Photosynthetic bicarbonate utilization inPorphyra haitanensis (Bangiales, Rhodophyta)

The activities of carbonic anhydrase (CA) and photosynthesis of Porphyra haitanensis were investigated in order to see its photosynthetic utilization of inorganic carbon source. Both intra- and extra-cellular CA activities existed in the thallus. CA inhibitors, acetazolamide (AZ) and ethoxyzolamide (EZ), remarkably depressed the photosynthetic oxygen evolution in seawater of pH 8.2 and 10.0, and EZ showed stronger inhibition than AZ. The observed net photosynthetic rate in seawater of pH 8.2 was much higher than that of CO2 supply theoretically derived from spontaneous dehydration of HCO3-. P. haitanensis also showed a rather high pH compensation point (9.9). The results demonstrated that P. haitanensis could utilize bicarbonate as the external inorganic carbon source for photosynthesis. The bicarbonate utilization was closely associated with dehydration catalyzed by extracellular CA activity. The inorganic carbon composition in seawater could well saturate the photosynthesis of P. haitanensis. The low Km value and compensation points for inorganic carbon reflected the existence of CO2- concentrating mechanism in this alga.     

Atmospheric carbon dioxide concentrations over the past 60 million years

Knowledge of the evolution of atmospheric carbon dioxide concentrations throughout the Earth's history is important for a reconstruction of the links between climate and radiative forcing of the Earth's surface temperatures. Although atmospheric carbon dioxide concentrations in the early Cenozoic era (about 60 Myr ago) are widely believed to have been higher than at present, there is disagreement regarding the exact carbon dioxide levels, the timing of the decline and the mechanisms that are most important for the control of CO2 concentrations over geological timescales. Here we use the boron-isotope ratios of ancient planktonic foraminifer shells to estimate the pH of surface-layer sea water throughout the past 60 million years, which can be used to reconstruct atmospheric CO2 concentrations. We estimate CO2 concentrations of more than 2,000 p.p.m. for the late Palaeocene and earliest Eocene periods (from about 60 to 52 Myr ago), and find an erratic decline between 55 and 40 Myr ago that may have been caused by reduced CO2 outgassing from ocean ridges, volcanoes and metamorphic belts and increased carbon burial. Since the early Miocene (about 24 Myr ago), atmospheric CO2 concentrations appear to have remained below 500 p.p.m. and were more stable than before, although transient intervals of CO2 reduction may have occurred during periods of rapid cooling approximately 15 and 3 Myr ago.     

Exogenous carbon acquisition of photosynthesis in Porphyra haitanensis (Bangiales, Rhodophyta) under emersed state

The photosynthetic performances of Porphyra haitanensis thalli were investigated in order to understand its mechanisms for exogenous carbon acquisition during emersion at low tide. The emersed photosynthesis was studied by altering the pH value in the water film on the thalli surface, treating them with carbonic anhydarase inhibitors (acetazolamide and 6-ethoxyzolamide), adjusting the CO2 concentrations in the air, and comparing the theoretical maximum CO2 supply rates within the adherent water film with the observed photosynthetic CO2 uptake rates. It was found that the principal exogenous inorganic carbon source for the photosynthesis of P. haitanensis during emersion was atmospheric CO2. The driving force of CO2 flux across the water film was the CO2 concentration gradient within it. Carbonic anhydrase accelerated both extracellular and intracellular CO2 transport. The emersed photosynthesis of P. haitanensis was limited by the present atmospheric CO2 level, and would be enhanced by atmospheric CO2 rise that would trigger global warming.     

