要因素是发酵产率较低，生产成本较高。根据辅酶Q10生物合成机制和代谢途径，在发酵过程中选择性地添加有可能促进辅酶Q10合成的物质，研究其对辅酶Q10合成的影响，以期提高辅酶Q10的产量。结果表明，在培养基中适量添加VB、乙酸钠、花生油均可明显提高辅酶Q10的产量，使用正交试验优化后的促进剂组合可使辅酶Q10产量达到50．7ml／L，比对照组提高33％。[第一段]     

阿卡波糖产生菌代谢调控的研究

目的探索4种可能的调节物对阿卡波糖生物合成的调节作用,以提高阿卡波糖的发酵产量。方法根据阿卡波糖的生物合成途径,在阿卡波糖发酵的不同阶段添加不同浓度的代谢调节物质,依据阿卡波糖的发酵水平确定添加代谢调节物质的最佳时间和最佳质量浓度。结果 0 h于发酵培养基中添加1 mg.L-1碘乙酸,发酵结束时阿卡波糖的发酵单位提高了8.9%;48 h添加1 mg.L-1NaF,发酵单位提高了13.3%;72 h添加0.5 g.L-1柠檬酸钠,发酵单位提高了6.2%;48 h添加2 g.L-1莽草酸,发酵单位提高了17.3%。结论这4种化合物对阿卡波糖的生物合成都有一定的调节作用,在最佳的时间以最适的浓度添加可以提高阿卡波糖的发酵产量。     

胞壁合成对庆大霉素生物合成的影响

研究了庆大霉素低产菌株胞壁合成的控制对庆大霉素生物合成的影响。研究发现，发酵过程中外源添加青霉素能有效提高庆大霉素产量。发酵６０ｈ时，添加２０ｕ／ｍｌ的青霉素１次能使摇瓶发酵效价提高１．１７倍；罐发酵效价提高０．６２倍。采用多次青霉素添加工艺能发酵效价提高０．７８倍。     

紫杉醇生物合成的研究进展

紫杉醇是一种抗癌新药。紫杉醇及其衍生物还具有防治移植动脉硬化、抗瘢痕形成和抗血管生成等功能。目前，人们获得紫杉醇的方法主要有以下几种：直接从红豆杉中提取；化学全合成；化学半合成；细胞培养；内生真菌提取培养及代谢工程生产紫杉醇。已从红豆杉中克隆出了至少14个和紫杉醇生物合成相关的基因并进行了功能鉴定。紫杉醇生物合成途径的阐明带动了紫杉醇前体组合表达系统的研究。     

青霉素发酵液中苯乙酸残留量快速检测法

青霉素生物合成过程中,加入苯乙酸作前体,可以提高发酵产量;但过量的苯乙酸对青霉菌具有毒性。因此在青霉素的发酵控制中,必须定时测定其残留量,并据此添加适量苯乙酸,以获得最佳生产效果。青霉素发酵液中苯乙酸残留量的测定,     

Seasonal variation of artemisinin and its biosynthetic precursors in plants of Artemisia annua of different geographical origin: proof for the existence of chemotypes

The time course of the levels of artemisinin, its biosynthetic precursors and the biosynthetically related sesquiterpenes was monitored during a vegetation period of Artemisia annua plants of different geographical origin. Considerable differences in contents of artemisinin and its direct precursors artemisinic acid and dihydroartemisinic acid were found between these A. annua's. For the first time the A. annua plants of different geographical origin were found to belong to different chemotypes. A chemotype with a high artemisinin level was found to have also a high dihydroartemisinic acid level but a relatively low artemisinic acid level. Reversibly, a chemotype with low levels of artemisinin and dihydroartemisinic acid contained a high artemisinic acid level. Artemisinic acid is considered to be the direct precursor of dihydroartemisinic acid in the biosynthetic pathway of artemisinin. The observed accumulation of artemisinic acid in one of the A. annua chemotypes may indicate the presence of a rate-limiting step in the biosynthetic pathway of artemisinin. The enzymatic reduction of artemisinic acid into dihydroartemisinic acid is probably a "bottle neck" in the biosynthetic pathway of artemisinin in varieties with high artemisinic acid and consequentially low artemisinin levels. After a night-frost period, the level of artemisinin was increased, in the Vietnamese A. annua plants, while the dihydroartemisinic acid level was decreased. This phenomenon is in accordance with our hypothesis that stress triggers the conversion of dihydroartemisinic acid to artemisinin. It is suggested that the presence of high levels of dihydroartemisinic acid may be an adaptation to stress conditions (e.g., night-frost), during which relatively high levels of 1O2 are formed. Dihydroartemisinic acid gives the plant protection by reacting with these reactive oxygen species yielding artemisinin as stable end-product.     

