缓激肽与前列腺素在清醒大鼠中枢作用中有相互关系

近年来神经化学方面的研究证明,前列腺素(PG)可能在中枢神经系统信息传递中具有重要作用。应用组织化学技术也发现,脑内缓激肽(BK)样免疫活性物质的分布。一些作者提出,中枢神经系统中的PG与BK可能存在某种相互作用。近来,Kariga等人为了进一步探讨PG与BK在中枢作用中的可能关系,观察了PGE_2对BK引起的血压变化和行为反应的影响。实验发现,在慢性埋植脑室瘘管的大鼠脑室内注射0.5、1、2、5nmol BK时,动物可产生双峰升压效应,且具有明显的量效关系。与此同时,动物还产生双相的行为改变,表现为短暂兴奋后的持续镇静。反复注射BK,升压反应可快速耐受。如果在使用BK前30分钟,预先在脑室注射PG生物合成抑制剂消炎痛则可抑制BK的升压效应和行为反应。如果在大鼠脑室单纯注射PGE_2也可产生与剂量相关的升压效应以及与BK类似的行为反应。反复脑室注射PGE_2,其升压效应亦可快速耐受,此时如果再在动物脑室     

果实多聚半乳糖醛酸酶分子生物学研究进展

多聚半乳糖醛酸酶（PG酶）是一种在植物细胞壁降解中起重要的作用的酶。作者介绍了PG酶在果实成熟软化中的作用。概述了PG酶基因及其表达调控,评述了乙烯对PG酶合成的影响。     

乙醇对聚半乳糖醛酸酶的活力及荧光光谱,CD光谱的影响

乙醇对PG短时间（不超过36h）的作用可使PG激活,最佳的作用时间是24h,否则乙醇导致PG失活。同时测得乙醇的浓度直接影响PG的活力。在作用时间为24h时,在20％乙醇浓度下,酶的活力最高。乙醇的作用时间及其浓度均影响PG的荧光光谱和CD光谱。这些光谱的变化与酶的活力变化显示了一致性。     

乙醇对聚半乳糖醛酸酶的活力及荧光光谱、CD光谱的影响

乙醇对PG短时间（不超过36h）的作用可使PG激活,最佳的作用时间是24h,否则乙醇导致PG失活。同时测得乙醇的浓度直接影响PG的活力。在作用时间为24h时,在20％乙醇浓度下,酶的活力最高。乙醇的作用时间及其浓度均影响PG的荧光光谱和CD光谱。这些光谱的变化与酶的活力变化显示了一致性。     

前列腺素与消化器官的生理及病理的关系

近10年来,前列腺素(PG)与消化活动的关系已受到人们的重视并得到广泛的研究。本文概要地介绍了PG对消化机能的可能作用,消化器官PG功能异常(如合成过多或过少)与某些消化器官疾病的关系,以及外源性PG和PG合成酶抑制剂在与PG功能改变有关的某些消化器官疾病中的治疗作用。     

白皮杉醇苷在大鼠体内外的葡萄糖醛酸结合代谢研究北大核心CSCD

白皮杉醇苷(PG)是藏边大黄中一种天然抗氧化剂,前期研究发现其极易发生代谢。本文主要研究PG在大鼠体内外的葡萄糖醛酸结合代谢特征。SD大鼠经尾静脉注射给予PG(20 mg/kg),采集给药后胆汁样品,采用LC-MS对主要代谢产物进行结构推测。在此基础上,研究大鼠肝微粒体体外温孵体系中PG的葡萄糖醛酸结合代谢,并测定酶促反应动力学参数。实验结果显示SD大鼠经尾静脉注射给予PG,可在胆汁中快速检测到多种PG及其衍生物的葡萄糖醛酸结合代谢产物。在大鼠肝微粒体体外温孵体系中,PG代谢生成两个与体内一致的单葡萄糖醛酸结合代谢物,其葡萄糖醛酸结合代谢的最大反应速率(Vmax)、米氏常数(Km)和肝内清除率CLint(Vmax/Km)分别为10.11 nmol/(min·mg)、0.36 mmol/L和0.028 m L/(min·mg)。PG经静脉途径进入大鼠体内可经肝脏被快速地广泛代谢,葡萄糖醛酸结合代谢是其体内消除的主要途径之一。大鼠肝脏的葡萄糖醛酸转移酶对PG有较强的亲和力,可催化PG发生快速的葡萄糖醛酸结合代谢。     

