真菌中麦角甾醇合成的调控机制

对细胞中麦角甾醇合成的调控是维持真菌细胞中甾醇含量的关键,文中综述了真菌中麦角甾醇合成的途径,并对其调控机理的研究进展作了重点介绍。甾醇调控元件结合蛋白(SREBP)是真菌中保守的甾醇合成调控因子,能够通过响应麦角甾醇含量的变化来调控甾醇合成基因的表达。但SREBP系统在不同真菌中发生了进化,在酵母亚门中,转录因子Upc2p替代了SREBP,成为了最主要的甾醇合成调控因子。此外,甾醇中间代谢物也被证明可以诱导麦角甾醇合成基因的表达,预示着真菌中存在更为精细的调控机制。     

微波法提取菱角中甾醇类化合物的研究

本文研究了微波法提取菱角中甾醇类化合物的新方法。通过正交实验确定了甾醇的最佳提取条件为：95％乙醇作提取剂,微波功率420W,料液比1：5,提取时间60s,提取2次。以紫外分光光度法测定了样品中植物总甾醇的含量,其中菱角皮中含总甾醇0．624mg,／g,菱角仁中含总甾醇0．640mg／g。该方法的平均回收率为91．6％。与超声波法及索氏回流法相比,微波法提取菱角中甾醇类化合物的提取时间极短,由3～6h减少为60s,而提取效率却提高了1／3左右。从节能、技术经济和资源综合利用的角度来看,微波法将有广阔的应用前景。     

植物甾醇酯合成研究进展

植物甾醇广泛存在于植物的根、茎、叶、果实和种子中,易受光、热、氧化等作用而被分解,具有生物利用率低、水溶性和脂溶性较差等特点。植物甾醇与脂肪酸酯化生成的植物甾醇酯可以有效降低植物甾醇的氧化率,具有更好的脂溶性和降血清、胆固醇的能力,更易被人体吸收。作为一类新型的功能食品添加剂,植物甾醇酯的市场需求量逐年增长。对植物甾醇酯的原料植物甾醇和脂肪酸来源进行了简单介绍,就近年来国内外植物甾醇酯的合成方法进行了系统阐述,重点介绍了酸/碱化学催化法和脂肪酶催化合成方法,对这两类方法的优缺点分别进行了评价,并对未来研究的重点内容和待突破的核心技术进行了展望。     

豆甾醇与琥珀酸酐单酯化反应工艺及动力学研究

研究了甲苯为溶剂,吡啶为催化剂,豆甾醇与琥珀酸酐的酯化反应工艺和反应动力学。探讨了反应温度、催化剂吡啶用量、反应物的摩尔配比和反应时间对酯化反应结果的影响。实验结果表明:豆甾醇与琥珀酸酐的反应产物为豆甾醇琥珀酸单酯;当吡啶的体积分数为1.5%,反应物的摩尔比为1.0∶1.6,回流下反应20 h后,豆甾醇的酯化率大于97%,反应后的溶液经蒸发回收溶剂甲苯,固体产物分别经乙醇和水洗涤除杂,所得固体在60℃下真空干燥至恒重,得到的豆甾醇琥珀酸单酯的单程收率大于86%。单酯化反应满足二级不可逆反应动力学规律,反应的活化能为85 kJ/mol。     

生长素与油菜素甾醇相互作用机制的研究进展

植物生长发育是一个复杂、精细的调控过程,涉及细胞、组织和器官间多层次的信息交流,激素在其间发挥了重要调控作用．生长素和油菜素甾醇（BR）都能促进植物伸长,随着对其作用机制研究的深入,人们发现它们协同调控很多生理过程,对二者作用机制和信号转导的相互作用研究也成为激素研究领域的热点之一．对生长素和BR转导途径的揭示及直接下游基因的大规模发掘为二者通过相互作用调控不同生理过程的机制研究提供了重要线索．生长素和BR的相互作用涉及到下游基因转录的调控、信号组分互作以及合成代谢和极性运输等多层次的调控．     

