提高衣康酸产量的代谢工程育种研究进展

衣康酸(itaconic acid,IA)是一种白色结晶状的不饱和二元羧酸,它是化学和制药工业中许多相关化合物的前体,被广泛应用于树脂、塑料、胶乳和超吸附剂等的工业生产中。与化学法生产衣康酸相比,生物法具有原料来源广泛,生产过程能耗低,不污染环境等优点。介绍了衣康酸合成的生物代谢途径,以及在野生型宿主和异源宿主中生产衣康酸和提高衣康酸产量的生物技术,为今后开展利用生物技术生产衣康酸的研究提供参考。     

生物可降解塑料的必酶生产研究进展

近十几年来,随着化学合成塑料造成环境污染的日趋严重,微生物合成生物可降解塑料的研究受到人们的广泛重视。聚羟基烷酸（ｐｏｌｙｈｙｄｒｏｘｙａｌｋａｎｏａｔｅｓ;ＰＨＡ）具有与化学合成塑料相似的性质,能拉丝、压模、注塑等,而且具有合成塑料所没有的特殊性能;如利用其生物相容性可作为外科手术缝线、人造血管和骨骼代用品,术后无需取出。因而在工业、农业、医药和环保等行业都具有广阔的应用前景。 目前,微生物发酵生产是获得生物可降解塑料的主要途径。对ＰＨＡ研究最多的是聚羟基丁酸（ｐｏｌｙ－３－ｈｙｄｒｏｘｙｂｕ…     

生物可降解塑料在不同环境条件下的降解研究进展北大核心CSCD

当前社会塑料制品的使用需求持续增加,塑料垃圾处理压力不断增大,减缓塑料污染成为当务之急,生物可降解塑料因可在一定生物活性环境下较快降解而备受关注,具有广阔的应用前景。生物可降解塑料降解条件复杂,影响因素众多,对不同生物可降解塑料降解规律,降解微生物和功能酶的透彻掌握,是实现其全面利用和高效资源化处理处置的基础和前提。文章系统梳理了常见生物可降解塑料的种类、性能、优缺点和主要用途,全面综述了生物可降解塑料的降解机理、降解微生物和功能酶,以及生物可降解塑料在不同环境条件下的降解周期和程度,以期为生物可降解塑料的微生物降解研究提供借鉴,为生物可降解塑料废弃物的高效处理处置和彻底降解提供科学参考。     

生物可降解塑料的发酵生产研究进展*

近十几年来,随着化学合成塑料造成环境污染的日趋严重,微生物合成生物可降解塑料的研究受到人们的广泛重视.聚羟基烷酸(polyhydroxyalkanoates,PHA)具有与化学合成塑料相似的性质,能拉丝、压模、注塑等,而且具有合成塑料所没有的特殊性能,如利用其生物相容性可作为外科手术缝线、人造血管和骨骼代用品,术后无需取出.因而在工业、农业、医药和环保等行业都具有广阔的应用前景.     

嗜盐菌生物合成聚羟基脂肪酸酯(PHAs)的研究进展

微生物体内积累的聚羟基脂肪酸酯(PHAs)是一种可降解的生物塑料,利用微生物合成绿色环保的PHAs替代石化塑料可减少白色污染。嗜盐菌合成PHA可省略繁琐的灭菌和无菌条件培养的苛刻条件,较其他微生物更具有经济效益和竞争性。结合目前国内外嗜盐菌合成PHA的研究进展,对嗜盐菌合成的PHA进行分类,并对由嗜盐菌合成PHA的影响因素进行总结分析。同时,对嗜盐菌合成PHA的发展前景进行了展望。     

真菌草酸的代谢和作用研究进展

草酸(oxalic acid)是一种重要的生物代谢产物,广泛分布于植物、动物和微生物中,在不同的生命体中发挥重要功能.本文回顾了国内外关于真菌草酸的相关研究进展.许多真菌能够分泌草酸,包括植物病原真菌、食药用真菌及工业真菌等.草酸作为一种简单的二元羧酸,在真菌中主要通过三羧酸循环途径、乙醛酸循环途径和草酰乙酸途径合成....     

