Structure determination and biochemical studies on Bacillus stearothermophilus E53Q serine hydroxymethyltransferase and its complexes provide insights on function and enzyme memory

Serine hydroxymethyltransferase (SHMT) belongs to the alpha-family of pyridoxal 5'-phosphate-dependent enzymes and catalyzes the reversible conversion of L-Ser and etrahydrofolate to Gly and 5,10-methylene tetrahydrofolate. 5,10-Methylene tetrahydrofolate serves as a source of one-carbon fragment in many biological processes. SHMT also catalyzes the tetrahydrofolate-independent conversion of L-allo-Thr to Gly and acetaldehyde. The crystal structure of Bacillus stearothermophilus SHMT (bsSHMT) suggested that E53 interacts with the substrate, L-Ser and etrahydrofolate. To elucidate the role of E53, it was mutated to Q and structural and biochemical studies were carried out with the mutant enzyme. The internal aldimine structure of E53QbsSHMT was similar to that of the except for significant changes at Q53, Y60 and Y61. The wild-type enzyme, carboxyl of Gly and side chain of L-Ser were in two conformations in the respective external aldimine structures. The mutant enzyme was completely inactive for tetrahydrofolate-depen dent cleavage of L-Ser, whereas there was a 1.5-fold increase in the rate of tetrahydrofolate-independent reaction with L-allo-Thr. The results obtained from these studies suggest that E53 plays an essential role in tetrahydrofolate/5-formyl tetrahydrofolate binding and in the proper positioning of C beta of L-Ser for direct attack by N5 of tetrahydrofolate. Most interestingly, the structure of the complex obtained by cocrystallization of E53QbsSHMT with Gly and 5-formyl tetrahydrofolate revealed the gem-diamine form of pyridoxal 5'-phosphate bound to Gly and active site Lys. However, density for 5-formyl tetrahydrofolate was not observed. Gly carboxylate was in a single conformation, whereas pyridoxal 5'-phosphate had two distinct conformations. The differences between the structures of this complex and Gly external aldimine suggest that the changes induced by initial binding of 5-formyl tetrahydrofolate are retained even though 5-formyl tetrahydrofolate is absent in the final structure. Spectral studies carried out with this mutant enzyme also suggest that 5-formyl tetrahydrofolate binds to the E53QbsSHMT-Gly complex forming a quinonoid intermediate and falls off within 4 h of dialysis, leaving behind the mutant enzyme in the gemdiamine form. This is the first report to provide direct evidence for enzyme memory based on the crystal structure of enzyme complexes.

Effect of Nature of the Precursor on Crystallinity and Microstructure of MOCVD-Grown ZrO2 Thin Films

In the present work, we report the deposition of zirconia thin films on Si(100) at various substrate temperatures by low-pressure metalorganic chemical vapor deposition (MOCVD). Three different zirconium complexes, viz., tetrakis(2,4-pentadionato)zirconium(IV), [Zr(pd)4], tetrakis(2,2,6,6-tetramethyl-3,5-heptadionato)zirconium(IV), [Zr(thd)4], and tetrakis(t-butyl-3-oxo-butanoato)zirconium(IV), [Zr(tbob)4] are used as precursors. The relationship between the molecular structures of the precursors and their thermal properties, as examined by TG/DTA is presented. The films deposited using these precursors have distinctly different morphology, though all of them are of the cubic phase. The films grown from Zr(thd)4 are well crystallized, showing faceted growth at 575°C, whereas the films grown from Zr(pd)4 and Zr(tbob)4 are not well crystallized, and display cracks. These differences in the observed microstructure may be attributed to the different chemical decomposition pathways of the precursors during the film growth, which influence the nucleation and the growth processes. This is also evidenced by the different kinetics of growth from these three precursors under otherwise identical CVD conditions. The details of thin film deposition, and film microstructure analysis by XRD and SEM is presented. The dielectric behavior of the films deposited from different precursors, as studied by C-V measurements, are compared.

