PsbY, a novel manganese-binding, low-molecular-mass protein associated with photosystem II

We describe two related manganese-binding polypeptides with L-arginine metabolizing enzyme activity that can be detected as distinct components (designated PsbY-A1 and PsbY-A2, previously called L-AME) in membranes containing Photosystem II (PS II) from spinach. The polypeptides are bitopic and appear to exist in a heterodimeric form, but only in the chlorophyll a/b lineage of plants. Both proteins are encoded in the nucleus. In spinach and in Arabidopsis thaliana they are both derived from a single-copy gene (psbY) that is translated into a precursor polyprotein of approximately 20 kDa. The processing of the polyprotein is complex and includes at least four cleavage steps. Both polypeptides are exposed N-terminally to the lumenal and C-terminally to the stromal face of the thylakoid membrane. Received: 9 June 1998 / Accepted: 9 July 1998     

厚壁毛竹快速高生长期竹秆ATP酶超微细胞化学定位

采用电镜细胞化学技术对厚壁毛竹(Phyllostachys edulis ‘Pachyloen’)快速高生长期竹秆节间的伸长发育过程（包括：分生细胞期、伸长初期、快速伸长期和成熟期四个阶段）进行ATP酶超微细胞化学定位,以揭示竹秆节间快速伸长的细胞学基础。结果表明：分生细胞期,细胞质膜、核膜、细胞器膜系统上等均有很强的ATP酶活性。伸长初期,节间上部基本组织细胞质膜上ATP酶活性较强,且短细胞质膜上的ATP酶活性更强,节间基部各细胞均未观察到ATP酶活性。快速伸长期,节间基部基本组织ATP酶活性较节间上部高,细胞质膜、运输小泡膜、胞间隙及胞间连丝上均有ATP酶活性。成熟期,仅节间上部基本组织质膜上有较弱的ATP酶活性。ATP酶在节间伸长过程中主要参与新细胞壁物质的分泌和共质体运输,促进新细胞壁的形成,晶体和淀粉粒体外膜上ATP酶活性的存在表明其具有贮存物质的作用。节隔缺失节的节间基部未观察到ATP酶活性,节部韧皮结细胞ATP酶活性较高,节隔的缺失引起节部与节间与物质运输有关结构的变化,进而影响节间伸长生长。     

1,3-Bis[N-sulfonyl-(1R,2S)-1,3-diphenyl-2-aminopropanol]benzene: an excellent ligand for titanium-catalyzed asymmetric AlPh3(THF) additions to aldehydes

Asymmetric AlPh(3) (THF) additions to a wide variety of aldehydes catalyzed by a titanium catalyst of 20 mol % 1,3-bis[N-sulfonyl-(1R,2S)-1,3-diphenyl-2-aminopropanol]benzene (1) are reported. The catalytic system works excellently for aromatic aldehydes bearing either an electron-donating or an electron-withdrawing substituent on the aromatic ring to afford secondary diaryl alcohols in excellent isolated yields of >or=95% and excellent enantioselectivities of >or=94% ee. The phenyl addition to cinnamaldehyde or 2-furylaldehyde gave corresponding secondary alcohols in 85% and 95% ee, respectively. For aliphatic aldehydes, increasing enantioselectivities of the addition products in terms of increasing steric sizes of aldehydes are observed, and this trend goes from the linear 1-pentanal (87% ee), the secondary cyclohexylaldehyde (95% ee) or the 2-methylpropanal (97% ee), to the tertiary 2,2-dimethylpropanal (99% ee).     

A barrier-only boundary element delimits the formation of facultative heterochromatin in Drosophila melanogaster and vertebrates

Formation of facultative heterochromatin at specific genomic loci is fundamentally important in defining cellular properties such as differentiation potential and responsiveness to developmental, physiological, and environmental stimuli. By the nature of their formation, heterochromatin and repressive histone marks propagate until the chain reaction is broken. While certain active promoters can block propagation of heterochromatin, there are also specialized DNA elements, referred to as chromatin barriers, that serve to demarcate the boundary of facultative heterochromatin formation. In this study, we identified a chromatin barrier that specifically limits the formation of repressive chromatin to a distal enhancer region so that repressive histone modifications cannot reach the promoter and promoter-proximal enhancer regions of reaper. Unlike all of the known boundary elements identified for Drosophila melanogaster, this IRER (irradiation-responsive enhancer region) left barrier (ILB) does not exhibit enhancer-blocking activity. Not only has the ILB been conserved in different Drosophila species, it can also function as an effective chromatin barrier in vertebrate cells. This suggests that the mechanism by which it functions to spatially restrict the formation of repressive chromatin marked by trimethylated H3K27 has also been conserved widely during evolution.     

自然降雨下黄土丘陵区草灌植物垂直覆盖结构的减流减沙效应

黄土高原是我国水土流失和生态环境问题最为严重的地区之一,植被恢复是防治水土流失的重要措施。植物垂直覆盖结构包括地上冠层、地表枯落物和地下根系,各组分具有不同的水土保持作用,是研究植被与水土流失关系的基本单元。目前,关于植物垂直覆盖结构不同组分对土壤侵蚀影响的研究主要是基于人工模拟降雨,缺少自然降雨条件下不同植物的垂直覆盖结构对产流、产沙和入渗等多过程影响的系统研究。本研究以黄土丘陵区典型的草本(须芒草)、半灌木(铁杆蒿)和灌木(绣线菊)为研究对象,每种植物进行三种处理(自然状态、去除枯落物和仅留根系)以及裸地对照,观测2015—2016年降雨事件的产流产沙量和入渗量,分析植物不同垂直覆盖结构的减流减沙效益及其相对贡献。结果表明:三种植物均具有较好的减流(45.9%—73.2%)、减沙效益(87.5%—94.6%)和增加入渗作用(4.7%—10.8%),灌木的减流效果(73.2%)显著高于草本(45.9%)和半灌木(63.5%),但三种植物间的减沙效益没有显著性差异。冠层的减流作用最大,贡献率接近一半(48%—50%),草本枯落物的减流贡献率与根系基本一致,而半灌木和灌木枯落物的减流贡献...     

特异腐质霉角质酶-锚定肽融合蛋白的特性及在处理再生纸胶黏物中的应用

随着森林木材资源的减少,废纸回收利用越来越受到人们的重视.然而,废纸回收利用过程中产生的胶黏物会对再生纸的生产造成严重影响.生物法控制胶黏物主要是通过酶断裂胶黏物组分之间的酯键,防止胶黏物的絮凝,具有高效、专一、无污染等优势.角质酶是一种丝氨酸酯酶,可降解胶黏物中的部分成分.相关研究表明,锚定肽tachystatin ...