甜叶悬钩子叶的甜味成分研究

甜叶悬钩子(Rubus suavissimus S.Lee)又称甜茶,是蔷薇科(Rosaceae)中一种含甜味物质的灌木。该种植物曾被鉴定为悬钩子(Rubus palatis Thunb.)或秦氏悬钩子(Rubus chingii Hu),但其地理分布范围较狭窄,外部形态特征及其内含化合物与上述两种亦有所不同。     

甜叶悬钩子(Rubus suavissimus S.Lee)中UDP-糖基转移酶基因的克隆、表达及序列分析

糖基化是植物次生代谢产物生物合成中重要的修饰反应。目前已报道的以二萜为底物的UDP-糖基转移酶(UGT)数量稀少。本研究基于甜叶悬钩子叶片的转录组数据,利用生物信息学分析手段,选定可能具有二萜类催化活性的UDP-糖基转移酶基因进行克隆。最终克隆得到18条UGT基因序列,在大肠杆菌中进行了异源表达,并对克隆的基因进行了初步的序列分析。本研究为进一步挖掘和验证甜叶悬钩子中UGT的功能奠定了基础。     

应乐果甜蛋白及其基因工程

应乐果甜蛋白（monellin)是一种分子量为10.7kD的超甜蛋白。由A,B两条链组成,其中A链44个氨基酸,B链50个氨基酸。分子内有5个反向平行的β折叠链和一个α螺旋。实验表明,Asp^B7可能是应乐果甜蛋白的甜味活性中心。此外,Cys^41,Ca^2 等对应乐果甜蛋白的甜味也会产生影响。研究人员把应乐果甜蛋白的单链类似物相断转入大肠杆菌,土豆,莴苣和酵母中,得到了具甜味,稳定性和耐受力强的表达产物。     

甜茶的成分研究

<正> 甜茶 Rubus suavissimus S.Lee 叶的化学成分研究表明,有甜茶素、多酚类、蛋白质、氨基酸、维生素C以及矿物质等,简报如下: 一、甜茶叶的甜味成分主要为比蔗糖甜300倍的甜茶素,干甜茶叶的甜茶素含量在1.5％左右,经我们鉴定,其化学结构和Stevioside(斯替维甙)相同,是一种低热值的非糖的甜味物质,可供代糖食用。     

奇甜蛋白基因在园艺作物中的表达

奇甜蛋白（thaumatin）是从非洲西部植物katemfe（Thaumatococcus daniellii Benth）中提取得到的几种关系相近的甜味蛋白的统称,其中最主要的为奇甜蛋白Ⅰ和奇甜蛋白Ⅱ。奇甜蛋白不仅甜度高,而且具有低热量、安全无毒以及不易诱发糖尿病等优点。因此,将奇甜蛋白基因转入园艺作物中并使之表达,用以提高可食部分的甜味,有其特别的研究意义。奇甜蛋白基因已先后在马铃薯、梨树、黄瓜、番茄等园艺作物得到表达,但仍有一些问题需要解决。现从奇甜蛋白基因的克隆、测序与表达,转基因果实的安全性检测,甜度的感官评价,甜味遗传特点以及奇甜蛋白抗真菌病害检验等几个方面综述了国内外研究进展,并对今后的研究提出了建议。     

植物甜蛋白Thaumatin研究进展

甜蛋白自 2 0世纪 70年代发现以来 ,一直倍受人们关注 ,而源于自然的Thaumatin是植物甜蛋白中的一种 ,它具有低热量、高甜度、安全无毒 ,并可降解为人体所需的氨基酸等多种优点 ,是一种新型甜味剂。在物质文化生活日益丰富的今天 ,人们越来越重视饮食的科学性 ,吃饱的同时更加关注所摄入食品的品质 ,无疑具多功能的非糖类物质 Thaumatin就是人们所需求的理想食品。因此 ,Thaumatin成为热门研究领域之一也就不足为怪了。1 　植物甜蛋白研究概况迄今为止 ,人们从多种植物中发现并分离出 7种甜味蛋白 [1 ]。更确切地说 ,其中 5种( Thaumatin,…     

植物甜蛋白的研究进展

本文简要介绍了近年来在植物中发现的几种甜味蛋白质的分子结构及其化学性质。讨论了它们在结构上的相关性及可能的甜味机制,并对甜蛋白在食品工业及植物改良方面的应用进行了展望。     

单链莫内甜蛋白基因的合成及其植物表达载体的构建

目的:合成单链莫内甜蛋白基因,构建其植物表达载体。方法与结果:根据已报道的单链莫内甜蛋白的氨基酸序列及甜味机理,重新设计合成了全长294bp的莫内甜蛋白基因,其中单链莫内甜蛋白氨基酸序列中的Asp69(原AspA16)突变为Asn。利用DNA重组技术,将莫内甜蛋白基因克隆到植物表达载体pBl221中,构建了莫内甜蛋白基因的植物表达载体pBI221-monellin。结论:构建了莫内甜蛋白基因的植物表达载体,为转化园艺植物以改善其口感奠定了基础。     

不同生长周期的罗汉果鲜果中甜甙V和总黄酮含量变化规律研究

通过使用HPLC法对不同生长周期的罗汉果鲜果中罗汉果甜甙V和总黄酮的含量进行测定,总结出罗汉果中罗汉果甜甙V和总黄酮含量的变化规律,并对二者进行比较研究,结果表明坐果50d后,罗汉果甜甙Ⅴ的增加比较快,80d后,罗汉果甜甙Ⅴ的含量趋于稳定;随着生长周期的增加,罗汉果总黄酮的含量增加,40～50d中增长最快,坐果约50d后达到最高值,从60d开始总黄酮的含量迅速下降到20d水平,然后趋于稳定。     