Effect of Post-Metallization Hydrogen Annealing on C-V Characteristic of Zirconia Grown Using Atomic Layer Deposition

Substantial amount of fixed charge present in most of the alternative gate dielectrics gives rise to large shifts in the flat-band voltage (VFB) and charge trapping and de-trapping causes hysterectic changes on voltage cycling. Both phenomena affect stable and reliable transistor operation. In this paper we have studied for the first time the effect of post-metallization hydrogen annealing on the C-V curve of MOS capacitors employing zirconia, one of the most promising gate dielectric. Samples were annealed in hydrogen ambient for up to 30 minutes at different temperatures ranging from room temperature to 400°C. C-V measurements were done after annealing at each temperature and the hysteresis width was calculated from the C-V curves. A minimum hysteresis width of ∼35 mV was observed on annealing the sample at 200°C confirming the excellent suitability of this dielectric

Synthesis and DNA binding studies of Ni(II), Co(II), Cu(II) and Zn(II) metal complexes of N(1),N(5)-bis[pyridine-2-methylene]-thiocarbohydrazone Schiff-base ligand

The thiocarbohydrazone Schiff-base ligand with a nitrogen and sulphur donor was synthesized through condensation of pyridine-2-carbaldehyde and thiocarbohydrazide. Schiff-base ligands have the ability to conjugate with metal salts. A series of metal complexes with a general formula [MCl(2)(H(2)L)]center dot nH(2)O (M=Ni, Co, Cu and Zn) were synthesized by forming complexes of the N(1),N5-bis[pyridine-2-methylene]thiocarbohydrazone (H2L) Schiff-base ligand. These metal complexes and ligand were characterized by using ultraviolet-visible (UV-Vis), Fourier Transform Infrared (FT-IR), (1)H and (13)C NMR spectroscopy and mass spectroscopy, physicochemical characterization, CHNS and conductivity. The biological activity of the synthesized ligand was investigated by using Escherichia coli DNA as target. The DNA interaction of the synthesized ligand and complexes on E. coli plasmid DNA was investigated in the aqueous medium by UV-Vis spectroscopy and the binding constant (K(b)) was calculated. The DNA binding studies showed that the metal complexes had an improved interaction due to trans-geometrical isomers of the complexes than ligand isomers in cis-positions. (C) 2011 Elsevier B.V. All rights reserved.

Efficient Algorithms for Computing All Low s-t Edge Connectivities and Related Problems

Given an undirected unweighted graph G = (V, E) and an integer k ≥ 1, we consider the problem of computing the edge connectivities of all those (s, t) vertex pairs, whose edge connectivity is at most k. We present an algorithm with expected running time Õ(m + nk3) for this problem, where |V| = n and |E| = m. Our output is a weighted tree T whose nodes are the sets V1, V2,..., V l of a partition of V, with the property that the edge connectivity in G between any two vertices s ε Vi and t ε Vj, for i ≠ j, is equal to the weight of the lightest edge on the path between Vi and Vj in T. Also, two vertices s and t belong to the same Vi for any i if and only if they have an edge connectivity greater than k. Currently, the best algorithm for this problem needs to compute all-pairs min-cuts in an O(nk) edge graph; this takes Õ(m + n5/2kmin{k1/2, n1/6}) time. Our algorithm is much faster for small values of k; in fact, it is faster whenever k is o(n5/6). Our algorithm yields the useful corollary that in Õ(m + nc3) time, where c is the size of the global min-cut, we can compute the edge connectivities of all those pairs of vertices whose edge connectivity is at most αc for some constant α. We also present an Õ(m + n) Monte Carlo algorithm for the approximate version of this problem. This algorithm is applicable to weighted graphs as well. Our algorithm, with some modifications, also solves another problem called the minimum T-cut problem. Given T ⊆ V of even cardinality, we present an Õ(m + nk3) algorithm to compute a minimum cut that splits T into two odd cardinality components, where k is the size of this cut.

Growth mechanism of the interdiffusion zone between platinum modified bond coats and single crystal superalloys

Pt-modified beta-NiAl bond coats are applied over the superalloys for oxidation protection in jet engine applications. However, as shown in this study, it also enhances the growth of the interdiffusion zone developed between the bond coat and the superalloy along with brittle precipitates. Location of the Kirkendall plane indicates that a precipitate free sublayer grows from the bond coat, whereas another sublayer grows from the superalloy containing very high volume fraction of precipitates. With increasing Pt content, thickness of both the sublayers increases because of an increase in diffusion rates of the components. Quantitative electron probe microanalysis indicates high concentration of refractory components in the precipitates. Transmission electron microscopy shows that Rene N5 superalloy produces TCP phases mu and P, whereas CMSX-4 superalloy produces mu and sigma in the interdiffusion zone. With increasing Pt content in the bond coat, the average size of the precipitates decreases when coupled with Rene N5. Precipitates become much finer when the same bond coats are coupled with CMSX-4. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Growth mechanism of the interdiffusion zone between platinum modified bond coats and single crystal superalloys