An inducible CO2 concentrating mechanism in cyanobacteriumAnabaena sp. strain PCC7120

In order to define its characteristics of the photosynthetic utilization of CO2 and HCO3-when the ambient inorganic carbon changed, HCG (High-CO2-Growing Cells) of cyanobacteri-um Anabaena sp. strain PCC7120 were prepared. The growth rate of HCG was higher than that of LCG (low-CO2-growing cells, i.e. air-growing cells). When the HCG cells were transferred from 5% CO2 to air levels of CO2 ,a series of changes took place: its carbonic anhydrase activity as well as its photosynthetic affinity to the external inorganic carbon significantly increased; the number of the carboxysomes, which is one of the most important components of CCM in cyanobacteria also increased. These facts indicated that the CCM activity of Anabaena PCC 7120 was induced. When the pH in the medium increased from 6 to 9, the photosynthetic affinity to external inorganic carbon of both HCG and LCG declined, while the apparent photo-synthetic affinity to external CO2 increased. In the light of these findings, this inducible CCM in cyanobacteria provided a good model for the study of the photosynthetic Ci utilization in the pho-totrophic microoganisms.     

高浓度CO_2对小新月菱形藻胞外碳酸酐酶活性和光合作用的影响

以赤潮硅藻小新月菱形藻(Nitzschia closterium var.minutissima)为实验材料,研究了短期内(12 h)高浓度CO2(5%CO2)对其胞外碳酸酐酶活性和光合作用的影响,结果显示,高浓度CO2培养导致小新月菱形藻胞外碳酸酐酶活性、叶绿素a和叶绿素c含量明显下降.与通空气培养(0.035%CO2)相比,在短期内(12 h)胞外碳酸酐酶活性下降了75.4%,叶绿素a、c含量分别降低了5.6%和7.3%;高浓度CO2培养下最大光化学效率(Fv/Fm)、实际光化学效率(Yield)和光化学淬灭系数(qP)下降,但非光化学淬灭系数(gN)升高.研究结果表明,高浓度CO2对胞外碳酸酐酶活性具有明显的抑制作用,小新月菱形藻通过调整光系统Ⅱ的能量流动和能量利用效率以适应高浓度CO2的环境.     

Structure and metal exchange in the cadmium carbonic anhydrase of marine diatoms

Carbonic anhydrase, a zinc enzyme found in organisms from all kingdoms, catalyses the reversible hydration of carbon dioxide and is used for inorganic carbon acquisition by phytoplankton. In the oceans, where zinc is nearly depleted, diatoms use cadmium as a catalytic metal atom in cadmium carbonic anhydrase (CDCA). Here we report the crystal structures of CDCA in four distinct forms: cadmium-bound, zinc-bound, metal-free and acetate-bound. Despite lack of sequence homology, CDCA is a structural mimic of a functional beta-carbonic anhydrase dimer, with striking similarity in the spatial organization of the active site residues. CDCA readily exchanges cadmium and zinc at its active site--an apparently unique adaptation to oceanic life that is explained by a stable opening of the metal coordinating site in the absence of metal. Given the central role of diatoms in exporting carbon to the deep sea, their use of cadmium in an enzyme critical for carbon acquisition establishes a remarkable link between the global cycles of cadmium and carbon.     

海洋浮游藻(Emiliania huxleyi)无机碳利用机理

探讨了海洋浮游藻Emilianiahuxleyi无机碳利用机制以及与藻龄间的关系．结果表明Emilianiahuxleyi细胞在其指数（生长）期和静止（生长）期对无机碳利用的途径不同．指数期细胞是通过HCO-3直接吸收途径,同时还与钙化作用有关,而静止期细胞则是通过CO2吸收途径,存在细胞外碳酸酐酶．     

Unicellular C4 photosynthesis in a marine diatom

Nearly 50 years ago, inorganic carbon was shown to be fixed in microalgae as the C3 compound phosphoglyceric acid. The enzyme responsible for C3 carbon fixation, ribulose-1,5-bisphosphate carboxylase (Rubisco), however, requires inorganic carbon in the form of CO2 (ref. 2), and Rubisco enzymes from diatoms have half-saturation constants for CO2 of 30-60 microM (ref. 3). As a result, diatoms growing in seawater that contains about 10 microM CO2 may be CO2 limited. Kinetic and growth studies have shown that diatoms can avoid CO2 limitation, but the biochemistry of the underlying mechanisms remains unknown. Here we present evidence that C4 photosynthesis supports carbon assimilation in the marine diatom Thalassiosira weissflogii, thus providing a biochemical explanation for CO2-insensitive photosynthesis in marine diatoms. If C4 photosynthesis is common among marine diatoms, it may account for a significant portion of carbon fixation and export in the ocean, and would explain the greater enrichment of 13C in diatoms compared with other classes of phytoplankton. Unicellular C4 carbon assimilation may have predated the appearance of multicellular C4 plants.     

