基于居民生态认知的非使用价值支付意愿空间分异研究——以三江平原湿地为例

在WTP距离衰减性研究基础上,将菲什拜因理论与条件价值法相结合,假设个人对于物品的认知在空间上并不是均衡分布的,不同空间内的受访者的支付意愿存在差异,以三江平原湿地生态系统为应用对象,将样本分为核心区、辐射区、外围区,采用双边界二分式CVM,探讨受访者对三江平原湿地生态环境保护的支付意愿水平及支付意愿的影响因素,建立基于居民生态认知的支付意愿空间分异模型。计算得到核心区、辐射区、外围区居民平均支付意愿分别为142.23元人-1a-1、105.01元人-1a-1、77.62元/人,总体呈递减趋势,验证了距离、认知和WTP之间相关性。研究结果表明,通过空间视角将居民的认知程度纳入支付意愿的计算,能提高CVM在环境价值评估应用中的有效性及可靠性。研究结论将为政府相关政策的制定和决策提供参考依据。     

Fast conformational exchange between the sulfur-free and persulfide-bound rhodanese domain of E. coli YgaP

Rhodanese domains are abundant structural modules that catalyze the transfer of a sulfur atom from thiolsulfates to cyanide via formation of a covalent persulfide intermediate that is bound to an essential conserved cysteine residue. In this study, the three-dimensional structure of the rhodanese domain of YgaP from Escherichia coli was determined using solution NMR. A typical rhodanese domain fold was observed, as expected from the high homology with the catalytic domain of other sulfur transferases. The initial sulfur-transfer step and formation of the rhodanese persulfide intermediate were monitored by addition of sodium thiosulfate using two-dimensional ¹H–¹⁵N correlation spectroscopy. Discrete sharp signals were observed upon substrate addition, indicting fast exchange between sulfur-free and persulfide-intermediate forms. Residues exhibiting pronounced chemical shift changes were mapped to the structure, and included both substrate binding and surrounding residues.     

产气肠杆菌EAM-Z1尿苷磷酸化酶的分离纯化及性质研究

从产气肠杆菌 (Enterobacteraerogenes)突变株EAM Z1中分离出一种具有较高转移酶活性的尿苷磷酸化酶 (UPase)。经测定这种Upase的分子量为 1 2 .8× 1 0 4,亚基分子量为 4 .3×1 0 4,由 3个同型亚基组成。N端氨基酸序列为 :MRMVDLIATKRDGGE。等电点为 4 .46。对尿苷的Km为 0 .2 9mmol L。酶反应的最适pH为 7.8,最适温度为 50℃。该酶能磷酸化尿苷、胸苷、5 氟尿苷、2′ 脱氧 5 氟尿苷及尿嘧啶 β D 阿拉伯呋喃糖 ,且具有较高的转移酶活性 ,能将尿苷和 5 氟尿嘧啶转化成 5 氟尿苷 (一种抗癌药物的中间体 ) ,其转化率为 47%。该酶的这些特性对于酶法合成核苷类抗肿瘤药物和抗病毒药物是十分有用的。     

Rac1 modulates sphingosine 1-phosphate-mediated activation of phosphoinositide 3-kinase/Akt signaling pathways in vascular endothelial cells