微生物发酵琥珀酸的研究进展

琥珀酸是一种重要的C_4平台化合物,生物基琥珀酸可作为合成大宗化学品的起始原料,在食品、医药、表面活性剂、洗涤剂、绿色溶剂、生物可降解塑料和动植物生长刺激物剂领域有广泛的应用前景。从可再生原料出发,发酵过程固定CO_2,使得微生物发酵生产琥珀酸具有良好的环境优势,成为近年研究的热点。围绕微生物发酵法生产琥珀酸迫切需要解决的主要问题,综述了国内外对琥珀酸生产菌的选育、其代谢机理与产酸条件、发酵过程工艺、产品提取等方面的研究现状。     

利用生物基原料合成聚羟基脂肪酸酯

聚羟基脂肪酸脂(polyhydroxyalkanoates,PHA)是细菌胞内的一类具有相似结构的碳源和能源的储备物,由于它的力学性能与某些热塑性材料聚乙烯、聚丙烯类似,并且可以完全降解进入自然界的生态循环,因而被认为是一种"生物可降解塑料",有可能替代传统的、不可降解的、由石油产品合成的塑料,而受到世界各国的重视.     

生产聚羟基脂肪酸酯的微生物细胞工厂

聚羟基脂肪酸酯(PHA)是一类由微生物合成的、生物可再生、生物可降解、具有多种材料学性能的高分子聚合物,在很多领域有着广泛的应用前景。以下从辅酶工程、代谢工程、微氧生产等方面综述了微生物法生产PHA的研究进展,并对利用PHA合成基因提高基因工程菌的代谢潜能进行了讨论。     

信息库

信息库１．在气升式生物反应器中用玉米淀粉培养米根霉提高Ｌ（＋）┐乳酸的产量由乳酸合成的聚乳酸（ＰＬＡ）是制造生物可降解塑料最可取的一种材料。然而ＰＬＡ能否在价格上与石油化工业生产的聚乙烯（每公斤约１．５美元）竞争是其中最大的难题。通常乳酸生产是用乳酸...     

Four-carbon dicarboxylic acid production through the reductive branch of the open cyanobacterial tricarboxylic acid cycle in Synechocystis sp. PCC 6803

Succinate, fumarate, and malate are valuable four-carbon (C4) dicarboxylic acids used for producing plastics and food additives. C4 dicarboxylic acid is biologically produced by heterotrophic organisms. However, current biological production requires organic carbon sources that compete with food uses. Herein, we report C4 dicarboxylic acid production from CO₂ using metabolically engineered Synechocystis sp. PCC 6803. Overexpression of citH, encoding malate dehydrogenase (MDH), resulted in the enhanced production of succinate, fumarate, and malate. citH overexpression increased the reductive branch of the open cyanobacterial tricarboxylic acid (TCA) cycle flux. Furthermore, product stripping by medium exchanges increased the C4 dicarboxylic acid levels; product inhibition and acidification of the media were the limiting factors for succinate production. Our results demonstrate that MDH is a key regulator that activates the reductive branch of the open cyanobacterial TCA cycle. The study findings suggest that cyanobacteria can act as a biocatalyst for converting CO₂ to carboxylic acids.     

Factors contributing to the inhibition of aspartate aminotransferase by dicarboxylic acids.

At pH 8.0 aspartate aminotransferase (L-aspartate:2-oxoglutarate aminotransferase, EC 2.6.1.1) reacts with the modified substrate, erythro-beta-hydroxy-L-aspartate, to form a mixture of enzyme-substrate complexes absorbing at 492 nm. A variety of dicarboxylic acids were studied spectrophotometrically as competitive inhibitors of this reaction. All of the inhibitory dicarboxylic acids form a complex with the enzyme, absorbing at 362 nm. In addition, some of the dicarboxylic acids form a protonated complex absorbing at about 435 nm. This complex, which is the conjugate acid of that absorbing at 362 nm, is formed only by those dicarboxylic acids which can assume a configuration in which the two carboxyl groups are positioned as in maleic acid. Bulky substituents, such as aromatic rings or even methyl groups, prevent the formation of the protonated complex, presumably because of steric restrictions at the active site. Substitution of the central carbon atom of glutaric acid by heteroatoms of increasing charge density results in a progressive decrease in inhibitory effectiveness, at pH 8, primarily due to a loss of this pH-dependent stabilization of the enzyme-dicarboxylic acid complex. Acids with an aromatic ring are among the most potent dicarboxylic acid inhibitors of this enzyme in spite of the fact that they do not undergo the pH-dependent stabilization of their enzyme complexes. From these observations it was concluded that the affinity of aspartate aminotransferase for dicarboxylic acids is determined as much by the mechanism of binding as by the solvation and steric effects.     

