竹红菌甲素敏化质粒pBR 322 DNA光氧化——使封闭环DNA转变为开环DNA

甲素可敏化质粒pBR 322 DNA光氧化断链的使其封闭环DNA转变为开环DNA。甲素敏化pBR 322 DNA光氧化反应可被单线态氧淬灭剂-NaN_3抑制,证明此光敏氧化机制属Ⅱ型过程。     

竹红菌甲素与半胱氨酸作用的ESR研究

本文用ESR方法研究了竹红菌甲素和半胱氨酸在光和暗条件下产生活性氧的过程.我们发现甲素具有氧化还原反应中间载体的作用,即巯基化合物将电子转移给甲素,而甲素在有氧的条件下再将电子转移给氧生成超氧阴离子自由基.光照可以加快这一步骤,使用化学方法定量研究证明激发态甲素与半胱氨酸的反应速率大于基态甲素.除半胱氨酸外,巯基乙醇和还原谷胱甘肽均可以将电子经甲素传给氧,而甲硫氨酸和胱氨酸不具这一能力,这说明巯基在反应中很重要而硫原子不是必需的.     

竹红菌甲素在脂质体中的光谱性质和结合能力研究

竹红菌甲素在脂质体中的光谱性质和结合能力研究邹伟,安静仪,蒋丽金（中国科学院北京感光化学研究所,１００１０１）关键词竹红菌甲素;光谱特性;结合;脂质体竹红菌甲素（Ｒ人）是一种新型并配类光疗药物,临床上治疗一些皮肤病效果显著”’,研究表明ＨＡ对癌细胞有...     

赤霉素及竹红菌甲素荧光量子产率的常量化区域

通过对赤毒素、竹红菌甲素及苯酚量子产率的测定与比较发现,这三种荧光化合物都具有一个相对于激发波长的量子产率的稳定区域。尽管它们具有多个激发峰,但不同激发峰所激发的荧光量子产率差别较小。竹红菌甲素在室温放置一个月,690nm荧光光谱有明显的改变。以上结果提示在测定未知荧光化合物的量子产率时,被测溶液的散射较强,同时荧光物的激发与发射波长彼此相接近。量子产率较弱时,可以在最大激发峰的蓝移方向上选择激发波长来避免散射光的干扰,提高量子产率测定的准确度。竹红菌甲素在690nm的荧光肩峰,可能是分子空间结构上容易发     

某些物理化学因素对竹红菌甲素敏化的人红细胞膜乙酰胆碱酯酶的光失活作用的影响

本文以人红细胞膜乙酰胆碱酯酶力作用对象,研究了甲素浓度、pH、温度等因素对甲素致敏的酶光失活的影响,并计算了不同条件下的酶失活速率常数.甲素与某些光敏化剂相比,有以下特点:(1)甲素光敏化效率随着pH降低而增加,(2)光强指数α>1,(3)甲素在400nm—600nm波长范围内均有较大的光敏化作用.后性氧清除剂的试验结果表明,乙酰胆碱酯酶的光失活主要是单线态氧的作用,其它活性氧也有一定作用.     

竹红菌甲素敏化嘌呤和嘧啶碱的光氧化作用及其影响因素

本工作利用光吸收和高效液相色谱(HPLC)技术研究了甲素对DNA分子中四种碱基A、G、C和T光氧化的敏化作用,发现在反应体系的pH为9.0、甲素浓度为3×10~(-5)mol/L、光照40分钟时,G和T紫外吸收明显降低;HPLC分析发现甲素敏化的G光氧化体系比对照体系多出现一组分峰(滞留时间0.927分钟),该峰用475nm波长检测比260nm波长检测灵敏。根据反应机制推测是G环破裂产物。在反应条件固定时,甲素敏化G的光氧化作用受pH、光照时间及甲素浓度影响极大。单线态氧淬灭剂——叠氮钠浓度在40—110mmol/L可部分抑制甲素敏化G的光氧化作用,>110mmol/L时反应完全被阻断,提示甲素对G光氧化的敏化作用主要通过单线态氧(~1O_2)即Ⅱ型机制起作用。本文还讨论了G光氧化的可能途径。     

竹红菌甲素-脂质体的制备及其特性

利用反相蒸发技术制备了竹红茵甲素脂质体体系,测定了其光谱和稳定性,结果表明:在该体系中,竹红菌甲素的Ⅰ吸收峰、荧光峰均出现红移且有荧光增强效应。竹红菌甲素-脂质体(浓度0.05～0.5mg/ml)在4℃下存放2-3d,光密度下降5％左右。     

卟啉化合物四-[3-甲氧基-4-(N-咔唑)]正丁氧苯基和四-[3-甲氧基-4-(N-咔唑)]正己氧苯基与小牛胸腺DNA相互作用的研究

〔四-[3-甲氧基-4-(N-咔唑)正丁氧苯基],4C4-TPP〕和〔四-[3-甲氧基-4-(N-咔唑)正己氧苯基],4C6-TPP〕是两个结构相似但侧链不同的卟啉化合物,4C6-TPP的侧链长于4C4-TPP。应用紫外吸收光谱、荧光光谱和园二色谱,研究了4C4-TPP和4C6-TPP与小牛胸腺DNA（Calf thymus, ctDNA）之间的相互作用。结果表明：4C4-TPP和4C6-TPP均以侧链插入DNA与之作用,计算二者与DNA之间的结合常数,4C6-TPP与DNA的结合常数远大于4C4-TPP与DNA的结合常数。基于4C4-TPP与4C6-TPP二者之间结构差异仅在于侧链基团,证明了侧链基团对于卟啉与DNA作用的影响不是主要决定于其空间尺寸大小,取代基化学结构是影响卟啉与DNA的相互作用的重要因素。     

