胞外ATP的作用,来源和命运

胞外ＡＴＰ（三磷酸腺苷）浓度的改变,影响许多重要的生理功能,诸如神经递质作用、上板凝聚、篾这紧张、心脏功能肉收缩等。胞外ＡＴＰ作为递质直接影响神经效应器接点和／调制其它神经递质以及通过第二信使调节细胞活动,都是由膜上不同的ＡＴＰ受体或激活的离子通道介导的。本文从胞外ＡＴＰ的递质作用的发现与确证,胞外ＡＴＰ的来源、ＡＴＰ的受体、ＡＴＰ介导的反应及包外ＡＴＰ的降解等几方面对胞外ＡＴＰ研究的进展作一综述     

Identification of Src, Fyn, and Lyn SH3-binding proteins: implications for a function of SH3 domains.

Src homology 3 (SH3) domains mediate protein-protein interactions necessary for the coupling of cellular proteins involved in intracellular signal transduction. We previously established solution-binding conditions that allow affinity isolation of Src SH3-binding proteins from cellular extracts (Z. Weng, J. A. Taylor, C. E. Turner, J. S. Brugge, and C. Seidel-Dugan, J. Biol. Chem. 268:14956-14963, 1993). In this report, we identified three of these proteins: Shc, a signaling protein that couples membrane tyrosine kinases with Ras; p62, a protein which can bind to p21rasGAP; and heterogeneous nuclear ribonucleoprotein K, a pre-mRNA-binding protein. All of these proteins contain proline-rich peptide motifs that could serve as SH3 domain ligands, and the binding of these proteins to the Src SH3 domain was inhibited with a proline-rich Src SH3 peptide ligand. These three proteins, as well as most of the other Src SH3 ligands, also bound to the SH3 domains of the closely related protein tyrosine kinases Fyn and Lyn. However, Src- and Lyn-specific SH3-binding proteins were also detected, suggesting subtle differences in the binding specificity of the SH3 domains from these related proteins. Several Src SH3-binding proteins were phosphorylated in Src-transformed cells. The phosphorylation of these proteins was not detected in cells transformed by a mutant variant of Src lacking the SH3 domain, while there was little change in tyrosine phosphorylation of other Src-induced phosphoproteins. In addition, the coprecipitation of v-Src with two tyrosyl-phosphorylated proteins with M(r)s of 62,000 and 130,000 was inhibited by incubation with a Src SH3 peptide ligand, suggesting that the binding of these substrate proteins is dependent on interactions with the SH3 domain. These results strongly suggest a role for the Src SH3 domain in the recruitment of substrates to this protein tyrosine kinase, either through direct interaction with the SH3 domain or indirectly through interactions with proteins that bind to the SH3 domain.     

Hydrogen bond interactions of G proteins with the guanine ring moiety of guanine nucleotides.

We have utilized Raman difference spectroscopy to investigate hydrogen bonding interactions of the guanine moiety in guanine nucleotides with the binding site of two G proteins, EF-Tu (elongation factor Tu from Escherichia coli) and the c-Harvey ras protein, p21 (the gene product of the human c-H-ras proto-oncogene). Raman spectra of proteins complexed with GDP (guanosine 5' diphosphate), IDP (inosine 5' diphosphate), 6-thio-GDP, and 6-18O-GDP were measured, and the various difference spectra were determined. These were compared to the difference spectra obtained in solution, revealing vibrational features of the nucleotide that are altered upon binding. Specifically, we observed significant frequency shifts in the vibrational modes associated with the 6-keto and 2-amino positions of the guanine group of GDP and IDP that result from hydrogen bonding interactions between these groups and the two proteins. These shifts are interpreted as being proportional to the local energy of interaction (delta H) between the two groups and protein residues at the nucleotide binding site. Consistent with the tight binding between the nucleotides and the two proteins, the shifts indicate that the enthalpic interactions are stronger between these two polar groups and protein than with water. In general, the spectral shifts provide a rationale for the stronger binding of GDP and IDP with p21 compared to EF-Tu. Despite the structural similarity of the binding sites of EF-Tu and p21, the strengths of the observed hydrogen bonds at the 6-keto and 2-amino positions vary substantially, by up to a factor of 2.(ABSTRACT TRUNCATED AT 250 WORDS)     

小鼠胚胎及生后发育的肾上腺皮质的组织学与组织化学研究

胚龄１３日小鼠肾上腺结构尚未形成,在肾附近可见两群细胞。１５日两群细胞融合,呈一新月形小体,外包被膜,内含两类细胞,一类胞体较大,染色较深,另一类胞体较小,染色浅。１７日,胞体大染色深的细胞形成团索状,发育成皮质细胞;另一类细胞则迁移至中央,形成髓质。组织化学研究显示,胎龄１５日及以后的肾上腺皮质细胞３β－羟甾体脱氢酶（３β－ＨＳＤＨ）、脂类、酸性磷酸酶（ＡＣＰ）、亮氨酸氨基肽酶（ＬＮＡｓｅ）均为阳性。以上一些酶活性的出现提示１５日及其后胚鼠,生后１～６０天小鼠的肾上腺皮质都有分泌甾体激素之功能。     

Purification and characterization of the Upf1 protein: a factor involved in translation and mRNA degradation.

mRNA degradation is an important control point in the regulation of gene expression and has been shown to be linked to the process of translation. One clear example of this linkage is the observation that nonsense mutations in a gene can accelerate the decay of the corresponding mRNA. In the yeast Saccharomyces cerevisiae, the product of the UPF1 gene, harboring zinc finger, NTP hydrolysis, and helicase motifs, was shown to be a trans-acting factor in this decay pathway. A UPF1 gene disruption results in stabilization of nonsense-containing mRNAs and leads to a nonsense suppression phenotype. As a first step toward understanding the molecular and biochemical mechanism of nonsense-mediated mRNA decay, we have purified Upf1p from a yeast extract and characterized its nucleic acid-dependent NTPase activity, helicase activity, and nucleic acid binding properties. The results presented in this paper demonstrate that Upf1p contains both RNA- and DNA-dependent ATPase activities and RNA and DNA helicase activities. In the absence of ATP, Upf1p binds to single-stranded RNA or DNA, whereas hydrolysis of ATP facilitates its release from single-stranded nucleic acid. Based on these results, the role of Upf1p's biochemical activities in mRNA decay and translation are discussed.     