In silico screening of dicarboxylic acids for cocrystallization with phenylpiperazine derivatives based on both cocrystallization propensity and solubility advantage

In silico screening was performed to search for binary solids in which a phenylpiperazine-derivative drug was cocrystallized with a dicarboxylic acid. The phenylpiperazine derivative could be any of 61 such drugs, while the dicarboxylic acid could be any of nine such acids. The uniqueness of this approach was that two criteria had to be fulfilled simultaneously, namely a high propensity for cocrystallization and a sufficient solubility advantage. Using the mixing enthalpies of selected pairs of crystal formers with high affinities for one another permitted the classification of candidates with a high probability of cocrystallization. Further modeling of the solubility advantage allowed the identification of many binary solids that potentially exhibit significantly enhanced solubility in water. Based on the computed values for the mixing enthalpies and solubility advantage factors, it was concluded that dicarboxylic acids are both excellent coformers for cocrystallization with phenylpiperazines and very good solubility enhancers; indeed, the use of dicarboxylic acids as coformers would allow the degree of dissolution to be tuned for many of the studied drugs. The observed similarities of the cocrystallization landscapes of the studied drugs and excipients were also explored.     

Unusual carbon fixation gives rise to diverse polyketide extender units

Polyketides are structurally diverse and medically important natural products that have various biological activities. During biosynthesis, chain elongation uses activated dicarboxylic acid building blocks, and their availability therefore limits side chain variation in polyketides. Recently, the crotonyl-CoA carboxylase-reductase (CCR) class of enzymes was identified in primary metabolism and was found to be involved in extender-unit biosynthesis of polyketides. These enzymes are, in theory, capable of forming dicarboxylic acids that show any side chain from the respective unsaturated fatty acid precursor. To our knowledge, we here report the first crystal structure of a CCR, the hexylmalonyl-CoA synthase from Streptomyces sp. JS360, in complex with its substrate. Structural analysis and biochemical characterization of the enzyme, including active site mutations, are reported. Our analysis reveals how primary metabolic CCRs can evolve to produce various dicarboxylic acid building blocks, setting the stage to use CCRs for the production of unique extender units and, consequently, altered polyketides.     

己二酸的生物合成

己二酸是六碳二元羧酸,主要用于生产尼龙、化纤和工程塑料等聚合物,年需求量近300万吨。目前己二酸的工业生产主要是利用硝酸氧化芳烃合成己二酸等化学法获得,不仅污染严重,而且是个不可持续的过程,需要发展可行的替代合成方法。近年来,随着合成生物学和代谢工程的发展,绿色、洁净的己二酸生物合成方法逐渐受到人们的关注和重视。文中就己二酸及其前体物的生物合成研究进展进行了综述,并对可能的合成新途径做了展望。     

Utilization of 3-hydroxybutyrate by chick cerebral hemispheres during postnatal maturation.

1. The utilization of 3-hydroxybutyrate has been studied in the chick telencephalon during its post-hatching maturation. 2. In the 1-day-old chick the blood concentration of 3-hydroxybutyrate appears to be relatively high and its value is 5 times that estimated in the 4- and 30-day-old chicks. 3. The determination of the cerebral arteriovenous differences of 3-hydroxybutyrate shows that the brain of the newly-hatched chick takes up 3 times more actively this ketone body than the brain of the 4-day-old bird does. 4. During incubation in a non-oxygenated and an oxygenated physiological medium, in the presence of 3-hydroxy [3-14C]butyrate, the specific radioactivity of the dicarboxylic amino acids in the 1-day-old chick brain slices is higher than in those of the 30-day-old chick, particularly in the oxygenated medium. 5. Thirty minutes after a subcutaneous injection of 3-hydroxy [3-14C]butyrate, the specific radioactivity of the dicarboxylic amino acids in the 1-day-old chick telencephalon is 3-4 times higher than that in the 4- and 30-day-old chick. 6. In conclusion, in the brain of the newly hatched chick, 3-hydroxybutyrate is an efficient precursor in the biosynthesis of dicarboxylic amino acids, particularly glutamate, and, as glucose, it is metabolically related to the "large compartment" of glutamate. 7. These results have been discussed comparatively to those previously obtained in the developing rodent brain.     

