阔叶树的叶形曲线方程：—适于叶面积计算的数学模型

树木的叶形可以看作一个平面几何图形。这种几何图形可用解析方程给予表达,我们把这种解析方程称为叶形曲线方程。由于叶形是一个左右对称,而上下不对称的图形,也就是说叶的最宽处绝大多数不在叶的中部,少数在     

Effects of circadian rhythms of fluctuating temperature on growth and biochemical composition of <Emphasis Type="Italic">Ulva pertusa</Emphasis>

The marcoalga Ulva pertusa was cultured under (20 ± 2)°C, (20 ± 4)°C, (20 ± 6)°C, (20 ± 8)°C and (20 ± 10)°C circadian rhythms of fluctuating temperature conditions, and constant temperature of 20°C was used as the control. The growth rate of macroalga at (20 ± 2)°C, (20 ± 4)°C and (20 ± 6)°C were significantly higher than that at constant temperature of 20°C, while growth rate at (20 ± 8)°C and (20 ± 10)°C were significantly lower than that at constant temperature of 20°C. The growth rate of macroalga was a quadratic function of the thermal amplitude. Such a growth model can be described by G = β ₀ + β ₁(TA) + β ₂(TA)², where G represents the relative growth rate, TA is thermal amplitude in degree Celsius, β ₀ is the intercept on the G axis, and β ₁ and β ₂ are the regression coefficients. The optimal thermal amplitude for the growth of thallus at mean temperature of 20°C was estimated to be ± 3.69°C. Analysis of biochemical composition at the final stages of thaulls growth revealed that diel fluctuating temperature caused various influences (P < 0.05). The content of chlorophyll, protein and total solute carbohydrate at (20 ± 2)°C and (20 ± 4)°C were slightly higher than those at constant temperature of 20°C, however no statistically significant differences were found among them (P > 0.05). While osmolytes (total solute carbohydrate and free proline) at (20 ± 10)°C were significantly higher than that at 20°C (P < 0.05). Therefore, more chlorophyll and carbohydrate production might account for the enhancement in the growth of macroalga at the diel fluctuating temperatures in the present study. Handling editor: S. M. Thomaz     

Simultaneous determination of metformin and rosiglitazone in human plasma by liquid chromatography/tandem mass spectrometry with electrospray ionization: application to a pharmacokinetic study

A selective and sensitive high performance liquid chromatography-electrospray ionization-tandem mass spectrometry (ESI-MS/MS) method for simultaneous determination of metformin and rosiglitazone in human plasma using phenformin as internal standard (IS) has been first developed and validated. Plasma samples were precipitated by acetonitrile and the analytes were separated on a prepacked Phenomenex Luna 5u CN 100A (150 mm x 2.0 mm I.D.) column using a mobile phase comprised of methanol:30 mM ammonium acetate pH 5.0 (80:20, v/v) delivered at 0.2 ml/min. Detection was performed on a Finnigan TSQ triple-quadrupole tandem mass spectrometer in positive ion selected reaction monitoring (SRM) mode using electrospray ionization. The ion transitions monitored were m/z 130.27-->71.11 for metformin, m/z 358.14-->135.07 for rosiglitazone and m/z 206.20-->105.19 for the IS. The standard curves were linear (r(2)>0.99) over the concentration range of 5-3000 ng/ml for metformin and 1.5-500 ng/ml for rosiglitazone with acceptable accuracy and precision, respectively. The within- and between-batch precisions were less than 15% of the relative standard deviation. The limit of detection (LOD) of both metformin and rosiglitazone was 1 ng/ml. The method described is precise and sensitive and has been successfully applied to the study of pharmacokinetics of compound metformin and rosiglitazone capsules in 12 healthy Chinese volunteers.     

Homologs of eukaryotic Ras superfamily proteins in prokaryotes and their novel phylogenetic correlation with their eukaryotic analogs