重组大肠杆菌产番茄红素的研究进展

番茄红素是一种重要的类胡萝卜素,作为一种强抗氧化剂,具有重要的药用价值。随着番茄红素合成途径的阐明及分子生物学技术的发展,运用基因工程手段生产番茄红素越来越受到研究者的青睐。本文综述了利用重组大肠杆菌生产番茄红素的研究情况和最新进展。     

Biosynthesis of astromicin and related antibiotics. I. Biosynthetic studies by bioconversion experiments

Biosynthesis of astromicin, a unique pseudodisaccharide aminoglycoside antibiotic containing 1,4-diaminocyclitol component, was investigated by isolating a variety of possible precursor compounds from mutants of Micromonospora olivasterospora in which biosynthetic pathways for astromicin were blocked. Washed mycelia of M. olivasterospora mutants converted these compounds to astromicin, which was detected by thin-layer chromatography. Since astromicin possesses one glycyl and three methyl groups, [14C]glycine and [14C]methionine should be incorporated into precursors to form astromicin. To confirm the biosynthetic pathway, formation of labeled astromicin from the precursors was examined using [1-14C]-glycine or [methyl-14C]methionine. From above results, we propose the biosynthetic pathway for astromicin as shown in Fig. 2.     

Antidepressant Effects of Abscisic Acid Mediated by the Downregulation of Corticotrophin-Releasing Hormone Gene Expression in Rats

Background:

Corticotrophin-releasing hormone (CRH) is considered to be the central driving force of the hypothalamic-pituitary-adrenal axis, which plays a key role in the stress response and depression. Clinical reports have suggested that excess retinoic acid (RA) is associated with depression. Abscisic acid (ABA) and RA are direct derivatives of carotenoids and share a similar molecular structure. Here, we proposed that ABA also plays a role in the regulation of CRH activity sharing with the RA signaling pathway.

Methods:

[₃H]-ABA radioimmunoassay demonstrated that the hypothalamus of rats shows the highest concentration of ABA compared with the cortex and the hippocampus under basal conditions.

Results:

Under acute stress, ABA concentrations increased in the serum, but decreased in the hypothalamus and were accompanied by increased corticosterone in the serum and c-fos expression in the hypothalamus. Moreover, chronic ABA administration increased sucrose intake and decreased the mRNA expression of CRH and retinoic acid receptor alpha (RARα) in the hypothalamus of rats. Furthermore, ABA improved the symptom of chronic unpredictable mild stress in model rats, as indicated by increased sucrose intake, increased swimming in the forced swim test, and reduced mRNA expression of CRH and RARα in the rat hypothalamus. In vitro, CRH expression decreased after ABA treatment across different neural cells. In BE(2)-C cells, ABA inhibited a series of retinoid receptor expression, including RARα, a receptor that could facilitate CRH expression directly.

Conclusions:

These results suggest that ABA may play a role in the pathogenesis of depression by downregulating CRH mRNA expression shared with the RA signaling pathway.     

Biosynthetic origin of the methoxyl extender unit in bafilomycin and concanamycin using stereospecifically labeled precursors

The microbial macrolides bafilomycin A1, B, and concanamycin A from Streptomyces spp. are potent and specific inhibitors of V-ATPases. The question of the biosynthetic origin of the two uncommon "glycolate units" of each of the macrolide structures was addressed by feeding experiments with stereospecifically 13C-labeled precursors. Our studies clearly indicate that glycerol is a source for the methoxylated C2-units and determines the orientation of the incorporation. Products from the carboxylic acid pool or TCA cycle are ruled out as key precursors. The data suggest the action of a glycerol kinase and point to phosphoglycerate as an intermediate in their biosynthesis. However, glycerate itself is not accepted as a precursor. We present the likely biosynthetic pathway and show the value of stereospecifically labeled presursors as an important tool for biosynthetic investigations.     