The microsomal dicarboxylyl-CoA synthetase.

Dicarboxylic acids are products of the omega-oxidation of monocarboxylic acids. We demonstrate that in rat liver dicarboxylic acids (C5-C16) can be converted into their CoA esters by a dicarboxylyl-CoA synthetase. During this activation ATP, which cannot be replaced by GTP, is converted into AMP and PPi, both acting as feedback inhibitors of the reaction. Thermolabile at 37 degrees C, and optimally active at pH 6.5, dicarboxylyl-CoA synthetase displays the highest activity on dodecanedioic acid (2 micromol/min per g of liver). Cell-fractionation studies indicate that this enzyme belongs to the hepatic microsomal fraction. Investigations about the fate of dicarboxylyl-CoA esters disclosed the existence of an oxidase, which could be measured by monitoring the production of H2O2. In our assay conditions this H2O2 production is dependent on and closely follows the CoA consumption. It appears that the chain-length specificity of the handling of dicarboxylic acids by this catabolic pathway (activation to acyl-CoA and oxidation with H2O2 production) parallels the pattern of the degradation of exogenous dicarboxylic acids in vivo.     

Gas chromatography-mass spectrometry profile of urinary organic acids of Wistar rats orally treated with ozonized unsaturated triglycerides and ozonized sunflower oil

The main products in the ozonolysis of unsaturated triglycerides or vegetable oils are peroxides, aldehydes, Criegee ozonides and carboxylic acids. Some of these compounds are present in different concentrations in the biological fluids. The aim of this work is to study, using gas chromatography-mass spectrometry (GC-MS), the organic acid excretion in urine of rats orally treated with ozonized sunflower oil (OSO), ozonized triolein or ozonized trilinolein. Oral administration of OSO to Wistar rats has produced changes in the urinary content of dicarboxylic organic acids. Among others heptanedioic (pimelic acid) and nonanedioic acids (azelaic acid) were the major increased dicarboxylic acids found. The urinary dicarboxylic acid profiles of rats which received ozonized triolein only showed an increase in heptanedioic and nonanedioic acids. However, when ozonized trilinolein is applied, the profile is similar to that obtained when OSO is administered. A biochemical mechanism is proposed to explain the formation of dicarboxylic acids from ozonated unsaturated triglycerides.     

Metabolic origin of urinary 3-hydroxy dicarboxylic acids

3-Hydroxy dicarboxylic acids with chain lengths ranging from 6 to 14 carbons are excreted in human urine. The urinary excretion of these acids is increased in conditions of increased mobilization of fatty acids or inhibited fatty acid oxidation. Similar urinary profiles of 3-hydroxy dicarboxylic acids were also observed in fasting rats. The metabolic genesis of these urinary 3-hydroxy dicarboxylic acids was investigated in vitro with rat liver postmitochondrial and mitochondrial fractions. 3-Hydroxy monocarboxylic acids ranging from 3-hydroxyhexanoic acid to 3-hydroxyhexadecanoic acid were synthesized. In the rat liver postmitochondrial fraction fortified with NADPH, these 3-hydroxy fatty acids with carbon chains equal to or longer than 10 were oxidized to (omega - 1)- and omega-hydroxy metabolites as well as to the corresponding 3-hydroxy dicarboxylic acids. 3-Hydroxyhexanoic (3OHMC6) and 3-hydroxyoctanoic (3OHMC8) acids were not metabolized. Upon the addition of mitochondria together with ATP, CoA, carnitine, and MgCl2, the 3-hydroxy dicarboxylic acids were converted to 3-hydroxyoctanedioic, trans-2-hexenedioic, suberic, and adipic acids. In the urine of children with elevated 3-hydroxy dicarboxylic acid levels, 3OHMC6, 3OHMC8, 3-hydroxydecanoic, 3,10-dihydroxydecanoic, 3,9-dihydroxydecanoic, and 3,11-dihydroxydodecanoic acids were identified. On the basis of these data, we propose that the urinary 3-hydroxy dicarboxylic acids are derived from the omega-oxidation of 3-hydroxy fatty acids and the subsequent beta-oxidation of longer chain 3-hydroxy dicarboxylic acids. These urinary 3-hydroxy dicarboxylic acids are not derived from the beta-oxidation of unsubstituted dicarboxylic acids.