Pt-modified beta-NiAl bond coats are applied over the superalloys for oxidation protection in jet engine applications. However, as shown in this study, it also enhances the growth of the interdiffusion zone developed between the bond coat and the superalloy along with brittle precipitates. Location of the Kirkendall plane indicates that a precipitate free sublayer grows from the bond coat, whereas another sublayer grows from the superalloy containing very high volume fraction of precipitates. With increasing Pt content, thickness of both the sublayers increases because of an increase in diffusion rates of the components. Quantitative electron probe microanalysis indicates high concentration of refractory components in the precipitates. Transmission electron microscopy shows that Rene N5 superalloy produces TCP phases mu and P, whereas CMSX-4 superalloy produces mu and sigma in the interdiffusion zone. With increasing Pt content in the bond coat, the average size of the precipitates decreases when coupled with Rene N5. Precipitates become much finer when the same bond coats are coupled with CMSX-4. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Impact of Nigerian Agricultural Cooperative and Rural Development Bank (NACRDB) loan to artisanal fishermen in Lake Kainji

This study was conducted to assess the impact of Nigerian Agricultural, Co-operative and Rural Development Bank Loan on beneficiaries and non-beneficiaries fishermen in Lake Kainji. A total of fifty fishermen (25 beneficiaries and 25 non-beneficiaries) were randomly selected from five fishing villages along the lake basin. Data collected were scored and the percentages of the parameters were calculated appropriately. The types of loans disbursed to beneficiaries revealed that 52% was cash and 48% was in kind. The credit package ranged between N5, 000 to N150, 000 only. Only 48% of the loans granted were paid while the rest remained unpaid. The results obtained from the membership of fishermen Cooperative showed that 64% of beneficiaries were members while 36% were non-members. Also 36% of non-beneficiaries were members while 64% were not. The Common fishing gears used by the two categories of fishermen include gillnets longline, castnet and driftnets. Sixty percent of beneficiaries and 8% of non-beneficiaries fishermen were using canoe with outboard engines while the rest used canoes with paddles. Beneficiaries earned a higher income (N1, 000 to N9, 000) daily than non-beneficiaries (N1, 000 to N6, 000) daily from sales of fish caught. Major contrainsts to increased catch and income identified include inadequate capital, non- availability of fishing inputs, stealing of fishing gears, lack of access to credit facilities and menace of stump and water hyacinth in the lake. Lastly, recommendation were made for the bank management, government and other lending institutions on how to improve the livelihood of the Artisanal fishermen by increasing the loan usually granted

Investment opportunity in improved fish smoker (IFS) as food security for artisanal women fish processors (AWOFPS) in Nigeria: a case study of Kainji Lake area

The Improved Fish Smoker (IFS) was designed and constructed by NIFFR in collaboration with GTZ in 1997. After the on-station trials, five fishing villages with pronounced fishing activities were selected for the demonstration. The IFS and the traditional Smoking Kiln were compared in one of the fishing villages using Gross Margin analysis (GM) and productivity index to determine the profitability and productivity of the two kilns. It was found that the average income of IFS users at fully capacity was N5, 555.50 per day in a year N1.3 million would be realized. Conversely, the average income of the users of Traditional Smoking Kiln (TSK) was N649.00 per day and about N152, 150.50 would be realized in a year. From this estimate, it is evident that the IFS are more profitable than the TSK. Productivity index of the two kilns also revealed that the productivity of IFS is higher than the TSK. Thus, using the IFS would enhance the income of artisanal women Fish Processors (AWOFPS) and ensure food security for the household

I. Studies on bacteriophage DNA's and minicircular DNA's in M. lysodeikticus and E. coli 15. II. Flow dichroism of DNA solutions

Part I

Chapter 1.....A physicochemical study of the DNA molecules from the three bacteriophages, N1, N5, and N6, which infect the bacterium, M. lysodeikticus, has been made. The molecular weights, as measured by both electron microscopy and sedimentation velocity, are 23 x 10⁶ for N5 DNA and 31 x 10⁶ for N1 and N6 DNA's. All three DNA's are capable of thermally reversible cyclization. N1 and N6 DNA's have identical or very similar base sequences as judged by membrane filter hybridization and by electron microscope heteroduplex studies. They have identical or similar cohesive ends. These results are in accord with the close biological relation between N1 and N6 phages. N5 DNA is not closely related to N1 or N6 DNA. The denaturation T_m of all three DNA's is the same and corresponds to a (GC) content of 70%. However, the buoyant densities in CsCl of Nl and N6 DNA's are lower than expected, corresponding to predicted GC contents of 64 and 67%. The buoyant densities in Cs₂SO₄ are also somewhat anomalous. The buoyant density anomalies are probably due to the presence of odd bases. However, direct base composition analysis of N1 DNA by anion exchange chromatography confirms a GC content of 70%, and, in the elution system used, no peaks due to odd bases are present.