Structural basis for glycosphingolipid transfer specificity

Lipid transfer proteins are important in membrane vesicle biogenesis and trafficking, signal transduction and immunological presentation processes. The conserved and ubiquitous mammalian glycolipid transfer proteins (GLTPs) serve as potential regulators of cell processes mediated by glycosphingolipids, ranging from differentiation and proliferation to invasive adhesion, neurodegeneration and apoptosis. Here we report crystal structures of apo-GLTP (1.65 A resolution) and lactosylceramide-bound (1.95 A) GLTP, in which the bound glycosphingolipid is sandwiched, after adaptive recognition, within a previously unknown two-layer all-alpha-helical topology. Glycosphingolipid binding specificity is achieved through recognition and anchoring of the sugar-amide headgroup to the GLTP recognition centre by hydrogen bond networks and hydrophobic contacts, and encapsulation of both lipid chains, in a precisely oriented manner within a 'moulded-to-fit' hydrophobic tunnel. A cleft-like conformational gating mechanism, involving two interhelical loops and one alpha-helix of GLTP, could enable the glycolipid chains to enter and leave the tunnel in the membrane-associated state. Mutation and functional analyses of residues in the glycolipid recognition centre and within the hydrophobic tunnel support a framework for understanding how GLTPs acquire and release glycosphingolipids during lipid intermembrane transfer and presentation processes.     

基于随机森林的公路隧道CO气体浓度预测模型

汽车尾气的主要成分是CO气体，是公路隧道通风设计的一项重要参数。准确、快速地预测隧道内CO气体浓度，能够为隧道通风控制提供有力参考，有助于CO气体浓度的及时控制，对保障隧道内人员的健康、安全和隧道绿色节能十分必要。采用公路隧道实地监测CO气体浓度数据，建立了以监测点位置、交通量、车速、风速为输入特征的公路隧道CO气体浓度预测随机森林模型。通过整理3 300 m长隧道CO气体浓度数据，对比了CO气体浓度实测数据与模型预测值，验证了模型的预测精度。结果表明，基于随机森林建立的CO气体浓度预测模型具有良好的预测精度，能够准确地预测隧道内CO气体浓度，测试集的均方根误差(root mean square error, RMSE )和决定系数(R2)分别为0.4974和0.9437；该预测模型性能显著优于线性回归模型和支持向量机模型；预测模型能够推广应用于其他隧道的CO气体浓度预测，对应的RMSE和R2分别为0.9095和0.7295，可以在已知测点位置、交通量、车速、风速的情况下预判隧道内CO气体浓度，为隧道通风控制或安全预警提供数据参考；特征重要性分析结果显示，测点位置对隧道内CO浓度的影响最大，在隧道出口处CO气体浓度值最高；随着风速的增大，隧道内CO气体浓度逐渐减小。     

内生枯草芽孢杆菌HD-1β-甘露聚糖酶基因的克隆及结构生物学分析

采用PCR技术从一株内生枯草芽孢杆菌HD-1基因组DNA中扩增出β-甘露聚糖酶基因核苷酸编码序列.序列分析表明,该基因全长1 089bp,编码362个氨基酸和一个终止密码子,N端前27个氨基酸为其信号肽.该酶氨基酸序列与相同来源的β-甘露糖苷酶同源性最高达98.34%,具有ManB保守结构域,属于糖苷水解酶家族26的一员.通过对该酶分子三维结构的预测分析,该酶的催化域形成TIM桶状结构,Cys92和Cys112形成二硫键,它们之间的部分构成该酶的氧化还原反应的活性中心,Glu100和Glu292分别为该酶的酸碱催化位点和亲核催化位点.三维结构的分析为提高酶的催化活性的和功能方面的定向改造提供了依据.     

