芦丁等天然产物清除活性氧自由基O_(?)~-和·OH的ESR研究

本文用促癌剂PMA(phorbol myristate acetate)刺激人多形核白细胞(PMN)呼吸暴发产生的活性氧自由基,Fenton反应产生的羟自由基·OH,光照核黄素和黄嘌呤/黄嘌呤氧化酶体系中产生的超氧阴离子自由基O(?)为模型,用自旋捕集方法研究天然产物芦丁,槲皮素,异槲皮苷和汉防已甲素对活性氧自由基(?)和·OH的清除作用.除汉防已甲素外,其它药物都能很明显地清除PMN呼吸暴发过程中产生的活性氧自由基.芦丁和异槲皮苷对(?)的清除率分别高达78.1%和79.9%,远远大于维生素E(12.7%)的作用.除汉防已甲素外,其它三种药物对·OH的清除作用也大于维生素E.四种天然产物对O(?)和·OH的清除作用都小于维生素C.     

含硒银杏叶清除羟基自由基的ESR研究

利用电子自旋共振技术(ESR)研究了含硒银杏叶提取物对H_2O_2-Fe~(2 )体系产生的羟基自由基的清除作用.与SOD、茶多酚相比,含硒银杏叶提取物对羟基自基也有很强的清除效果.增添了有实用价值的天然、无公害的清除羟基自由基的新资源.     

茶儿茶素氧化产物体外清除·OH自由基作用的研究

本文采用２－脱氧－Ｄ－核糖（ＤＲ）法产生．ＯＨ,测定了不同浓度的茶儿素氧化产物Ａ及Ｃ对．ＯＨ的清除作用。结果表明,在一定的浓度范围内,氧化产物Ａ及Ｃ均有很强的清除．ＯＨ的作用且最佳清除浓度为２００μｇ／ｍｌ。在茶多酚、氧化产物Ａ及Ｃ三种物质中,以产物Ｃ的清除作用最强,其ＩＣ５０值为７．３μｇ／ｍｌ,其次是Ａ,ＩＣ５０为１０．１μｇ／ｍｌ,最后是茶多酚,ＩＣ５０值为７０μｇ／ｍｌ。     

巨噬细胞产生NO.和O_2~-自由基的分子机理

建立了用顺磁共振（ＥＳＲ）和化学发光技术测定巨噬细胞产生ＮＯ和氧自由基的方法．捕捉到了巨噬细胞受佛波酯刺激产生的ＮＯ．和Ｏ－２自由基．测定了在不同浓度Ｌ－精氨酸存在时佛波酯刺激后巨噬细胞产生的ＮＯ自由基．研究了巨噬细胞产生的ＮＯ和氧自由基的分子机理．结果表明巨噬细胞不仅产生氧自由基而且产生ＮＯ自由基．ＮＡＤＰＨ氧化酶产生氧自由基的部位位于巨噬细胞膜的外侧．ＮＯ合成酶活化产生ＮＯ自由基比ＮＡＤＰＨ氧化酶活化产生氧自由基晚几分钟．     

含硒银杏叶清除羟基自由在的ESR研究

利用电子自旋共振技术（ＥＳＲ）研究了含硒银杏叶提取物对Ｈ２Ｏ２－Ｆｅ＾２＋体系产生的羟基自由基的清除作用。与ＳＯＤ、茶多酚相比,含硒银杏叶提取物对羟基自基也有很强的清除效果,增添了有实用价值的天然、无公害的清除羟基自由基的新资源。     

芦丁-锗配合物及其自由基清除活性研究

芦丁是存在于多种植物中的天然多羟基黄酮苷,能与多种金属离子形成配合物。本文采用紫外分光度法考察了芦丁与锗离子的配位作用,并研究了芦丁-锗配合物清除超氧自由基和DPPH自由基的作用。结果显示在KH2PO4-NaOH(pH6．70)的缓冲液中,芦丁与锗离子能形成1：1的配合物,其K稳=10^7.46,同时配合物显示有较好的自由基清除活性。     

金属硫蛋白与·OH和O_2~-反应的动力学

以DMPO(5.5-dimethyl-1-pyrroline-N-oxide)为自旋捕捉剂,通过ESR技术测定了兔肝金属硫蛋白(ZnMT_1、ZnMT_2、CdMT_1和CdmT_2)与·OH反应的速率常数.并利用金属硫蛋白与高铁细胞色素C(ferricytochrome C)竞争O_2~-的反应,测定了这四种MT与O_2~-的反应速率常数.结果表明,k_(OHMT)与MT亚型及结合金属有关,对上述四种MT其顺序为ZnMT_2>ZnMT_1>CdMT_2>CdMT_1.而四种MT的k_(O_2~-MT)无明显差异.     