Chapter 2.....A covalently closed circular DNA form has been observed as an intracellular form during both productive and abortive infection processes in M. lysodeikticus. This species has been isolated by the method of CsC1-ethidium bromide centrifugation and examined with an electron microscope.

Chapter 3.....A minute circular DNA has been discovered as a homogeneous population in M. lysodeikticus. Its length and molecular weight as determined by electron microscopy are 0.445 μ and 0.88 x 10⁶ daltons respectively. There is about one minicircle per bacterium.

Chapter 4.....Several strains of E. coli 15 harbor a prophage. Viral growth can be induced by exposing the host to mitomycin C or to uv irradiation. The coliphage 15 particles from E. coli 15 and E, coli 15 T^- appear as normal phage with head and tail structure; the particles from E. coli 15 TAU are tailless. The complete particles exert a colicinogenic activity on E.coli 15 and 15 T^-, the tailless particles do not. No host for a productive viral infection has been found and the phage may be defective. The properties of the DNA of the virus have been studied, mainly by electron microscopy. After induction but before lysis, a closed circular DNA with a contour length of about 11.9 μ is found in the bacterium; the mature phage DNA is a linear duplex and 7.5% longer than the intracellular circular form. This suggests the hypothesis that the mature phage DNA is terminally repetitious and circularly permuted. The hypothesis was confirmed by observing that denaturation and renaturation of the mature phage DNA produce circular duplexes with two single-stranded branches corresponding to the terminal repetition. The contour length of the mature phage DNA was measured relative to φX RFII DNA and λ DNA; the calculated molecular weight is 27 x 10⁶. The length of the single-stranded terminal repetition was compared to the length of φX 174 DNA under conditions where single-stranded DNA is seen in an extended form in electron micrographs. The length of the terminal repetition is found to be 7.4% of the length of the nonrepetitious part of the coliphage 15 DNA. The number of base pairs in the terminal repetition is variable in different molecules, with a fractional standard deviation of 0.18 of the average number in the terminal repetition. A new phenomenon termed "branch migration" has been discovered in renatured circular molecules; it results in forked branches, with two emerging single strands, at the position of the terminal repetition. The distribution of branch separations between the two terminal repetitions in the population of renatured circular molecules was studied. The observed distribution suggests that there is an excluded volume effect in the renaturation of a population of circularly permuted molecules such that strands with close beginning points preferentially renature with each other. This selective renaturation and the phenomenon of branch migration both affect the distribution of branch separations; the observed distribution does not contradict the hypothesis of a random distribution of beginning points around the chromosome.

Chapter 5....Some physicochemical studies on the minicircular DNA species in E. coli 15 (0.670 μ, 1.47 x 10⁶ daltons) have been made. Electron microscopic observations showed multimeric forms of the minicircle which amount to 5% of total DNA species and also showed presumably replicating forms of the minicircle. A renaturation kinetic study showed that the minicircle is a unique DNA species in its size and base sequence. A study on the minicircle replication has been made under condition in which host DNA synthesis is synchronized. Despite experimental uncertainties involved, it seems that the minicircle replication is random and the number of the minicircles increases continuously throughout a generation of the host, regardless of host DNA synchronization.

Part II

The flow dichroism of dilute DNA solutions (A₂₆₀≈0.1) has been studied in a Couette-type apparatus with the outer cylinder rotating and with the light path parallel to the cylinder axis. Shear gradients in the range of 5-160 sec.^-1 were studied. The DNA samples were whole, "half," and "quarter" molecules of T4 bacteriophage DNA, and linear and circular λb₂b₅c DNA. For the linear molecules, the fractional flow dichroism is a linear function of molecular weight. The dichroism for linear A DNA is about 1.8 that of the circular molecule. For a given DNA, the dichroism is an approximately linear function of shear gradient, but with a slight upward curvature at low values of G, and some trend toward saturation at larger values of G. The fractional dichroism increases as the supporting electrolyte concentration decreases.