超临界流体技术在生物工程中的应用

介绍了超临界二氧化碳(SC-CO2)的特点及作为生物反应介质的优点;SC-CO2对脂肪酶、水解酶、氧化酶等多种酶的催化活性的影响较小;对于微生物这一活性个体,在SC-CO2相态中其生理活性将受到显著影响,但对某些特定的微生物(如耐压微生物)的生物反应则具有可行性.简要介绍了SC-CO2流体技术的理论研究进展和应用领域.     

高速公路隧道纵向通风的智能控制

高速公路隧道内的 CO浓度、可见度等环境参数是保证隧道正常运行所需要控制的重要参数 ,通过高速公路隧道通风来保证这些参数在安全的范围内。通风设备是高速公路隧道运营中电能消耗的主要设备 ,是节能的主要对象。高速公路隧道是一个带滞后的大惯性对象 ,存在许多不确定干扰。本文在分析隧道纵向通风特点的基础上 ,提出了一种隧道纵向通风的智能控制方法 ,该智能控制方法基于模式识别和最优控制理论 ,具有较强的鲁棒性和因后期隧道改造而变动的适应能力 ,达到了安全和节能的目的。     

Triple oxygen isotope evidence for elevated CO2 levels after a Neoproterozoic glaciation

Understanding the composition of the atmosphere over geological time is critical to understanding the history of the Earth system, as the atmosphere is closely linked to the lithosphere, hydrosphere and biosphere. Although much of the history of the lithosphere and hydrosphere is contained in rock and mineral records, corresponding information about the atmosphere is scarce and elusive owing to the lack of direct records. Geologists have used sedimentary minerals, fossils and geochemical models to place constraints on the concentrations of carbon dioxide, oxygen or methane in the past. Here we show that the triple oxygen isotope composition of sulphate from ancient evaporites and barites shows variable negative oxygen-17 isotope anomalies over the past 750 million years. We propose that these anomalies track those of atmospheric oxygen and in turn reflect the partial pressure of carbon dioxide (P(CO2)) in the past through a photochemical reaction network linking stratospheric ozone to carbon dioxide and to oxygen. Our results suggest that P(CO2) was much higher in the early Cambrian than in younger eras, agreeing with previous modelling results. We also find that the (17)O isotope anomalies of barites from Marinoan (approximately 635 million years ago) cap carbonates display a distinct negative spike (around -0.70 per thousand), suggesting that by the time barite was precipitating in the immediate aftermath of a Neoproterozoic global glaciation, the P(CO2) was at its highest level in the past 750 million years. Our finding is consistent with the 'snowball Earth' hypothesis and/or a massive methane release after the Marinoan glaciation.     

Copper ions inactivate S-adenosylhomocysteine hydrolase

S-adenosylhomocysteine (AdoHcy) hydrolase isan enzyme that regulates biomethylation and some otherphysiological processes. Recombinant AdoHcy hydrolase wasoverexpressed in E. coli JM109 and purified with ion ex-change and gel filtration chromatographies. The effects ofcopper ions (Cu2+) on the activity of AdoHcy hydrolase wereinvestigated and the results showed that Cu2+ inhibited theenzyme's activity by a concentration and time-dependentprocess. The inhibition constant (Ki) and the apparent rateconstant (kapp) were calculated to be (14 + 4) nmol @ L-1 and(1.08 + 0.15) min-1, respectively. The existence of the naturalsubstrate Ado could to some extent prevent Cu2+ from inac-tivating the enzyme, suggesting that copper ions possiblycould compete with the natural substrate on enzyme's sub-strate binding site. Further studies on the mechanism of in-hibition are being carried out.     