罗汉果皂甙类成分代谢转化规律分析

目的:分析组织培养苗罗汉果皂甙类成分在果实成熟过程中的代谢转化规律,为罗汉果甜甙代谢关键酶的研究提供基础.方法:采用微波炉水煮法提取不同生长期罗汉果总甙,高相液相色谱(HPLC)分析各生长期罗汉果二糖甙(甙Ⅱ)、三糖甙(甙Ⅲ)和五糖甙(甙Ⅴ)的含量.结果:果龄10d的罗汉果中,能检测到甙Ⅱ(3 666.4/μg/100mg)及甙m(48.4ttg/100mg),甙Ⅴ检测不到;果龄50d时,能检测到甙Ⅴ(95.1μg/100mg)和高含量的甙Ⅲ(1213.8μg/100mg);随着果龄增长和果实逐渐成熟,低糖苦甙Ⅱ、甙Ⅲ含量逐渐减少,高糖甜甙Ⅴ含量逐渐升高.果龄70d时,苦甙Ⅱ、甙Ⅲ基本检测不到,而甜甙Ⅴ(1331.4μg/100mg)含量达到高水平.结论:罗汉果高糖甜甙可能是从低糖苦甙代谢转化而来.     

Recent advances in the study of Kaposi's sarcoma-associated herpesvirus replication and pathogenesis

It has now been over twenty years since a novel herpesviral genome was identified in Kaposi's sarcoma biopsies. Since then, the cumulative research effort by molecular biologists, virologists, clinicians, and epidemiologists alike has led to the extensive characterization of this tumor virus, Kaposi's sarcoma-associated herpesvirus(KSHV; also known as human herpesvirus 8(HHV-8)), and its associated diseases. Here we review the current knowledge of KSHV biology and pathogenesis, with a particular emphasis on new and exciting advances in the field of epigenetics. We also discuss the development and practicality of various cell culture and animal model systems to study KSHV replication and pathogenesis.     

The structure, reproduction and taxonomy of Vidalia and Osmundaria (Rhodophyta, Rhodomelaceae)

Comprises species occurring mostly in subtidal habitats in tropical, subtropical and warm-temperate areas of the world. An analysis of the type species, V. spiralis (Sonder) Lamouroux ex J. Agardh, a species from Australia, establishes basic characters for distinguishing species in the genus. These characters are (1) branching patterns of thalli, (2) flat blades that may be spiralled on their axis, (3) width of the blade, (4) primary or secondary derivation of sterile and fertile branchlets and (5) position of sterile and fertile branchlets on the thalli. Application of the latter two characters provides an important basic method for separation of species into three major groups. Osmundaria , a genus known only in southern Australia, was studied in relation to Vidalia , and its separation from the Vidalia assemblage is not accepted. Species of Vidalia therefore are transferred to the older genus name, Osmundaria. Two new species, Osmundaria papenfussii and Osmundaria oliveae are described from Natal. Confusion in the usage of the epithet, Vidalia fimbriala Brown ex Turner has been clarified, and Vidalia gregaria Falkenberg, described as an epiphyte on Osmundaria pro/ifera Lamouroux, is revealed to be young branches of the host, Osmundaria prolifera.     

New or rare chromosome counts in Artemisia L. (Asteraceae, Anthemideae) and related genera from Kazakhstan

Fifteen chromosome counts of six Artemisia taxa and one species of each of the genera Brachanthemum, Hippolytia, Kaschgaria, Lepidolopsis and Turaniphytum are reported from Kazakhstan. Three of them are new reports, two are not consistent with previous counts and the remainder are confirmations of very scarce (one to four) earlier records. All the populations studied have the same basic chromosome number, x = 9, with ploidy levels ranging from 2x to 6x. Some correlations between ploidy level, morphological characters and distribution are noted.     

肝癌中HBV和HCV基因和抗原的分布及意义

采用原位分子杂交方法检测HCV RNA及HBV X基因;采用免疫组织化学方法研究HCV核心抗原,非结构区C33c抗原及HBxAg在肝细胞肝癌中的定位及分布.结果表明(1)HCV RNA、HBV X基因在肝细胞肝癌组织检出率分别为40%(55/136)和82%(112/136).HCV RNA定位于癌细胞的胞浆内,阳性细胞呈散在、灶状及弥漫分布三种形式;HBV X基因在肝癌细胞中的分布呈胞浆型、核型及核浆型,阳性细胞也呈上述三种分布形式;(2)HCV C33c抗原、核心抗原在肝细胞肝癌中的阳性率为81%(133/164)及86%(141/164).C33c抗原定位于癌细胞及肝细胞的胞浆内;核心抗原既定位于癌细胞核中,又可定位于胞浆中.C33c抗原阳性细胞以灶状分布为主;而核心抗原阳性细     

Selection with two alleles and complete dominance

For a plant selection model with frequency-independent viabilities, fertilities and selfing rates, it is shown that apart from global fixation, for certain parameter combinations a protected polymorphism and facultative fixation (either allele may become fixed according to initial frequencies) may both occur. Facultative fixation requires different selling rates for the dominant and recessive type. Protection of the polymorphism requires resource allocation for male and female function. In this connection the problem of purely genetically caused population extinction is discussed.
For general frequency dependence and regular segregation, the chances for establishment of a completely recessive gene are compared to those of a completely dominant gene. It is proven that the process of establishment of the recessive gene, despite a fitness advantage, may be considerably endangered by drift effects if random mating prevails. The recessive gene may reach the same effectivity in establishment as a dominant gene, only if the recessive homozygote mates exclusively with its own type during the period of establishment.