Antioxidant vitamins and risk of lung cancer

Tobacco use is the leading risk factor for lung cancer, yet in addition to smoking habit, diet may also play a role in the disease's appearance. While there are reports to indicate that antioxidant vitamins and carotenoids may decrease the risk of lung cancer, results to date have been somewhat ambiguous. This review aimed to describe the results yielded by different studies, which have addressed antioxidant vitamin intake and lung cancer, and to indicate the mechanisms whereby these nutrients might be exercising their activity. Antioxidant vitamins were observed to have no clear protective effect, though there was some evidence pointing to a protective role for vitamins C and E. Vitamin A, in contrast, evinced no clear effect. Insofar as provitamin A carotenoids were concerned, lutein/zeaxanthin, lycopene and alpha-carotene displayed a certain protective trend, yet beta-carotene exhibited no protective effect whatsoever; and indeed, there was speculation as to whether it might even be pernicious in smokers. Beta-criptoxanthin, on the other hand, showed a more consistent protective effect. The study highlighted the need to conduct further research on smokers and non-smokers alike, and in particular, to investigate the effect, if any, on lung cancer of carotenoids or vitamins when ingested in differing dosages.     

Biosynthesis of thiamin under anaerobic conditions in Saccharomyces cerevisiae

We studied the biosynthetic route of thiamin in Saccharomyces cerevisiae to see whether the route differed under aerobic and anaerobic conditions. Histidine and pyridoxine are the precursors of the pyrimidine moiety of thiamin under aerobic conditions. Formate is incorporated into the pyrimidine via histidine. The incorporation of [13C]formate and [5'-(2)H2]pyridoxine into the pyrimidine was examined under anaerobic conditions. The labels from [13C]formate and [5'-(2)H2]pyridoxine were not incorporated into the pyrimidine under anaerobic conditions, indicating that the biosynthetic pathway of the pyrimidine differed from that under aerobic conditions. On the other hand, [15N]glycine was incorporated into the thiazole under both anaerobic and aerobic conditions. The biosynthetic pathway of the thiazole was therefore unaltered by the O2 concentration.     

Evolutionary process of stress response systems controlled by abscisic acid in photosynthetic organisms

There are many serious problems causing a food crisis such as desertification, population explosion, and environmental destruction, suggesting that a severe food crisis will become reality across the globe. Therefore, the transgenic plants, which have tolerance to environmental stresses, may take on greater and greater importance in attempts to increase food production. Aquatic photosynthetic organisms, such as prokaryotic cyanobacteria and eukaryotic green algae, are considered as an evolutionary origin of higher plants and their basic metabolisms including photosynthesis are similar to higher plants. Thereby, stress responsive genes or reactions from these organisms may be exceedingly advantageous sources for creation of stress-tolerant transgenic plants. In this study, the physiological roles and biosynthesis of abscisic acid (ABA), well known as a signal molecule in the adaptation to environmental stresses, in microalgae were investigated from the point of the view of its functional evolution in the response to environmental stresses. Chlamydomonas reinhardtii, a green alga, and Synechocystis sp. PCC 6803, a cyanobacterium, were employed in this study as model organisms. It is expected that this comparative analysis will provide basic information for the creation of stress-tolerant transgenic plants. ABA may act in C. reinhardtii as a signal molecule to induce antioxidant reactions for elimination of reactive oxygen species, but not to induce specific response reactions to mitigate water stresses. In Synechocystis, on the other hand, exogenously added ABA did not influence the growth and gene expression. Moreover, ABA did not relieve growth suppression caused by water and oxidative stresses. From the carotenoid composition and bioinformatic analysis, it can be suggested that the ABA biosynthetic pathway generally found in higher plants exists completely in C. reinhardtii, but incompletely in Synechocystis.     

Strain improvement of recombinant Escherichia coli for efficient production of plant flavonoids

Plant flavonoid polyphenols continue to find increasing pharmaceutical and nutraceutical applications; however their isolation, especially of pure compounds, from plant material remains an underlying challenge. In the past Escherichia coli, one of the most well-characterized microorganisms, has been utilized as a recombinant host for protein expression and heterologous biosynthesis of small molecules. However, in many cases the expressed protein activities and biosynthetic efficiency are greatly limited by the host cellular properties, such as precursor and cofactor availability and protein or product tolerance. In the present work, we developed E. coli strains capable of high-level flavonoid synthesis through traditional metabolic engineering techniques. In addition to grafting the plant biosynthetic pathways, the methods included engineering of an alternative carbon assimilation pathway and the inhibition of competitive reaction pathways in order to increase intracellular flavonoid backbone precursors and cofactors. With this strategy, we report the production of plant-specific flavanones up to 700 mg/L and anthocyanins up to 113 mg/L from phenylpropanoic acid and flavan-3-ol precursors, respectively. These results demonstrated the efficient and scalable production of plant flavonoids from E. coli for pharmaceutical and nutraceutical applications.