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.     

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     

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...     

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。     

Raman spectroscopic study of DNA after photosensitive damage caused by hypocrellins A and B

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Preliminary dielectric measurement and analysis protocol for determining the melting temperature and binding energy of short sequences of DNA in solution

Measurement of the real dielectric constant of bulk buffer solutions containing short sequences of DNA as a function of temperature through the DNA melting or denaturiztion transition can be used to determine melting temperatures, T(m), and to estimate the binding energy of the complimentary strands. We describe a preliminary dielectric measurement and analysis protocol to determine these parameters and its application to two known short sequences. The relative real dielectric constant for the bulk solutions was determined over the frequency range of 50 Hz-20 kHz and temperature range of <40-65 degrees C. The measurements were performed on dilute solutions and utilized low electric field strengths. Based on fits to the data by modified sigmoid functions, the melting temperatures, width of transition, and binding energy for the two sequences in solution were estimated. It was observed that the order of the transition appeared to be second order. The results were then compared against predictions of a number of models from the literature that provide theoretical estimates for the melting temperatures of known short sequences of DNA.     

Redox and Chemical Activities of the Hemes in the Sulfur Oxidation Pathway Enzyme SoxAX

SoxAX enzymes couple disulfide bond formation to the reduction of cytochrome c in the first step of the phylogenetically widespread Sox microbial sulfur oxidation pathway. Rhodovulum sulfidophilum SoxAX contains three hemes. An electrochemical cell compatible with magnetic circular dichroism at near infrared wavelengths has been developed to resolve redox and chemical properties of the SoxAX hemes. In combination with potentiometric titrations monitored by electronic absorbance and EPR, this method defines midpoint potentials (E_m) at pH 7.0 of approximately +210, −340, and −400 mV for the His/Met, His/Cys⁻, and active site His/CysS⁻-ligated heme, respectively. Exposing SoxAX to S₂O₄²⁻, a substrate analog with E_m ∼−450 mV, but not Eu(II) complexed with diethylene triamine pentaacetic acid (E_m ∼−1140 mV), allows cyanide to displace the cysteine persulfide (CysS⁻) ligand to the active site heme. This provides the first evidence for the dissociation of CysS⁻ that has been proposed as a key event in SoxAX catalysis.     

Comparison of antioxidant abilities of magnolol and honokiol to scavenge radicals and to protect DNA

The antioxidant properties of magnolol and honokiol were evaluated in the experimental systems of reducing ONOO⁻ and ¹O₂, bleaching β-carotene in linoleic acid (LH) emulsion, and trapping 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonate) cationic radical (ABTS⁺) and 2,2′-diphenyl-1-picrylhydrazyl radical (DPPH), and then were applied to inhibit the oxidation of DNA induced by Cu²⁺/glutathione (GSH) and 2,2′-azobis(2-amidinopropane hydrochloride) (AAPH). Magnolol and honokiol were active to reduce ONOO⁻ and ¹O₂. Honokiol showed a little higher activity to protect LH and to inhibit Cu²⁺/GSH-induced oxidation of DNA than magnolol. In addition, honokiol exhibited higher activities to trap ABTS⁺ and DPPH than magnolol. In particular, honokiol trapped 2.5 radicals while magnolol only trapped 1.8 radicals in protecting DNA against AAPH-induced oxidation. The obtained results suggested that low antioxidant ability of magnolol may be related to the intramolecular hydrogen bond formed between di-ortho-hydroxyl groups, which hindered the hydrogen atom in hydroxyl group to be abstracted by radicals. Therefore, the antioxidant capacity of magnolol was lower than that of honokiol.     