高等植物光系统Ⅱ中强光照射产生超氧阴离子自由基的ESR探索

利用自旋捕捉电子顺磁共振（ESR）的方法对从菠菜叶绿体中分离提纯的光系统Ⅱ(PSⅡ)颗粒产生O₂^-_·的机理进行了直接检测.通过对样品充氧、加入超氧化物歧化酶（SOD）抑制剂四氰乙烯（TCNE）以及原位光照检测ESR信号等手段，在PSⅡ中检测到O₂^-_·与DMPO加合物的特征ESR信号.而在没有SOD抑制剂的情况下，光照时PSⅡ中O₂^-_·与DMPO加合物浓度显著下降.进一步实验发现PSⅡ中O₂^-_·产率与氧分子浓度直接正相关.O₂^-_·产率还具有pH值依赖性，在pH值为6.0～6.5范围内，O₂^-_·产率最高，大于此范围时则呈显著下降趋势.而PSⅡ颗粒的Tris处理也将导致O₂^-_·产率的急剧减少.以上结果证实水裂解放氧十分活跃的PSⅡ也是高等植物叶绿体在光照下产生活性O₂^-_·的主要部位，通常大部分的O₂^-_·能被内源SOD清除，且O₂^-_·的生成与PSⅡ的电子传递活性密切相关.     

用ESR技术研究含硒蛋白抗羟基自由基作用的活性

用ＥＳＲ技术研究含硒蛋白抗羟基自由基作用的活性。与ＳＯＤ、茶多酚相比较,含硒蛋白对羟基自由基的清除也有显著作用。找到了一种有实用价值,天然无毒,抗羟基自由基的新资源。     

ESR and U-series analyses of enamel and dentine fragments of the Banyoles mandible

The Banyoles mandible presents a puzzle. Its anatomy has been described as pre-Neandertal, but the travertine in which it was found has been dated to 45,000 +/- 4000 years. By this time, any pre-Neandertals had supposedly been absent from the European fossil record for more than 100,000 years. It was therefore proposed that the age of the travertine may represent a minimum age estimate, with the mandible possibly having been reworked from older deposits. We carried out a non-destructive ESR analysis of an enamel fragment removed from a molar and performed a series of in situ laser ablation U-series analyses on dentine fragments adjacent to the enamel piece. The analyses resulted in an apparent combined ESR-U-series age of 66,000 +/- 7000 years. The encasing travertine matrix was also analyzed for U-series isotopes and showed signs of U-mobilization. It cannot be excluded that the travertine matrix is older than the previously determined age. If the mandible was not reworked, then the combined ESR-U-series result on the tooth enamel would give its best age estimate. If, on the other hand, the mandible was reworked from another deposit, the actual ESR-U-series age will depend on the external dose rate from the previous matrix and the depth of its burial, which controls the degree of the attenuation of the cosmic dose rate over time. Considering a range of possible burial histories, the mean age of the mandible would lie somewhere between the combined ESR-U-series age and the previously determined age of the travertine matrix. Regarding the morphology of the mandible, a review of its features in the context of larger Neandertal samples indicates that the anatomy of the specimen is not incompatible with such a young age determination, although it further highlights morphological variation in the late Neandertal sample.     

ESR spin label studies of the nucleosome core particle and histone core

An imidazole spin label has been used to study the accessibility and conformational state of tyrosines in both the nucleosome core particles and histone core extracted from chicken erythrocytes. About 40% of the tyrosyl residues in the histone core can be labeled under nondenaturing conditions. However, less than 15% of the tryosyls in the nucleosome core particle can be labeled even at 200- to 300-fold M excess of label. The effect of urea on the conformational state of the spin-labeled tyrosyls in both the nuclesome core particles and the histone core has been studied. Ionic effects on the spin-labeled nucleosome core have been investigated. Several conformational transitions are observed in the range of 1 mM NaCl to 2.5 M NaCl. Three major transitions are found at 0.1 M to 0.6 M, 0.7 M to 1.8 M and 2 M to 2.5 M NaCl, respectively. The observed changes can be interpreted as swelling and conformational change of the inner histone core, gradual separation of DNA from the histone core, and tightening of the histone core.