Ras superfamily proteins are key regulators in a wide variety of cellular processes. Previously, they were considered to be specific to eukaryotes, and MglA, a group of obviously different prokaryotic proteins, were recognized as their only prokaryotic analogs or even ancestors. Here, taking advantage of quite a current accumulation of prokaryotic genomic databases, we have investigated the existence and taxonomic distribution of Ras superfamily protein homologs in a much wider prokaryotic range, and analyzed their phylogenetic correlation with their eukaryotic analogs. Thirteen unambiguous prokaryotic homologs, which possess the GDP/GTP-binding domain with all the five characteristic motifs of their eukaryotic analogs, were identified in 12 eubacteria and one archaebacterium, respectively. In some other archaebacteria, including four methanogenic archaebacteria and three Thermoplasmales, homologs were also found, but with the GDP/GTP-binding domains not containing all the five characteristic motifs. Many more MglA orthologs were identified than in previous studies mainly in delta-proteobacteria, and all were shown to have common unique features distinct from the Ras superfamily proteins. Our phylogenetic analysis indicated eukaryotic Rab, Ran, Ras, and Rho families have the closest phylogenetic correlation with the 13 unambiguous prokaryotic homologs, whereas the other three eukaryotic protein families (SRbeta, Sar1, and Arf) branch separately from them, but have a relatively close relationship with the methanogenic archaebacterial homologs and MglA. Although homologs were identified in a relative minority of prokaryotes with genomic databases, their presence in a relatively wide variety of lineages, their unique sequence characters distinct from those of eukaryotic analogs, and the topology of our phylogenetic tree altogether do not support their origin from eukaryotes as a result of lateral gene transfer. Therefore, we argue that Ras superfamily proteins might have already emerged at least in some prokaryotic lineages, and that the seven eukaryotic protein families of the Ras superfamily may have two independent prokaryotic origins, probably reflecting the 'fusion' evolutionary history of the eukaryotic cell.     

Diversity and Biogeography of Rhizobia Isolated from Root Nodules of <Emphasis Type="Italic">Glycine max</Emphasis> Grown in Hebei Province,China

A total of 215 rhizobial strains were isolated and analyzed with 16S rRNA gene, 16S–23S intergenic spacer, housekeeping genes atpD, recA, and glnII, and symbiotic genes nifH and nodC to understand the genetic diversity of soybean rhizobia in Hebei province, China. All the strains except one were symbiotic bacteria classified into nine genospecies in the genera of Bradyrhizobium and Sinorhizobium. Surveys on the distribution of these rhizobia in different regions showed that Bradyrhizobium japonicum and Bradyrhizobium elkanii strains were found only in neutral to slightly alkaline soils whereas Bradyrhizobium yuanmingense, Bradyrhizobium liaoningense-related strains and strains of five Sinorhizobium genospecies were found in alkaline–saline soils. Correspondence and canonical correspondence analyses on the relationship of rhizobial distribution and their soil characteristics reveal that high soil pH, electrical conductivity, and potassium content favor distribution of the B. yuanmingense and the five Sinorhizobium species but inhibit B. japonicum and B. elkanii. High contents of available phosphorus and organic matters benefit Sinorhizobium fredii and B. liaoningense-related strains and inhibit the others groups mentioned above. The symbiotic gene (nifH and nodC) lineages among B. elkanii, B. japonicum, B. yuanmingense, and Sinorhizobium spp. were observed in the strains, signifying that vertical gene transfer was the main mechanism to maintain these genes in the soybean rhizobia. However, lateral transfer of symbiotic genes commonly in Sinorhizobium spp. and rarely in Bradyrhizobium spp. was also detected. These results showed the genetic diversity, the biogeography, and the soil determinant factors of soybean rhizobia in Hebei province of China.     

固氮树种在混交林中的作用研究Ⅲ.固氮树种凋落物分解及N的释放

研究了１１种固氮和非固氮树种凋落物分解及可利用态Ｎ的释放．结果表明,固氮树木凋落物中Ｎ的生物分解系数、落叶分解过程中干重的损失率及有效态氮的释放分别比非固氮树种高出１．３、１．５和８．２倍．     

Site-specific solvent exposure analysis of a membrane protein using unnatural amino acids and 19F nuclear magnetic resonance

Membrane proteins play an essential role in cellular metabolism, transportation and signal transduction across cell membranes. The scarcity of membrane protein structures has thus far prevented a full understanding of their molecular mechanisms. Preliminary topology studies and residue solvent exposure analysis have the potential to provide valuable information on membrane proteins of unknown structure. Here, a (19)F-containing unnatural amino acid (trimethylfluoro-phenylalanine, tfmF) was applied to accomplish site-specific (19)F spin incorporation at different sites in diacylglycerol kinase (DAGK, an Escherichia coli membrane protein) for site-specific solvent exposure analysis. Due to isotope effect on (19)F spins, a standard curve for (19)F-tfmF chemical shifts was drawn for varying solvent H(2)O/D(2)O ratios. Further site-specific (19)F solvent isotope shift analysis was conducted for DAGK to distinguish residues in water-soluble loops, interfacial areas or hydrophobic membrane regions. This site-specific solvent exposure analysis method could be applied for further topological analysis of other membrane proteins.     