The Effects of Different Buffers on the Oxidation of DNA by Thiols and Ferric Iron

Because buffers can act as metal ligands, they can effect several reactions necessary for DNA oxidation by ferric iron and thiols, such as iron reduction. Therefore, these reactions were studied in Hepes and phosphate buffers and unbuffered NaCl. Reduction of Fe³⁺ by dithiothreitol (DTT) and cysteine was observed in either Hepes or NaCl solutions, but not in phosphate buffer. Thiyl radicals were observed in Hepes, but there was much less thiyl radical production in the saline or phosphate solutions. Redox cycling between either DTT or cysteine and Fe³⁺ also resulted in dioxygen consumption in Hepes buffer. Reduction of Fe³⁺ and O₂ resulted in the formation of an oxidant capable of producing 8-hydroxy-2′-deoxyguanosine (8-OHdG) in calf-thymus DNA. The highest levels of 8-OHdG were detected when DTT or cysteine and Fe³⁺ were incubated in Hepes, while much less DNA oxidation was detected when the experiment was done in a saline solution, and almost no DNA oxidation occurred in the phosphate buffer. These results demonstrate that the use of different buffers can greatly affect the ability of thiols to promote iron-dependent oxidations. © 1997 John Wiley & Sons, Inc. J Biochem Toxicol 12: 125–132, 1998     

Involvement of histidine in complex formation of PriB and single-stranded DNA

PriB is a basic 10-kDa protein that acts as a facilitator in PriA-dependent replication restart in Escherichia coli. PriB has an OB-fold dimer structure and exhibits single-stranded DNA (ssDNA)-binding activities similar to single-stranded binding protein (SSB). In this study, we examined PriB's interaction with ssDNA (oligo-dT35, -dT15, and -dT7) using heteronuclear NMR analysis. Interestingly, ¹H or ¹⁵N chemical shift changes of the PriB main-chain showed two distinct modes using oligo-dT35. The chemical shift perturbation sites in the primary mode were consistent with the main contact site in PriB–ssDNA, which was previously determined by crystal structure analysis. The results also suggested that approximately 8 nt in ssDNA was the main contact site to PriB. In the secondary mode, residues in the α-helix region (His57–Ser65) and in β4–loop3–β5 were mainly perturbed. On the other hand, we examined the state of ssDNA by FRET using 5′-Cy3- and 3′-Cy5-modified oligo-dT35. As the PriB concentration increased, two-step saturation curves were observed in the FRET assay, suggesting a compact structure of ssDNA. Moreover, we confirmed two-step PriB binding to oligo-dT35 using EMSA. The pH dependence of FRET suggested contribution of the His residues. Therefore, we prepared His mutants of PriB and found that His64 in the α-helix region contributed to the second interaction between PriB and ssDNA using FRET and EMSA. Thus, from a structural standpoint, we suggested the role of His64 on the compactness of the PriB–ssDNA complex and on the positive cooperativity of PriB.     

The effect of scatter correction and radius of rotation on semiquantitative measurements in SPECT 123I-FP-CIT imaging. A phantom study

PurposeThe high energy emissions of ¹²³I and the suboptimal radius of rotation affect the semiquantitative measurements performed during ¹²³I-FP-CIT tomographic imaging. An in-house extra low cost striatum phantom with brain and striatum compartments was constructed and was used to study the effects of Triple Energy Window scatter correction (TEW-SC) and radius of rotation on the Specific Binding Ratio (SBR) measurements.Materials and methodsThe phantom compartments were filled with radioactive ¹²³I solutions with varying concentrations, in a series of experiments. Tomographic images were acquired at six different radii of rotation, with and without TEW-SC and the SBRs were calculated using appropriate regions of interest, as in clinical imaging.ResultsSBRs decreased with increasing radius of rotation in both non-SC and TEW-SC images, the decrease being more pronounced in the latter. The application of TEW-SC increases SBR values by 40% on average. A maximum %Recovery of 42.7% of the true SBR value was achieved in the non-SC images, which increased to 64.6% after TEW-SC. Appropriate correction factors (CF) were calculated in order to make the SBR values independent on the radius of rotation, which could be used to correct SBR values obtained from tomographic acquisitions with suboptimal radius of rotation.ConclusionThe use of appropriate CF can provide more consistent SBR values and a more meaningful comparison between SBRs calculated from images acquired at different radii of rotation.