PG与番茄果实成熟的关系

系统比较了转多聚半乳糖醛酸酶(PG)反义基因和对照番茄果实成熟过程中绿熟、转色、粉顶、粉红、全红5个时期的PG活性和与其相关的生理、生化组分的动态变化.实验表明,转基因果与对照果相比,PG活性始终处于较低水平,PG活性强烈被抑制是在全红期;果实的硬度、贮藏寿命指数都高于对照果;番茄红素合成积累进程被延缓;可溶性果胶含量、电解质外渗百分率均低于对照果.外源乙烯刺激引起对照果PG活性剧增,而转基因果表现钝化.讨论了PG活性与果实成熟、耐贮性及软化的关系,及对外源乙烯刺激的敏感性.首次明确提出PG活性在对照果中极大地表达,在转基因果中强烈被抑制是在全红期,而不是在整个成熟期;PG活性在果实软化中起直接和重要作用;PG活性的高低与番茄红素的合成与积累有关.     

前列腺素与肾脏功能

前列腺素(PG)几乎存在于体内包括肾脏在内的所有组织。近一二十年来,许多研究者注意并广泛研究肾脏中的PG。本文仅从几个方面介绍PG与肾功能的关系。一、PG对肾血流的作用虽然已知大多数PG能改变肾血流,但对PG在调节肾脏血流中的确切作用仍不十分了解。当给狗和人的静脉或动脉输注PGA_1、PGE_1或PGE_2,或给狗和兔的肾动脉注入PG前体花生四烯酸(arachidonic acid,AA)时,都使肾血流量增加,特别是肾内皮质层的血流量增加更多。PGF_2α仅有轻度的血管扩张作用或没有作用。PGD_2、PGI_2的作用类似     

前列腺素与胃酸分泌的调节

胃粘膜能合成大量前列腺素(PG),PG对胃酸分泌有重要调节作用。外源性PG能强烈抑制胃酸分泌,内源性PG直接或与某些胃肠激素相互作用,对胃酸分泌也具有负反馈调节作用。脑内PG也可能有中枢性抗胃酸分泌的生理作用。PG还具有强烈的胃粘膜保护作用。进一步研究PG与胃酸分泌的关系,对了解PG与消化性溃疡的发病机理有重要作用。     

PG与番茄果实成熟的关系

系统比较了转多聚半乳糖醛酸酶（PG）反义基因和对照番茄果实成熟过程中绿熟、转色、粉顶、粉红、全红5个时期的PG活性和与其相关的生理、生化组分的动态变化。实验表明,转基因果与对照果相比,PG活性始终处于较低水平,PG活性强烈被抑制是在全红期;果实的硬度、贮藏寿命指数都高于对照果;番茄红素合成积累进程被延缓;可溶性果胶含量、电解质外渗百分率均低于对照果。外源乙烯刺激引起对照果PG活性剧增,而转基因果表现钝化。讨论了PG活性与果实成熟、耐贮性及软化的关系,及对外源乙烯刺激的敏感性。首次明确提出PG活性在对照果中极大地表达,在转基因果中强烈被抑制是在全红期 ,而不是在整个成熟期;PG活性在果实软化中起直接和重要作用;PG活性的高低与番茄红素的合成与积累有关。     

Polygalacturonase-inhibiting protein (PGIP) in plant defence: a structural view

Polygalacturonase-inhibiting proteins are plant extracellular leucine-rich repeat proteins that specifically bind and inhibit fungal polygalacturonases. The interaction with PGIP limits the destructive potential of polygalacturonases and might trigger the plant defence responses induced by oligogalacturonides. A high degree of polymorphism is found both in PGs and PGIPs, accounting for the specificity of different plant inhibitors for PGs from different fungi. Here, we review the structural features and our current understanding of the PG-PGIP interaction.     