鸡冠花种子营养成分的研究

鸡冠花种子可供食用和药用。作者采用常规方法系统地分析测定了其营养成分,并和一些谷类,豆类食物进行了比较。结果显示,鸡冠花种子含各种营养成分:蛋白质、脂肪、碳水化合物、膳食纤维、氨基酸、维生素、无机元素等,不仅含量丰富且高于谷类。这为开发利用鸡冠花种子提供了科学依据。     

Selenium-rich dissolved organic matter determines selenium uptake in wheat grown on Low-selenium arable land soils

Aims

The study aimed to find soil parameters that are best related to Se plant uptake for low Se soils with predominantly organic Se, and to explore the mechanisms that control Se bioavailability in the soils under study.

Methods

A pot experiment using nineteen soil samples taken from different fields of arable land (potato fields) in the Netherlands was conducted on summer wheat (Triticum aestivum L.). Selenium in wheat shoots and soil parameters, including basic soil properties, C:N ratio, inorganic selenite content, and Se and organic C in different soil extractions (0.01 M CaCl₂, 0.43 M HNO₃, hot water, ammonium oxalate, aqua regia) were analysed. Regression analysis was performed to identify soil parameters that determine Se content in wheat shoots.

Results

The regression model shows that Se:DOC ratio in 0.01 M CaCl₂ soil extraction explained about 88 % of the variability of Se uptake in wheat shoots. Selenium uptake increased with Se:DOC ratio in CaCl₂ extraction, which can be interpreted as a measure of the content of soluble Se-rich organic molecules. Selenium:DOC ratio in CaCl₂ extraction and Se uptake increased towards higher soil pH and lower soil C:N ratio. The soil C:N ratio is also negatively correlated to Se:organic C ratio in other extractions (0.43 M HNO₃, hot water, ammonium oxalate, aqua regia), indicating that at low soil C:N ratio soil organic matter is richer in Se. Contrarily, the soil pH is positively and strongly correlated to Se:organic C ratio in CaCl₂ and hot water extractions, but only weakly correlated to Se:organic C ratio in other extractions.

Conclusions

Selenium-rich dissolved organic matter is the source of bioavailable Se in low Se soils with predominantly organic Se. The soil pH and quality of soil organic matter (i.e. soil C:N ratio) are the main soil properties determining Se bioavailability in these soil types.

     

The influence of NBD fluorescent probe on model membranes containing POPC and DPPC

To investigate the effect of fluorescent probe on the properties of membranes, we studied model membranes composed of 1,2- dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1-palmitoyl 2-oleoyl-sn-glycero-3-phosphocholine (POPC) in the presence and absence of fluorescent probe. The morphology of giant unilamellar vesicles (GUVs) has been observed as a function of temperature and composition by fluorescence microscopy using NBD-DOPE or C₆-NBD-PC as the probe. The phase behavior of model membranes containing no fluorescent probe was investigated by ²H-NMR spectroscopy. We found that the bright phase observed on GUVs was the fluid phase enriched in POPC and the dark phase was the gel phase enriched in DPPC. NBD-DOPE and C₆-NBD-PC preferentially participated in the fluid-phase domains when GUVs were in the gel?+?fluid phase coexistence. Inclusion of both fluorescent probes (1?mol%) lowered the transition temperature of POPC/DPPC membranes. In addition, C₆-NBD-PC exhibited a stronger effect than NBD-DOPE, which was considered to be associated with the structures of fluorescent molecules.     

水肥耦合效应对楸树苗期叶片净光合速率和SPAD值的影响

以楸树无性系004-1苗木为研究对象,采用三因素五水平二次回归通用旋转组合设计,通过盆栽试验测定不同处理下楸树苗木叶片净光合速率(Pn)和SPAD值,并建立其与土壤水分(W)、施氮量(N)和施磷量(P)回归模型,分析土壤水分、施氮量和施磷量的主因子、单因素及耦合效应对楸树苗木叶片Pn和SPAD值的影响。研究结果表明:(1)W和N对楸树苗木叶片Pn和SPAD均有显著正效应,并且N主效应大于W,而施磷量主效应不显著;(2)单因素效应分析结果表明,楸树苗木叶片Pn和SPAD值随着N的增加均呈现出先增大后减小的变化趋势,与N类似,叶片Pn和SPAD值对W的响应曲线也呈现出类似的"抛物线式"变化趋势;(3)W×N对楸树苗木Pn和SPAD值均存在显著耦合正效应,但Pn和SPAD值与W×N的响应曲面关系图有所不同:随着土壤水分和施氮量的同时增加,叶片Pn逐渐增加,而叶片SPAD值呈现出先增加后减小的变化趋势;(4)楸树苗木叶片Pn与SPAD值呈现出极显著正相关关系(P0.0001)。总体而言,与土壤水分和施磷量相比,楸树生长更容易受土壤施氮量限制,此外,通过合理水肥配施措施,能一定程度提高楸树苗木的光合生产力和叶片SPAD值。