Altered expression of Alzheimer's disease-related genes in the cerebellum of autistic patients: a model for disrupted brain connectome and therapy

Autism and Alzheimer's disease (AD) are, respectively, neurodevelopmental and degenerative diseases with an increasing epidemiological burden. The AD-associated amyloid-beta precursor protein-alpha has been shown to be elevated in severe autism, leading to the 'anabolic hypothesis' of its etiology. Here we performed a focused microarray analysis of genes belonging to NOTCH and WNT signaling cascades, as well as genes related to AD and apoptosis pathways in cerebellar samples from autistic individuals, to provide further evidence for pathological relevance of these cascades for autism. By using the limma package from R and false discovery rate, we demonstrated that 31% (116 out of 374) of the genes belonging to these pathways displayed significant changes in expression (corrected P-values <0.05), with mitochondria- related genes being the most downregulated. We also found upregulation of GRIN1, the channel-forming subunit of NMDA glutamate receptors, and MAP3K1, known activator of the JNK and ERK pathways with anti-apoptotic effect. Expression of PSEN2 (presinilin 2) and APBB1 (or F65) were significantly lower when compared with control samples. Based on these results, we propose a model of NMDA glutamate receptor-mediated ERK activation of alpha-secretase activity and mitochondrial adaptation to apoptosis that may explain the early brain overgrowth and disruption of synaptic plasticity and connectome in autism. Finally, systems pharmacology analyses of the model that integrates all these genes together (NOWADA) highlighted magnesium (Mg2+) and rapamycin as most efficient drugs to target this network model in silico. Their potential therapeutic application, in the context of autism, is therefore discussed.

火烧、施肥、刈割及其交互作用对草原土壤净氮矿化的影响

我国北方温带草原地处干旱半干旱区，是欧亚大陆草原生物区系的重要组成部分，也是我国重要的畜牧业生产基地。土壤氮素作为陆地植物生长和生态系统初级生产力的主要限制因子之一，了解其矿化和可利用性对各种人为干扰因素的响应，有助于我们充分认识草地退化机理，维持草场生产力并进一步促进畜牧业的可持续发展，为草地恢复、重建和维护提供理论依据。本实验在中国科学院内蒙古草原生态系统定位研究站的多年围封退化样地，分别实施了火烧、施肥、刈割及其交互作用的人为干扰处理，利用原状土野外培养的方法，在两年时间中，研究不同的人为干扰因素（火烧、施肥、刈割及其交互处理）对土壤净氮矿化作用的影响。 火烧显著影响草原的氮循环过程，季节和年际的气候变化参与调节氮循环对火烧处理的响应。多年围封后的初次人工火烧处理显著降低了第一个生长季（2006 年生长季）和其后冬季的土壤净氮矿化速率，但是，火烧处理仅在冬季对土壤无机氮含量产生显著降低作用；2007 年生长季，火烧处理对土壤净氮矿化速率和土壤无机氮含量没有显著作用，但是在个别月份，不同的火烧频率对土壤净氮矿化速率和无机氮含量的影响表现出差异。2006 年生长季，未火烧样地和火烧样地净氮矿化积累量分别为3.07±0.26 g N m-2 和2.18±0.21 g N m-2；冬季，未火烧样地和火烧样地净氮矿化积累量分别为1.18±0.25 g N m-2 和0.51±0.08 g N m-2；2007 年生长季，未火烧样地（BC）、每年火烧样地（B1）和两年一烧样地（B2）净氮矿化积累量分别为1.32±0.21 g N m-2、0.54±0.30 g N m-2 和 0.77±0.24 g N m-2。较为湿润的2006 年生长季的净氮矿化积累量显著高于较为干旱的2007 年生长季，冬季也存在相当丰富的净氮矿化积累量。我们推论，长时间围封后的单次火烧处理对土壤净氮矿化作用的影响可能是短效的，但是年际间气候变化对土壤净氮矿化作用影响显著。 施肥显著提高了土壤的无机氮含量，并且与施肥梯度呈显著正相关关系。施肥对土壤无机氮含量的影响具有累加效应，第一次施肥和第二次施肥后的首次取样，+N5.25 、+N17.5 、+N28.0 三个施肥梯度的样地土壤无机氮含量比未施肥样地分别高出56%、219%、1054%和514%、891%、1811%。施肥处理在2006 年和2007 年对土壤净氮矿化作用都没有显著影响，仅在2007 年的个别月份有一定效果。以上结果说明，无机氮肥的添加可以明显提高土壤中无机氮的含量，满足植物生长的需求，但对于土壤氮转化过程的影响可能还要受其它环境和生物因子的制约。 刈割对土壤无机氮含量和净硝化速率没有显著作用，对土壤净氮矿化速率仅在个别月份表现显著效果。2007 年生长季，未刈割样地和刈割样地净氮矿化积累量分别为1.32±0.21 g N m-2 和1.08±0.35 g N m-2，不存在显著差异。我们推论，长期围封后的单次刈割处理在短期内对生长季的土壤氮动态仅有微弱影响，并且这种效果还可能受水分因素的制约。 火烧、施肥、刈割的交互处理在2007 年生长季对土壤无机氮含量产生显著作用，但是，对土壤净氮矿化速率和净硝化速率没有显著效果，然而，在不同的取样时间，火烧、施肥、刈割的交互处理对土壤无机氮含量、净氮矿化速率和净硝化速率的影响存在显著差异，说明火烧、施肥、刈割的交互处理对土壤无机氮和净氮矿化作用的影响可能受各种环境因子的制约，尤其是在水分相对缺乏的半干旱内蒙古草原，非生物因子和生物因子可能共同影响着土壤中的氮平衡。 本研究初步分析了长期围封后火烧、施肥、刈割及其交互处理对土壤净氮矿化的影响，初步探究了人为干扰和环境气候变化对土壤可利用性氮的调节作用，为科学地进行禁牧、割草、人工养份添加等草原管理提供了数据支持。

