Structure-activity Relationship of Herbicidal 2,3-Dicyano-5-Substituted Pyrazines

Sixty six 2,3-dicyano-5-substituted pyrazines were synthesized and their herbicidal activities against barnyard grass were measured in pot tests to clarify the relationship between chemical structure and activity. The activity of 59 derivatives was related parabolically to the hydrophobic substituent parameter at the 5-position of the pyrazine ring.     

Immobilization of levan fructotransferase for the production of di-fructose anhydride from levan

Levan fructotransferase (LFTase) from Arthrobacter ureafaciens K2032 was immobilized on various carriers of which Chitopearl BCW2501 beads showed the higher activity of 320 U g^–1 for the formation of di-fructose anhydride compounds. The immobilized enzyme retained about 60% of its initial activity after being used for 20 cycles.     

Levan果聚糖的应用与生产研究进展

Levan是一类果聚糖,由大量的果糖单元以β-（2,6）果糖苷键连接构成聚糖主链并含有少量β-（2,1）果糖苷键连接的支链组成。部分微生物来源的Levan具有抗肿瘤、抗病毒、降血糖、降血脂、免疫增强等重要的生物活性,在医药和功能性食品方面具有巨大的应用潜能。微生物发酵液提取和酶法合成是目前大量获得Levan果聚糖的两种方法,其中微生物发酵液提取的Levan果聚糖产量和蔗糖转化率一般较低,且发酵液中同时存在的其他高聚物不利于Levan的规模化纯化;而利用Levan蔗糖酶以蔗糖为底物转果糖基合成的Levan果聚糖产量已经高达200g/L、蔗糖转化率高达50%,并且Levan蔗糖酶合成Levan过程中酶的活性受到pH值、温度、螯合剂、金属离子等多种因素的影响,可以通过控制反应条件促进多糖合成反应的进行。因此,酶法合成将是工业化获得Levan果聚糖的主要方式。     

Disruption of the Zymomonas mobilis extracellular sucrase gene (sacC) improves levan production

AIMS: Disruption of the extracellular Zymomonas mobilis sucrase gene (sacC) to improve levan production. METHODS AND RESULTS: A PCR-amplified tetracycline resistance cassette was inserted within the cloned sacC gene in pZS2811. The recombinant construct was transferred to Z. mobilis by electroporation. The Z. mobilis sacC gene, encoding an efficient extracellular sucrase, was inactivated. A sacC defective mutant of Z. mobilis, which resulted from homologous recombination, was selected and the sacC gene disruption was confirmed by PCR. Fermentation trials with this mutant were conducted, and levansucrase activity and levan production were measured. In sucrose medium, the sacC mutant strain produced threefold higher levansucrase (SacB) than the parent strain. This resulted in higher levels of levan production, whilst ethanol production was considerably decreased. CONCLUSIONS: Zymomonas mobilis sacC gene encoding an extracellular sucrase was inactivated by gene disruption. This sacC mutant strain produced higher level of levan in sucrose medium because of the improved levansucrase (SacB) than the parent strain. SIGNIFICANCE AND IMPACT OF THE STUDY: The Z. mobilis CT2, sacC mutant produces high level of levansucrase (SacB) and can be used for the production of levan.     

Fructans in crested wheatgrass leaves

Crested wheatgrass is an important cool-season grass that has become naturalized in many semiarid regions of the western U.S. It provides ground cover and reduces soil erosion caused by water and wind. Additionally, crested wheatgrass produces important forage for livestock and wildlife on 6 to 8 million hectars of western rangeland. It is well adapted to semiarid cold desert regions because of its cool temperature growth and drought tolerance. Understanding the biosynthesis of fructans in crested wheatgrass is important because of their likely role in both cool temperature growth and drought tolerance. Recent research described a major gene (6-SFT) in crested wheatgrass that is involved in fructan biosynthesis. 1-kestotriose, the major DP3 fructan in crested wheatgrass, serves as the substrate for the two major DP4 fructans, 1&6-kestotetraose and 1,1-kestotetraose. The three major DP5 fructans are 1&6,1-kestopentaose, 1,1&6-kestopentaose and 1,1,1-kestopentaose. The major DP6 fructan is 1&6, 1&6-kestohexaose. We postulate that 1&6,1&6-kestohexaose is synthesized from the addition of a fructose to 1&6, 1-kestopentaose. This paper provides structures of the various DP 3, 4, 5 and 6 fructan types produced by crested wheatgrass and provides suggested biosynthetic pathways for all major fructan linkage types present.     