油菜素类甾醇的存在、生理活性、构效关系及其它

油菜素类甾醇是近年来人们首次从植物中发现并分离到的一种具生理活性的甾体类植物生长激素。由于它具有较高生理活性,且实验证明它能使水稻等农作物及蔬菜增产,是一种很有应用价值的植物生长激素,因而近年来对它的研究日渐增多。本文就油菜素类甾醇的存在、生理活性及构效关系等进行了较为系统、全面的综述。     

酵母甾醇转运蛋白研究进展

甾醇是一类广泛存在于生物体内的环戊烷骈多氢菲衍生物,其不仅是细胞膜的重要组成成分,还具有重要的生理和药理活性。随着合成生物学和代谢工程技术的发展,近些年来应用酵母细胞异源合成甾醇的研究不断深入。但由于甾醇是疏水性大分子,倾向于积累在酵母的膜结构中而引发细胞毒性,一定程度上限制了甾醇产量的进一步提升。因此,揭示酵母中甾醇转运机制,特别是与甾醇转运相关的转运蛋白的工作原理,有助于设计新的策略,解除酵母细胞工厂中的甾醇积累毒性、实现甾醇增产。酵母中甾醇转运主要通过蛋白质介导的非囊泡运输机制来完成,本文归纳了酵母中已报道的5类甾醇转运相关蛋白,即OSBP/ORPs家族蛋白、LAM家族蛋白、NPC样甾醇转运蛋白、ABC转运家族蛋白和CAP超家族蛋白,汇总了这些蛋白对细胞内甾醇梯度分布和稳态维持所起的重要作用。此外,本文还综述了甾醇转运蛋白在酵母细胞工厂中的应用现状。     

植物体内甾醇的合成和生理作用

植物甾醇属于甾类化合物,以自由状态,与复杂脂类或和某些化合物结合成复合体的形式,存在于高等植物的细胞膜,细胞质和细胞器内,细胞膜内的甾醇和磷脂相互作用能够保持膜结构的稳定和调节细胞膜透性。植物体内甾醇的合成是从乙酰辅酶A（acetyl-CoA)开始,并有其种类特异性和特有的酶催化系统。甾醇参与植物对外界的胁迫反应,因此,获得甾醇突变体植株是抗病虫育种的有效途径。     

新疆蓝刺头化学成分研究

以新疆蓝刺头(Echinops ritro L.)全草为研究材料,通过硅胶柱色谱,Sephadex LH-20柱色谱,重结晶等技术对新疆蓝刺头化学成分进行分离纯化,通过理化性质分析及1H-NMR,13C-NMR等技术对化合物结构进行鉴定.结果表明,共分离出5个化合物,分别是三萜类化合物蒲公英甾醇乙酰酯(化合物1)、蒲公英甾醇(化合物2)、黄酮苷类化合物金丝桃苷(化合物3)、胡萝卜苷(化合物4)与β-豆甾醇葡萄糖苷(化合物5).其中化合物1,2,5首次从该种植物中分离,化合物3为首次从该属植物中分离.     

油菜甾醇内酯类化合物结构与活性的相关性

比较了19种油菜甾醇内酯类似物和有关甾体化合物在水稻叶片倾斜及萝卜幼苗生长试验中的生物活性。表油菜甾醇内酯(24—Epi—BR)在两个系统中都具有很强的生物活性。C_2位失去羟基(香蒲甾醇)仅在水稻试验中有高活性,改变C_22位侧链结构(2α,3α双羟基—6—酮—23,24—双失碳—β—高-5α—胆烷酸甲酯)在萝卜试验中仍有活性。     

Free and bound sterols in seedlings of Cucumis sativus

Free sterols, sterol esters, sterol monoglucosides and sterol acylmonoglucosides have been obtained from 10 days old seedlings of Cucumis sativus. Free sterols and sterol esters consist mainly of Δ⁷ di- and triunsaturated sterols, whereas Δ⁷ mono-unsaturated and Δ⁵ mono- and diunsaturated sterols predominate in the glucosides and acylglucosides. Both acetates and derivatives of higher fatty acids, mainly linoleic and linolenic acids, have been found in the sterol esters. Sterol acylglucosides contain mostly saturated fatty acids, palmitic and stearic acids being the main components.     