Polygalacturonase-inhibiting proteins in defense against phytopathogenic fungi

Polygalacturonase-inhibiting proteins (PGIPs) are ubiquitous plant cell wall proteins that are directed against fungal polygalacturonases (PGs), which are important pathogenicity factors. The inhibiting activity of PGIPs directly reduces the aggressive potential of PGs. In addition, it causes PGs to form more long-chain oligogalacturonides that are able to induce defense responses, thereby indirectly contributing to the plant defense. Recent evidence demonstrates that PGIPs are efficient defense proteins and limit fungal invasion. PGIPs and the products of many plant resistance genes share a leucine-rich repeat (LRR) structure, which provides specific recognition of pathogen-derived molecules. The high level of polymorphism of both PGIPs and polygalacturonases is an invaluable tool for deciphering the structure, function and evolution of plant LRR proteins and their ligands. Furthermore, information about PGIP structure and evolution paves the way to the development of efficient strategies for crop protection.     

Pectic enzymes in pectolyase: separation, characterization, and induction of ethylene in fruits

The pectic enzymes in Pectolyase were separated by ion exchange chromatography on Q-Sepharose. Three pectin lyases, two polygalacturonases, and a pectinmethylesterase were resolved. The enzymes were further purified on Mono Q and/or Mono S columns to remove traces of cellulase. The enzymes had molecular weights ranging from 25,000 to 36,000 daltons. They were optimally active between pH 4.0 and 6.2 and were not greatly affected by ions. The pectin lyases and polygalacturonases were endo-enzymes. They solubilized uronic acids from washed cell wall fragments, but the lyases were much more effective than the polygalacturonases. The mixture of enzymes constituting Pectolyase increased ethylene production 15- to 25-fold when introduced into tomato and orange fruits. The enzymes purified from Pectolyase all increased ethylene production in the fruits but the lyases were generally more effective than the hydrolases.     

One-step Concentration and Partial Purification of Aspergillus kawachii Non-acidic Polygalacturonases by Adsorption to Glass Fiber Microfilters

The non-acidic polygalacturonases produced by Aspergillus kawachii in a glucose/tryptone medium were adsorbed to a glass fiber microfilter that was used to clarify the fermentation broth. Maximum adsorption occurred at pH 3 under low ionic strength conditions. The adsorbed activity could be readily released with a buffer solution at pH 5. Based upon these observations, a separation process was developed which enabled the broth to be clarified and, at the same time, the non-acidic polygalacturonases to be concentrated 20-fold and purified 100-fold in a unique filtration step. The practical advantage of recovering polygalacturonases by a filtration process lies in the simplicity and efficiency of the operation involved. Received 27 July 2005; Revisions requested 24 August 2005; Revisions received 16 November 2005; Accepted 16 November 2005     

Comparative biochemical and structural characterizations of fungal polygalacturonases

Endo- and exo-polygalacturonases produced by various fungi are involved in the degradation of pectic substances. They have found a wide range of applications in the food and textile industries. Several phyto-pathogenic fungi secrete polygalacturonases and they act as virulence factors during plant pathogenesis. The comparison of biochemical properties of different fungal polygalacturonases, their mechanism of actions, structural aspects and interactions with inhibitors/proteins could be used as a possible strategy for the fungal-crop disease management. This review focuses on fungal polygalacturonases, including their regulation, comparative biochemical and structural characterizations and their interactions with inhibitors.     

The polygalacturonases of Aspergillus niger are encoded by a family of diverged genes.

Aspergillus niger produces several polygalacturonases that, with other enzymes, are involved in the degradation of pectin. One of the two previously characterized genes coding for the abundant polygalacturonases I and II (PGI and PGII) found in a commercial pectinase preparation was used as a probe to isolate five more genes by screening a genomic DNA library in phage lambda EMBL4 using conditions of moderate stringency. The products of these genes were detected in the culture medium of Aspergillus nidulans transformants on the basis of activity measurements and Western-blot analysis using a polyclonal antibody raised against PGI. These transformants were, with one exception, constructed using phage DNA. A. nidulans transformants secreted high amounts of PGI and PGII in comparison to the previously characterized A. niger transformants and a novel polygalacturonase (PGC) was produced at high levels by A. nidulans transformed with the subcloned pgaC gene. This gene was sequenced and the protein-coding region was found to be interrupted by three introns; the different intron/exon organization of the three sequenced A. niger polygalacturonase genes can be explained by the gain or loss of two single introns. The pgaC gene encodes a putative 383-amino-acid prepro-protein that is cleaved after a pair of basic amino acids and shows approximately 60% amino acid sequence similarity to the other polygalacturonases in the mature protein. The N-terminal amino acid sequences of the A. niger polygalacturonases display characteristic amino acid insertions or deletions that are also observed in polygalacturonases of phytopathogenic fungi. In the upstream regions of the A. niger polygalacturonase genes, a sequence of ten conserved nucleotides comprising a CCAAT sequence was found, which is likely to represent a binding site for a regulatory protein as it shows a high similarity to the yeast CYC1 upstream activation site recognized by the HAP2/3/4 activation complex.     

