金属离子螯合剂对橙汁中L—抗坏血酸的保护及其机理探讨

本文研究了在加热过程中金属离子螯合剂植酸、聚磷酸钠和EDTANa_2对橙汁和橙汁模拟体系中L—抗坏血酸的稳定作用,并采用红外光谱和紫外差光谱对EDTANa_2的保护机理作了初步探讨。结果表明:植酸和聚磷酸钠均不能降低Cu~(2+)对橙汁模拟体系中L—抗坏血酸氧化降解的催化作用,而EDTANa_2不仅能络合Cu~(2+),减少L—抗坏血酸的催化降解损失,而且红外光谱和紫外差光谱及溶剂微扰研究还揭示出EDTANa_2可与L—抗坏血酸形成氢键保护,这种氢键保护作用受到糖和柠檬酸的不利影响。     

非水介质中辣根过氧化物酶（HRP）荧光活性测定法

建立了一种分析ＨＲＰ催化活力的新方法。该方法基于单体（底物）、聚合物（产物）的荧光发射光谱不重叠,使用荧光光谱仪,通过测量底物荧光淬灭来检测ＨＲＰ在非水介质中（二氧六环－水、乙醇－水、丙酮－水体系）催化酚类、芳香胺类物质聚合的活力。此方法迅速、简便,结果是定量并可重复的,并能定量地计算底物转化率。     

Evidence that methylation of the FMR-I locus is responsible for variable phenotypic expression of the fragile X syndrome.

DNA at the FMR-1 locus was analyzed by Southern blot using probe StB12.3 in an unusual fragile X family with six brothers, three of whom are affected with fragile X to varying degrees, two of whom are nonpenetrant carriers, and one of whom is unaffected. Fragile X chromosome studies, detailed physical examinations, and psychological testing were completed on all six. Two of the affected brothers and the two nonpenetrant brothers were found to be methylation mosaics. The three affected males spanned the phenotypic and cognitive spectrum of the fragile X syndrome. A correlation was seen between the degree of methylation and the phenotypic expression identified in the three affected males. The two males initially classified as nonpenetrant were found to have mild phenotypic expression which consisted of minor cognitive deficits and a partial physical phenotype. These two, who were negative on fragile X chromosome studies, were found on DNA analysis to have large broad smears, with approximately 97% of the DNA unmethylated. The results described here indicate that some "nonpenetrant" carrier males may have varying amounts of methylation of the FMR-1 region, which can result in mild expression of the fragile X syndrome. The apparently mild phenotypic and cognitive expression of the fragile X syndrome in the two males, initially classified as nonpenetrant, who are mosaic for hypermethylation of an expansion of the CGG repeat in the premutation range, indicates that expression of the syndrome is not confined to males with large, hypermethylated expansions (full mutation) but has instead a gradient effect with a threshold for the full expression of the phenotype.     

盐酸胍诱导的α淀粉酶去折叠与再折叠

利用蛋白质内源荧光和酶活性两种信号以及荧光偏振,HPLC和停流等方法研究了盐酸胍诱导的α淀粉酶去折叠与重折叠的平衡转变和动力学。实验结果表明α淀粉酶去折叠与重折叠是两个不同的过程;变性与复性过程中可能伴有聚集体生成;去折叠与重折叠均为双相过程,重折叠大约始于2秒之后。     

黄花棘豆的喹诺里西定生物碱

豆科棘豆属有毒植物含多种有毒生物碱,有关棘豆属中生物碱成分的研究,早在1929年Couch由兰伯氏棘豆(Oxytropis lambertii DC.)中分离到一种多羟基化的含氮有机化合物,这是最早报道由棘豆属植物中分离出的生物碱成分,由于当时条件限制未能确定其结构。1982年美国农业部西部研究中心的植物化学家Molyneux从绢毛棘豆(Oxytropis sericea)中分离到苦马豆碱(swainsonine)等吲哚里西定生物碱(indolizidinealkaloids);1989年沈阳药学院于荣敏等由小花棘豆(Oxytropis glabra DC.)中分离出多种喹诺里西定生物碱。喹诺里西定生物碱具有多种生理活性,对试验动物中枢神经系统产生抑制,呼吸抑制或兴奋,致幻、流产和致畸等作用。本文报道由黄花棘豆(Oxytropis ochrocephala Bunge)中测得4种喹诺里西定生物碱。     

鼎湖山自然林豆科固氮植物资源的调查研究

本文在调查鼎湖山自然林木本豆科植物结瘤固氮的基础上,参阅了国内外有关豆科植物结瘤固氮的主要文献,研究了鼎湖山自然林木本豆科植物的固氮资源。结果得出鼎湖山自然林中常见的木本豆科植物共有41种,其中乔木15种,灌木6种,木质藤本20种;有结瘤固氮特性的26种,其中乔木11种,灌木5种,木质藤本10种;经初步调查未见根瘤的6种,其中乔木2种,灌木1种,木质藤本3种;未调查的9种,其中乔木2种,木质藤本7种。本研究结果为鼎湖山木本豆科固氮植物资源的保护、管理和开发利用提供了科学论据,在理论和应用方面均有重要意义。     

Modulation of mechanosensitive calcium-selective cation channels by temperature

Gating of associations of mechanosensitive Ca²⁺-selective cation co-channels in the plasmalemma of onion epidermis has a strong and unusual temperature dependence. Tension-dependent activity rises steeply as temperature is lowered from 25°C to about 6°C, but drops to a low level at about 5°C. Under the conditions tested (with Mg²⁺ and K⁺ at the cytosolic face of outside-out membrane patches), promotion results both from more bursting at all observed linkage levels and from longer duration of bursts of co-channels linked as quadruplets and quintuplets. Co-channel conductance decreases linearly, but only modestly, with declining temperature. It is proposed that these and related mechanosensitive channels may participate in a variety of responses to temperature, including thermonasty, thermotropism, hydrotropism, and both cold damage and cold acclimation.     

Correlation between arrested secondary plasmodesmal development and onset of accelerated leaf senescence in yeast acid invertase transgenic tobacco plants

Mature leaves of a transgenic tobacco plant ( Nicotiana tabacum L var. Samsun, line A41-10) that constitutively express a yeast-derived acid invertase gene develop symptoms which are characterized by the presence of greenish-yellow and green sectors in the same leaf, and onset of early, leaf senescence. Previous studies indicated that invertase activity was two- to threefold higher in the greenish-yellow sectors than in the green sectors. Our structural analyses revealed that development of secondary plasmodesmata, via modification of existing primary plasmodesmata, between mesophyll cells was inhibited severely in the greenish-yellow sectors, but only marginally in the green sectors. In contrast, the structure and function of primary plasmodesmata in the same symptomatic sectors remained unaltered as determined by structural and dye coupling studies. It is hypothesized that secondary plasmodesmata differ from primary plasmodesmata in having special abilities to traffic information molecules to coordinate leaf development and physiological function(s). Arrest of secondary plasmodesmal development by high invertase activity in the transgenic tobacco leaf may have prevented this type of trafficking and hence resulted in early leaf senescence. The results also indicate that the yeast acid invertase-expressing tobacco may provide an effective experimental system for the molecular characterization of cellular mechanisms that regulate the development, function, and possible turnover of secondary plasmodesmata.