过表达Lin28a/Lin28b对let-7家族活性的影响

研究在HeLaS3细胞中过表达Lin28a/Lin28b对let-7家族miRNA表达水平和活性的影响。首先,构建Lin28a和Lin28b的表达载体pAAV2neo-Lin28a和pAAV2neo-Lin28b,分别转染HeLaS3细胞并筛选获得Lin28a和Lin28b的稳定表达细胞株HeLaS3/pAAV2neo-Lin28a和HeLaS3/pAAV2neo-Lin28b。然后,以pAAV2neo-Gluc-(Fluc)为基本骨架,构建并获得检测let-7家族miRNA活性的8种质粒型载体,并包装为相应的重组腺相关病毒(Recombinant adeno-associated virus,rAAV),作为检测miRNA靶序列介导的转录后抑制活性的传感器,命名为Asensor。在此基础上,以HeLaS3细胞为对照,用Western blot检测HeLaS3/pAAV2neo-Lin28a和HeLaS3/pAAV2neo-Lin28b细胞中Lin28a和Lin28b表达水平,用QRT-PCR测定let-7家族各成员表达水平,用Asensor检测let-7家族各成员活性。Western blot结果显示,HeLaS3/pAAV2neo-Lin28a和HeLaS3/pAAV2neo-Lin28b均能有效地表达Lin28a和Lin28b蛋白;QRT-PCR检测结果显示,相比于HeLaS3细胞,HeLaS3/pAAV2neo-Lin28a细胞中let-7家族各成员表达水平都下降(除let-7e外),但不同成员下降幅度存在差异;Asensor检测结果显示,let-7家族所有成员活性水平都下降,但不同成员下降幅度也存在差异,且同一成员活性水平与表达水平及其下降趋势也不一致。相比于HeLaS3细胞,HeLaS3/pAAV2neo-Lin28b细胞中let-7家族成员的表达和活性水平均明显下降,但表达水平的下降幅度比HeLaS3/pAAV2neo-Lin28a细胞大,而活性的下降幅度却与之相近。本研究建立了一种检测和比较miRNA靶序列介导的转录后抑制活性的方法,首次研究了过表达Lin28a和Lin28b对细胞中的let-7家族miRNA活性影响,并发现Lin28a和Lin28b对let-7家族miRNA表达水平的影响和对其相应活性的影响不一致性,说明在检测miRNA表达水平的同时检测miRNA活性能更全面揭示miRNA的调节功能,为进一步研究let-7家族的调控机制奠定了基础。     

A sensitive and specific HPLC-MS/MS analysis and preliminary pharmacokinetic characterization of isoforskolin in beagle dogs

A sensitive and specific high performance liquid chromatography-electrospray ionization-tandem mass spectrometry (HPLC-ESI-MS/MS) method has been developed and validated for the determination of isoforskolin in canine plasma. Liquid-liquid extraction was used to extract isoforskolin and the internal standard (I.S.) eplerenone from canine plasma. The chromatographic separation was performed on an Agela Venusil XBP Phenyl column with an isocratic mobile phase consisting of methanol-2mM ammonium acetate-formic acid (62:38:0.1, v/v/v), pumped at 0.35 mL/min. Isoforskolin and I.S. were detected at m/z 433.4→373.3 and m/z 415.3→163.5 in positive ion and multiple reaction monitoring (MRM) mode, respectively. The standard curves were linear over the concentration range of 0.1-200 ng/mL (r>0.99). The intra- and inter-batch accuracy values for isoforskolin at four concentrations were 90.2-108.3% and 97.8-106.6%, respectively. The RSDs were less than 6.0%. The mean extraction recoveries of isoforskolin and I.S. were 97.0 and 88.4%, respectively. The method was successfully applied to the pharmacokinetic study after an intravenous administration of isoforskolin in beagle dogs.     

Heterologous extracellular expression and initial characterization of the peroxisomal catalase from the methylotrophic yeast Hansenula polymorpha in Pichia pastoris

Catalase is well known to eliminate H₂O₂ in cells and reduces the toxicity of peroxide compounds. A catalase gene HpCAT1 of methylotrophic yeast Hansenula polymorpha without the part coding the native signal peptide was cloned into expression vector pYM3165 and then integrated into genome of Pichia pastoris GS115 by electroporation. The result of the enzyme activity assay and SDS-PAGE demonstrated that the recombinant protein (HpCAT1) of H. polymorpha was extracellularly expressed in P. pastoris. The expressed catalase was recovered from the culture supernatant of P. pastoris GS115 and purified by (NH₄)₂SO₄ fractionation and Ni-NTA affinity chromatography. The main biochemical properties of the recombinant protein HpCAT1, such as thermodependence and thermostability, pH optimum and pH stability, as well as the effect of metal ions and chemicals, were characterized. With H₂O₂ as the substrate, HpCAT1 displayed pH and temperature optima of ～2.6 and 45°C, respectively. The recombinant HpCAT1 activity was inhibited by 1 mM Hg²⁺ and Cu²⁺, but was highly enhanced by 1.0 mM Fe²⁺.