纵向通风隧道正常运营CO浓度限值计算

我国《公路隧道通风照明设计规范》与国外标准对隧道内CO浓度限值的设定在计算方法和取值上都存在差异.针对射流风机式及竖井送排与射流风机组合式纵向通风隧道CO浓度分布特性,基于差分形式的Coburn-Forster-Kane方程(CFK方程),拟合了两类典型纵向通风隧道正常运营CO浓度限值计算式.结果表明:尽管两类隧道具有不同的CO浓度分布特性,工程中可按相同的限值设计;对于长隧道,我国应设定更严格的限值标准.     

绿豆环氧水解酶在硅基介孔材料上的固载及催化性能

从绿豆中提取粗酶并优化,活性测定反应条件,结果表明,在40 ℃、pH=7的条件下,酶反应活性最高。将来源于绿豆的环氧水解酶固载于多种硅基介孔材料上,考察了多种因素对固定化酶活性的影响。研究发现,以大孔径、表面疏水性的材料作为载体,采用共价方法固载酶,可以得到较高的酶固载率,同时固载酶表现出较高的催化反应活性,并且可以循环使用多次。     

Rubisco without the Calvin cycle improves the carbon efficiency of developing green seeds

Efficient storage of carbon in seeds is crucial to plant fitness and to agricultural productivity. Oil is a major reserve material in most seeds, and these oils provide the largest source of renewable reduced carbon chains available from nature. However, the conversion of carbohydrate to oil through glycolysis results in the loss of one-third of the carbon as CO2. Here we show that, in developing embryos of Brassica napus L. (oilseed rape), Rubisco (ribulose 1,5-bisphosphate carboxylase/oxygenase) acts without the Calvin cycle and in a previously undescribed metabolic context to increase the efficiency of carbon use during the formation of oil. In comparison with glycolysis, the metabolic conversion we describe provides 20% more acetyl-CoA for fatty-acid synthesis and results in 40% less loss of carbon as CO2. Our conclusions are based on measurements of mass balance, enzyme activity and stable isotope labelling, as well as an analysis of elementary flux modes.     

嗜碱芽孢杆菌NTT33β-甘露聚糖酶的特性研究

本文研究了嗜碱芽孢杆菌（ Ｂａｃｉｌｌｕｓ ａｌｋａｌｏｐｈｉｌｉｃ） Ｎ Ｔ Ｔ３３β－ 甘露聚糖酶的产生条件和酶学性质．其产酶的最佳碳源为 １％ 槐豆角,最佳氮源为 １％ 蛋白胨＋ ０．２％ 酵母膏,发酵培养３６ｈ 产酶量最高（达 ６１．３ｕ／ｍ ｌ）．甘油、葡萄糖、甘露醇等对产酶有强的阻遏作用．经分离纯化后测得纯酶的分子量为３８．９ Ｋ Ｄ,等电点 ｐ Ｉ为３．０,酶反应最适 ｐ Ｈ 为 ９．０～１０．０,最适温度为８０℃,稳定 ｐ Ｈ 为６．０～９．０,稳定温度为６０℃以下,金属离子中 Ｃｕ２＋ , Ｂａ２＋ , Ｍ ｇ２＋ , Ａｌ３＋ , Ｃｏ２＋ 对该酶有一定的激活作用,而 Ａｇ＋ , Ｈｇ２＋ , Ｍｎ２＋ 对该酶有明显抑制作用     

湖相碳酸盐岩有机质热演化产物及其碳同位素组成特征

通过泌阳凹陷第三系核桃园组核三段湖相碳酸盐岩的热模拟实验,对有机质演化特征、释放气体组分及含碳气体碳同位素组成特征获得了以下认识：（1）释放气体主要以二氧化碳和烷烃类气为主,含有少量烯烃气体,在300～400℃时达到气体释放峰,随温度的升高,C4～C5较重烷烃气含量增加。二氧化碳随温度的升高释放量增大,主要为碳酸盐分解贡献;（2）含碳气体碳同位素随温度的升高增重,在气体释放峰温度段350℃左右时发生明显“转折”,碳同位素组成明显变重,结果造成在不同的热演化阶段碳同位素值有较大范围的变化。