Sterols of the Green‐Pigmented,Freshwater Raphidophyte,Gonyostomum semen,from Scandinavian Lakes

Sterols are a class of membrane‐reinforcing, ringed lipids which have a long history of examination in algae as a means of deriving chemotaxonomic relationships and as potential lipidic biomarkers. The Raphidophyceae represent a class of harmful, bloom‐forming, marine and freshwater algae. To date, there have been four published examinations of their sterol composition, focusing primarily on brown‐pigmented, marine species within the genera, Chattonella, Fibrocapsa, and Heterosigma. Lacking in these examinations has been the species Gonyostomum semen Ehrenb., which is a green‐pigmented, freshwater raphidophyte with a worldwide distribution. The goal of this study was to examine the sterol composition of this nuisance alga, determine the potential of using its sterol profile as a biomarker, and finally to determine if there is any intraspecific variability between isolates. We have examined 21 isolates of G. semen from a number of Scandinavian lakes, and all were found to produce two major sterols, 24‐ethylcholesta‐5,22E‐dien‐3β‐ol and 24‐ethylcholest‐5‐en‐3β‐ol, and 24‐methylcholest‐5‐en‐3β‐ol as a minor sterol; the presence of 24‐ethylcholesta‐5,22E‐dien‐3β‐ol differentiates G. semen from brown‐pigmented, marine raphidophytes which generally lack it. The results of this study indicate that isolates of G. semen from geographically separate lakes across Finland and Scandinavia have the same sterol biosynthetic pathway, and that there is no evolutionary divergence between the isolates with regard to sterol composition. The sterols of G. semen are not considered to be useful biomarkers for this particular organism because they are commonly found in other algae and plants.     

Is Pneumocystis a Plant?

Pneumocystis, an AIDS-associated opportunistic pathogen of the lung has some unusual features. This article focuses on work done by my group to understand the organism's distinct sterols. Although Pneumocystis is closely related to fungi, it lacks the major fungal sterol, ergosterol. Several delta(7) 24-alkysterols synthesized by P. carinii are the same as those reported in some basidiomycete rust fungi. The 24-alkylsterols are synthesized by the action of S-adenosyl-L-methionine:C-24 sterol methyl transferase (SAM:SMT). Fungal SAM:SMT enzymes normally transfer only one methyl group to the C-24 position of the sterol side chain and the cells accumulate C28 24-alkylsterols. In contrast, the P. carinii SAM:SMT and those of some plants catalyze one or two methyl transfer reactions producing both C28 and C29 24-alkylsterols. However, unlike most fungi, plants, and the kinetoplastid flagellates Leishmania and Trypanosoma cruzi, P. carinii does not appear to form double bonds at C-5 of the sterol nucleus and C-22 of the sterol side chain. Furthermore, the P. carinii SAM:SMT substrate preference for C30 lanosterol differs from that of homologous enzymes in any other organisms studied. C31 24-Methylenelanosterol and C32 pneumocysterol, products of SAM:SMT activity on lanosterol, can accumulate in high amounts in some, but not all, human-derived Pneumocystis jiroveci populations.     

Sterols and their transport in animal development

The cellular content of different sterols in invertebrates and vertebrates as well as their origin (endogenous and food sources) and significance for the life cycle are comparatively reviewed. The initial signaling role of sterols in the vital activity (in all multicellular animals) and later obligatory incorporation of certain sterols in cell membranes as a plastic components (in vertebrates) are proposed based on the presented data.     