RELATIVE STABILITY OF QUADRUPLEXES CONTAINING DIFFERENT NUMBER OF G-TETRADS

The aim of this work is to compare the physicochemical properties of three oligonucleotidic sequences, d(TGGGT), d(TGGGGT) and d(TGGGGGT), which assemble to form quadruplex structures with the same molecularity, but containing three, four, and five G-quartets, respectively. The addition of one or two G-tetrads greatly increases both the enthalpy and T_m values of the quadruplex dissociation.     

Pigment Interactions in Light-harvesting Complex II in Different Molecular Environments

Extraction of plant light-harvesting complex II (LHCII) from the native thylakoid membrane or from aggregates by the use of surfactants brings about significant changes in the excitonic circular dichroism (CD) spectrum and fluorescence quantum yield. To elucidate the cause of these changes, e.g. trimer-trimer contacts or surfactant-induced structural perturbations, we compared the CD spectra and fluorescence kinetics of LHCII aggregates, artificial and native LHCII-lipid membranes, and LHCII solubilized in different detergents or trapped in polymer gel. By this means we were able to identify CD spectral changes specific to LHCII-LHCII interactions, at (−)-437 and (+)-484 nm, and changes specific to the interaction with the detergent n-dodecyl-β-maltoside (β-DM) or membrane lipids, at (+)-447 and (−)-494 nm. The latter change is attributed to the conformational change of the LHCII-bound carotenoid neoxanthin, by analyzing the CD spectra of neoxanthin-deficient plant thylakoid membranes. The neoxanthin-specific band at (−)-494 nm was not pronounced in LHCII in detergent-free gels or solubilized in the α isomer of DM but was present when LHCII was reconstituted in membranes composed of phosphatidylcholine or plant thylakoid lipids, indicating that the conformation of neoxanthin is sensitive to the molecular environment. Neither the aggregation-specific CD bands, nor the surfactant-specific bands were positively associated with the onset of fluorescence quenching, which could be triggered without invoking such spectral changes. Significant quenching was not active in reconstituted LHCII proteoliposomes, whereas a high degree of energetic connectivity, depending on the lipid:protein ratio, in these membranes allows for efficient light harvesting.     

Preferred interaction of d-peptidyl-anthraquinones with double-stranded B-DNA

The quest for more specific drugs in antitumor chemotherapy led us to the design of anthraquinone–peptide conjugates capable of selective recognition of the nucleic acid. We present here the DNA binding characteristics, sequence specificity and geometry of interaction of a pair of enantiomers containing the lysine–glycine dipeptide in the side chains. The d enantiomer binds right handed double stranded DNA more efficiently than the l form under all conditions tested. The source of higher binding affinity is not electrostatic in nature and rests in the more favorable hydrophobic contacts of the d-lysyl side chains in the drug-DNA complex. Both derivatives exhibit preference for alternating GC base sequences and intercalate into DNA in a threading mode as suggested by chiroptical and theoretical studies. The d enantiomer, being a peptidyl derivative that contains a non-natural amino acid, has the considerable advantage of being less susceptible to enzymatic hydrolysis and could therefore represent a lead compound for further development.     

岩豆凝集素的圆二色性与生物学活性关系的研究

岩豆凝集素（ＭＤＬ）的远紫外圆二色性谱（ＣＤ谱）显示２１６－２１７ｎｍ处的单一负峰。此时ＭＤＬ分子含有１６．２％的α螺旋,４６．３％的β折叠和３７．５％的无规卷曲。ｐＨ９．０时负峰红移至２２０ｎｍ,且在２１７－２２２ｎｍ处的峰值几乎相同;在２０－４０℃范围内,ＣＤ谱的变化甚微;６０℃时谱峰蓝移;在８０℃或１００℃时,２１２ｎｍ处出现一大负峰。１ｍｏｌ／Ｌ或２ｍｏｌ／Ｌ脲时,ＭＤＬ的ＣＤ谱已发生明显变化,二级结构单元也有变化,凝集兔红细胞的活性也随之减弱;随脲浓度的增加,ＭＤＬ的谱峰蓝移,最终在２１２ｎｍ处出现大负峰。当胍浓度为０．７５ｍｏｌ／Ｌ时,ＭＤＬ的ＣＤ谱即有明显变化和活性丧失;胍浓度继续增加,ＣＤ谱逐渐成为特征的无规卷曲的谱形。在ｐＨ９．０、温度超过８０℃、脲或胍浓度分别高于２ｍｏｌ／Ｌ和０．７５ｍｏｌ／Ｌ时,ＭＤＬ的ＣＤ谱发生显著变化的同时,其凝集兔红细胞的生物学活性全部丧失,分子的二级结构单元也发生很大改变。