Purification and characterization of two isozymes of polygalacturonase from Botrytis cinerea. Effect of calcium ions on polygalacturonase activity

The phytopathogenic fungus Botrytis cinerea produces a set of polygalacturonases (PGs) which are involved in the enzymatic degradation of pectin during plant tissue infection. Two polygalacturonases secreted by B. cinerea in seven-day-old liquid culture were purified to apparent homogeneity by chromatography. PG I was an exopolygalacturonase of molecular weight 65 kDa and pI 8.0 and PG II was an endopolygalacturonase of 52 kDa and pI 7.8. Enzymatic activity of PG I and PG II was partially inhibited by 1 mM CaCl2, probably by calcium chelation of polygalacturonic acid, the substrate of the enzyme.     

Various characteristics of growth kinetics and exohydrolase synthesis in Aspergillus foetidus and Zygofabospora marxiana

The kinetics of growth and synthesis of exohydrolases (polygalacturonases and proteinases) were studied in Aspergillus foetidus and Zygofabospora marxiana. The processes of growth and synthesis of polygalacturonases were found to be shifted in time. Endopolymethylgalacturonase of the micromycete and endopolygalacturonase of the yeast are not accumulated in the cells, but are mainly secreted into the growth medium. The maximal value of polygalacturonase bound to the cell coincides with the maximal rate of synthesis of the enzyme secreted into the medium and with the maximal level of cell-bound alkaline and acid proteinases. The activity of alkaline proteinase is not found in the growth medium of the cultures, and only traces of acid proteinase were detected. It is possible that proteinase are involved in processing of endopolygalacturonases.     

Isoelectric characterization of extracellular polygalacturanases of various Aspergillus alliaceus strains

The composition of pectin hydrolase complexes produced by various Aspergillus alliaceus strains was studied under the conditions of induction, catabolite repression, or constitutive synthesis. The strains were found similar in terms of the polygalacturonase spectrum and different with regard to the levels of endo- and exoenzyme activities. The analysis of the zymograms of inducible polygalacturonases revealed that all tested cultures contained at least 24 molecular forms of polygalacturonase. Taking into account only the three molecular forms typical of all analyzed strains of A. alliaceus with pI values of 5.7, 5.9, and 6.3, one can use the spectrum of constitutive, catabolite repression-resistant polygalacturonases as an additional taxonomic species criterion.     

Common amino acid domain among endopolygalacturonases of ascomycete fungi.

The endopolygalacturonase (EC 3.2.1.15) enzymes produced in vitro by three ascomycete fungi, Aspergillus niger, Sclerotinia sclerotiorum, and Colletotrichum lindemuthianum were studied by using thin-layer isoelectric focusing and activity stain overlay techniques. The polygalacturonases from A. niger and S. sclerotiorum consisted of numerous isoforms, whereas the endopolygalacturonase from C. lindemuthianum consisted of a single protein species. The most abundant endopolygalacturonase isoform produced by each of these organisms was purified and characterized. Biochemical parameters, including molecular weight, isoelectric point, kinetic parameters, temperature and pH optima, and thermal stability, were determined. Considerable differences in physical and chemical properties were demonstrated among these fungal polygalacturonases. Antibodies raised against individual proteins exhibited little cross-reaction, suggesting that these enzymes differ structurally as well as biochemically. In contrast, the analysis of the N-terminal amino acid sequences of the three proteins showed extensive homology, particularly in a region labeled domain 1 in which 84% of the amino acids were conserved.