Partial characterization of levan polymer from Pseudomonas fluorescens with significant cytotoxic and antioxidant activity

Microbial levan has great potential as a functional biopolymer in different fields including foods, feeds, cosmetics, and the pharmaceutical and chemical industries. In this study, a good levan producer bacterial strain of Pseudomonas fluorescens strain ES, isolated from soil in Egypt in a previous study, was used. Levan production by this strain was optimized using Plackett-Burman experimental design (PBD) to screen the critical factors of several process variables and Centered Central Composite Design (CCD) was applied for further estimation of the relationship between the variables and the response as well as optimization of the levels. Plackett-Burman (P-B) design showed a p-value 0.0144 less than 0.05 indicated the significance of the model. Sucrose, potassium dihydrogen phosphate, yeast extract and pH value showed the most significant effect on levan concentration at the values of 89.17, 65.83, 24.17, and 15.83, respectively. The purified levan polymer was characterized using different Physico-chemical methods such as Fourier Transform Infrared Spectrometer (FTIR), Nuclear magnetic resonance (NMR), and High-Performance Liquid Chromatography (HPLC) to determine the main composition and functional groups in the obtained polymer. HPLC results indicated that the polymer purification increased the percentage of fructose residue from 75 up to 89. Furthermore, ¹H and ¹³C NMR spectroscopy analysis showed great matching between the obtained signal for our polymer with that reported in other people^’s work. The obtained levan polymer exhibited cytotoxic activity against Human epidermoid Skin carcinoma and Hepatocellular carcinoma with IC50 of 469 and 222.7 µg/ml, respectively. Antioxidant activity was determined using DPPH assay and the percentage of inhibition at 1000 µg/ml was found to be <50 (13.89 ± 1.07) with IC50 of (24.42 ± 0.87).     

Unraveling the role of flexible coil near calcium binding site of levansucrase on thermostability and product profile via proline substitution and molecular dynamics simulations

Due to its bioactivity and versatile applications, levan has appeared as a promising biomaterial. Levansucrase is responsible for the conversion of sucrose into levan. With the goal of enhancing levan production, the strategy for enhancing the stability of levansucrase is being intensively studied. To make proteins more stable under high temperatures, proline, the most rigid residue, can be introduced into previously flexible regions. Herein, G249, D250, N251, and H252 on the flexible coil close to the calcium binding site of Bacillus licheniformis levansucrase were replaced with proline. Mutations at G249P greatly enhance both the enzyme's thermodynamic and kinetic stability, while those at H252P improve solely the enzyme's kinetic stability. GPC analysis revealed that G249P synthesize more levan, but H252P generate primarily oligosaccharides. Molecular dynamics simulations (MD) and MM/GBSA analysis revealed that G249P mutation increased not only the stability of levansucrase, but also affinity toward fructan.     

Changes of Casein Complex during Storage of Sterilized Skim Milk

Two types of sterilized skim milk were prepared; one was HTS–1 milk which was heated at 130°C flashly and the other was HTS–2 milk which was heated at 130~135°C for 75 sec. The changes of casein complex during storage of HTS–1 and HTS–2 milks were examined and compared with those of AUT milk which was heated at 120°C for 15 min. The results obtained are summarized as follows.

(1) Visible sediment was formed in HTS–1 and HTS–2 milks after 8 and 14 months of storage, respectively, while no sediment was observed in AUT miik throughout 15 months of storage. (2) The amount of calcium in the ultracentrifugal wheys of HTS–1 and HTS–2 milks decreased gradually with prolonged storage, while that in the ultracentrifugal whey of AUT milk was kept constant after 1 month of storage. (3) Almost no differences among the three samples were observed in the increments of Ca/N ratio of ultracentrifuged casein complex during storage. (4) The amount of soluble casein increased in AUT milk during storage, but decreased in HTS–1 and HTS–2 milks.

On the basis of the above results, the destabilization of casein complex during storage was discussed.     

Simultaneous and selective production of levan and poly(γ-glutamic acid) by <Emphasis Type="Italic">Bacillus subtilis</Emphasis>

Bacillus subtilis(natto) Takahashi, used to prepare the fermented soybean product natto, was grown in a basal medium containing 5% (w/w) sucrose and 1.5% (w/w) l-glutamate and produced 58% (w/w) poly(-glutamic acid) and 42% (w/w) levan simultaneously. After 21 h, 40–50 mg levan ml^-1had been produced in medium containing 20% (w/w) sucrose but without l-glutamate. In medium containing l-glutamic acid but without sucrose, mainly poly(-glutamic acid) was produced. Revisions requested 28 August 2004/14 October 2004; Revisions received 11 October 2004/22 November 2004