铁钼辅因子

某些固氮生物(如棕色固氮菌)的变种,它们的固氮酶中铁蛋白有催化活性,但由于钼铁蛋白处于不活化状态,所以整个固氮酶不能显示出固氮活性,这种不能固氮的固氮酶可为从野生型固氮菌固氮酶钼铁蛋白中分离得到的物质(或因子)所活化或恢复固氮活性,此种活化因子叫钼铁辅因子。这种钼铁辅因子已从多种固氮生物中分离到,其分子量为1000～3000左右。按钼铁蛋白分子量为270,000计算,其中铝、铁、硫三种原     

固氮蓝藻与棕色固氮菌固氮酶组分的交叉互补功能

本文报告了藻菌之间固氮酶组分的交叉互补试验。初步结果证明：固氮蓝藻(Anabaena azotica水生686)的钼铁蛋白与棕色固氮菌(Azotobacter vinelandii)的铁蛋白之间存在着明显的互补功能。但这种蓝藻的铁蛋白在非细胞形态下很不稳定,易于失活。本实验为不同生理类型和不同进化程度的固氮生物之间固氮酶组分的交叉互补研究提供了新的资料。     

固氮蓝藻与棕色固氮菌固氮酶组分的交叉互补功能

本文报告了藻菌之间固氮酶组分的交叉互补试验。初步结果证明:固氮蓝藻(Anabacnaazotica水生686)的钼铁蛋白与棕色固氮菌(Azotobacter vinelandii)的铁蛋白之间存在着明显的互补功能。但这种蓝藻的铁蛋白在非细胞形态下很不稳定,易于失活。本实验为不同生理类型和不同进化程度的固氮生物之间固氮酶组分的交叉互补研究提供了新的资料。       

有催化活性的固氮酶二聚态钼铁蛋白

利用离子交换层析和凝胶过滤,第一次成功地从棕色固氮菌提取液中分离出接近电泳纯的能重组固氮酶活性的二聚态钼铁蛋白。它的分子量约为150,000,每分子含钼约0.5原子。当与铁蛋白重组固氮酶时,表现出相当高的活性。这个结果对固氮酶底物络合中心的结构提供了重要的启示,指出与目前较为流行的双钼多核中心相比,含单钼的多核中心至少同样是不可忽视的可能结构。     

光在钼影响蓝藻固氮中的作用

我们过去的工作曾指出,蓝藻及其离体异形胞的固氮是一个依赖于光的过程,光对蓝藻固氮酶的合成和活性有调节作用。此外,多年的生化研究也已确定,钼是包括蓝藻在内的一切固氮生物生长和参与固氮酶催化活性中心结构的必需与关键性的金属元素,它对钼铁蛋白有调控功能。这样,     

固氮酶

指固氮生物中对固定空气中分子氮并将其转变成氨起特殊催化功能的酶蛋白质。已从16种不同类型固氮生物中分离到固氮酶,它可分为两种独立的酶蛋白:(1)含钼和铁,称钼铁蛋白;(2)含铁,称铁蛋白。一般认为前者是络合和还原氮的中心,后者是电子活化中心。两者单独存在时不能固氮,只有合起来才能重组固氮活性。固氮酶(尤其是铁蛋白)对氧和摄氏零度左右的低温很敏感,易于失活。由于两种蛋白重组固氮活性时的确切比例尚不清楚,加上它们的均一制剂又未得到,所以对整个固氮酶的分子量还无法判断。目     

植物的共生固氮体系

氮是植物生命活动中不可缺少的重要元素之一。大气中的氮尽管为79％,但这种游离氮只有少数固氮细菌和蓝藻才能吸收利用,绿色植物却不能直接利用。这些细菌、蓝藻把大气中的游离氮固定转化为含氮化合物,成为植物所能吸收的氮,就称为生物固氮作用。固氮生物之所以能催化还原N2成NH3,是由于它含有固氮酶。固氮酶是一种结构复杂、功能特异的酶,由铁蛋白和钼铁蛋白组成。     

棕色固氮菌钼铁蛋白结晶及一些物理化学性质

获得了棕色固氮菌固氮酶钼铁蛋白的针状结晶,大小为2-2.5×25-65微米,成晶所要求的条件不是很严格的。SDS 电泳和氨基酸分析结果表明,钼铁蛋白分子量为250,000。只观察到一种类型亚单位。其中酸性氨基酸占优势。分子氧使针状晶体演变为发状晶丝,晶丝又密集成束。晶束可保存较长时间。氧使钼铁蛋白在电泳时形成高聚合态。       

不同底物与固氮酶及其钼铁蛋白相互作用的荧光光谱分析

 本文研究了不同底物(N_2,H_2,N_2O,NaN_3,C_2H_2)对棕色固氮菌固氮酶及其钼铁蛋白荧光光谱的影响。结果表明,上述底物均能络合在钼铁蛋白及固氮酶上,但络合程度不同,从而为固氮酶系统有多个不同的底物络合中心,底物络合中心在钼铁蛋白分子上,铁蛋白对钼铁蛋白有变构作用,提供了光谱学证据。     

纯化柱胞鱼腥藻(Anabaena cylindrca)固氮酶组份(铁蛋白)的厌氧制备电泳法

各种固氮生物的固氮酶对氧都很敏感,无论是制备固氮酶的组份Ⅰ(钼铁蛋白)或组份Ⅱ(铁蛋白),也无论采取什么方法(如DEAE-纤维素层析法、硫酸鱼精朊沉淀法、胶滤、制备凝胶电泳等等)都必需在严格厌氧条件下进行,铁蛋白对氧更加敏感,因此要获得较纯而又具活力的铁蛋白,其分离、纯化过程既要严格厌氧又要迅速。到目前为止,仅红螺菌(Rhodospirillum rubrum)和棕色     

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.