Sphingosine 1-phosphate (S1P) is a platelet-derived sphingolipid that activates G protein-coupled S1P receptors and initiates a broad range of responses in vascular endothelial cells. The small GTPase Rac1 is implicated in diverse S1P-modulated cellular responses in endothelial cells, yet the molecular mechanisms involved in S1P-mediated Rac1 activation are incompletely understood. We studied the pathways involved in S1P-mediated Rac1 activation in bovine aortic endothelial cells (BAEC) and found that S1P-induced Rac1 activation is impaired following chelation of G protein betagamma subunits by transfection of betaARKct. Treatment with the Src tyrosine kinase inhibitor PP2 completely attenuated S1P-mediated Rac1 activation; however, pretreatment of BAEC with wortmannin, an inhibitor of phosphoinositide (PI) 3-kinase, had no effect on Rac1 activation while completely blocking S1P-induced Akt phosphorylation. We used Rac1-specific small interfering RNA (siRNA) duplexes to "knock down" endogenous Rac1 expression and found that siRNA-mediated Rac1 knockdown significantly impaired basal as well as S1P-induced phosphorylation of protein kinase Akt, as well as several downstream targets of Akt including endothelial nitric-oxide synthase and glycogen synthase kinase 3beta. By contrast, S1P-induced phosphorylation of the mitogen-activated protein kinases ERK1/2 was unperturbed by siRNA-mediated Rac1 knockdown. We found that overexpression of the Rac1 guanine nucleotide exchange factor (GEF) Tiam1 markedly enhanced Rac1 activity, whereas a dominant negative Tiam1 mutant significantly attenuated S1P-mediated Rac1 activation. Taken together, these studies identify G protein betagamma subunits, Src kinase and the GEF Tiam1 as upstream modulators of S1P-mediated Rac1 activation, and establish a central role for Rac1 in S1P-mediated activation of PI 3-kinase/Akt/endothelial nitric-oxide synthase signaling in vascular endothelial cells.     

Heritable alteration in DNA methylation pattern occurred specifically at mobile elements in rice plants following hydrostatic pressurization

Intrinsic DNA methylation pattern is an integral component of the epigenetic network in many eukaryotes. Exploring the extent to which DNA methylation patterns can be altered under a specific condition is important for elucidating the biological functions of this epigenetic modification. This is of added significance in plants wherein the newly acquired methylation patterns can be inherited through organismal generations. We report here that DNA methylation patterns of mobile elements but not of cellular genes were specifically altered in rice plants following hydrostatic pressurization. This was evidenced by methylation-sensitive gel-blot analysis, which showed that 10 out of 10 studied low-copy transposons and retrotransposons manifested methylation alteration in at least one of the 8 randomly chosen pressure-treated plants, whereas none of the 16 studied low-copy cellular genes showed any change. Both gel-blotting and genome-wide fingerprinting indicated that the methylation alteration in mobile elements was not accompanied by a general genetic instability. Progeny analysis indicated retention of the altered methylation patterns in most progeny plants, underscoring early occurrence of the alterations, and their faithful epigenetic inheritance.     

Long-term high-fat diet induces pancreatic injuries via pancreatic microcirculatory disturbances and oxidative stress in rats with hyperlipidemia

Stromal cell-derived factor 1 (CXCL12) is an angiogenic chemokine that is believed to act solely via its cognate receptor CXCR4. Evidence is now provided for the existence of a different CXCL12 binding and signaling receptor on endothelial cells. Bovine aortic endothelial cells (BAECs) strongly expressed CXCR4 and exhibited high binding capacity for fluorescently labeled CXCL12. However, CXCL12 binding was not correlated with the CXCR4 expression level and was virtually unaffected by the specific CXCR4 antagonists AMD3100 or T22. Similar observations were made in endothelial cells of mouse and human origin. Also, AMD3100 failed to block CXCL12 internalization and CXCL12-induced intracellular signal transduction via extracellular signal-regulated kinases 1/2 in BAECs. In contrast, CXCL12 binding and signaling were almost completely inhibited by the CXCR4 antagonist in T-lymphoid SupT1 cells. Together, our data point to the existence of an additional receptor through which CXCL12 exerts its biological effects in endothelial cells.     

我国东北森林土壤动物生态学研究现状与展望

土壤动物在生态系统养分循环和能量流动中起到重要的作用。近年来土壤动物生态学研究已成为当前生态学研究的热点与前沿领域。土壤动物生态学研究在国际上已有60多年的历史, 但在我国真正意义上的土壤动物生态学研究起始于20世纪70年代末东北长白山的研究。本文概述了东北森林土壤动物生态学研究的三个阶段, 并重点从以下方面总结了近10年的研究现状与进展: 土壤动物分布格局及多样性、土壤动物对环境因子的响应、土壤动物在生态系统中的功能作用研究。本文可为进一步拓展东北森林土壤动物生态学研究并为我国其他地区深入开展土壤动物生态学研究提供参考。未来东北森林土壤动物生态学研究应该关注: 土壤动物与微生物交互作用、土壤动物对全球变化的响应、地上与地下生态系统的交互作用以及分子生物学技术在土壤生物研究中的应用。