Sterol-binding polysaccharides of Rhizopus arrhizus, Penicillium roquefortii and Saccharomyces carlsbergensis

Polysaccharides that bind with sterols and render them water-soluble were isolated from two mycelial fungi, Rhizopus arrhizus and Penicillium roquefortii and a yeast Saccharomyces carlsbergensis. The polysaccharides from R. arrhizus and S. carlsbergensis were accompanied by small quantities of phosphorus, protein and lipid, none of which significantly influenced the binding of sterol to polysaccharide. The chemical composition and sterol-binding properties of the polysaccharides from the filamentous species were almost identical, but differed significantly from those of the yeast polysaccharide. The principal sterol-binding polysaccharide of S. carlsbergensis was identified as a mannan and that of the filamentous fungi as a glucan(s). The binding capacity of the purified yeast polysaccharide was almost two-fold greater than that of R. arrhizus and P. roquefortii.     

Biosynthesis of sterol esters in Phycomyces blakesleeanus

A cell-free enzyme preparation of P. blakesleeanus has been shown to possess phosphatidylcholine: sterol acyltransferase, sterol ester hydrolase an     

Sterol methenyl transferase inhibitors alter the ultrastructure and function of the Leishmania amazonensis mitochondrion leading to potent growth inhibition

We describe here the effects of Delta(24(25)) sterol methenyl transferase inhibitors (SMTI) on promastigote and axenic amastigote forms of Leishmania amazonensis. When these cells were exposed to 20-piperidin-2-yl-5alpha-pregnan-3beta-20-diol (22,26-azasterol; AZA), hydrazone-imidazol-2-yl-5alpha-pregnan-3beta-ol (IMI), 20-hydrazone-pyridin-2-yl-5alpha-pregnan-3beta-ol (PYR) or 24(R,S),25-epiiminolanosterol (EIL), a concentration- and time-dependent inhibition of growth was observed, with IC(50) values in the sub-micromolar range. Ultrastructural alterations in treated cells were mainly observed in the mitochondrion, which displayed an intense swelling and a reduction of the electron density of the matrix with remarkable changes in the inner mitochondrial membranes. Mitochondrial transmembrane electric potential (DeltaPsi) was measured using spectrophotometric methods in control and treated promastigotes permeabilized with digitonin. After energization with the substrates for complexes I, II or IV of the respiratory chain, it was possible to detect marked changes of DeltaPsi in promastigotes treated with 1 microM of the SMTI for 48 or 72 h when compared with normal cells, indicating that these compounds led to the loss of the energy-transducing properties of the mitochondrial inner membrane, probably related to the alteration of its lipid composition. The present study confirms these findings, showing that in Leishmania amazonensis the mitochondrial complex appears to be the first organelle affected after treatment with different SMTI.     

Lipid changes in tobacco cell suspensions following treatment with cellulase elicitor

Tobacco ( Nicotians tabacum ) KY14 cell cultures have previously been reported to produce capsidiol and other stress metabolites when treated with fungal elicitor or cellulase. Using a new high performance liquid chromatographic technique, we have measured the changes in sesquiterpene phytoalexins and membrane lipid classes thai occur upon elicitation of tobacco cell cultures with cellulase. Measurable levels of capsidiol and debneyol were found in the tobacco cells and in the culture medium after 8 h of elicitor treatment, with levels continuing to increase for up to 24 h. For the duration of the experiments, the levels of most of the galactolipids and phospholipids were found to decrease in elicited cells and increase in control cells. The most striking change was a rapid decrease in the level of digalactosyldiacylglycerol in elicited cells, to less than 10% of the level in control cells. Among the sterol lipid classes, the most notable changes occurred in the levels of sterol esters and acylated sterol glycosides, which increased significantly in elicited cells within 2 to 4 h after addition of cellulase, but remained unchanged in control cells. Free sterols and sterol glycosides declined slightly, while free fatty acids dropped to low levels 24 h after treatment of cells with cellulase. The present results and those of previous studies indicate that esterification of phytosterols may be a widespread response to environmental or chemical stress.