印度人群线粒体 DNA 系统发育基因组学研究

人类线粒体DNA(mtDNA)是一个长度16,569bp 的环状分子，编码13 种蛋白 质、22 种tRNA 和2 种rRNA。由于mtDNA 全基因组信息具有缺乏重组、母系 遗传、高突变速率和相对较高的分辨率等特点，近年来已经成为重建人类历史的 重要工具。这些研究已经证实，mtDNA 最古老的六个单倍型类群，L0-L5，在非 洲特异的出现；而6-7 万年前从L3 衍生出的M 和N 两个超类群最终占领了世界 其他地区。然而，mtDNA 全序列研究在世界上某些特定地区尚是一片空白，其 中之一便是作为人类“走出非洲”的关键区域——印度。 为弥补这一空白，我们从 1200 个印度样品中选择了131 个可以代表所有主 要单倍型类群的个体，进行了全基因组扩增和测序，手工重建并软件验证了系统 发育关系树。我们的结果发现了12 个新的印度特有单倍型类群(N5, R7, R8, R30, R31, M34-M40)，修订了11 个已知特有单倍型类群(N1d, R5, R6, U2a, U2b, U2c, M2, M4, M5, M6, M30)的定义，详细描述了存在于印度的欧洲特有类群(HV, JT, U, N1, W)。 这一工作产生了多个推论。第一个是关于人类“走出非洲”假说长期以来 存在的争论。欧亚大陆和大洋洲mtDNA 在M 和N(包括R)超类群系统发育关系 上星状和不重叠的分布，表明了人类走出非洲是沿着亚洲海岸线(即所谓的“南 方路线”)的一个快速扩散的过程。第二个推论是关于存在于印度的欧洲特有世 系。与典型的欧洲世系相比，这些世系仅仅存在一到两个突变，从而证实了新石 器时代以来来自于近东新月地带或中亚高原的基因流。第三个推论涉及一个早期 的印度全序列研究。仔细分析其数据表明，他们的数据丢失了很多基部的特有突 变并产生了多个幻影突变，从而证实了系统发育思想对检测数据质量的作用。 随着印度人群 mtDNA 全序列研究的完成，人类mtDNA 系统发育的基本框 架得以建立。人类mtDNA 明显地呈现出大洲特异性分布。目前已经有两种假说用来解释这一现象。传统的观点把这一现象归于遗传漂变；而近期的选择假说认 为选择在人类mtDNA 的分化中扮演了极其重要的角色，而气候是主要的选择压 力。为解决这一争论，我们收集了来自南亚、大洋洲和东亚三个具有不同气候的 地区的mtDNA，使用直接计数的办法比较了各个大洲之间同义突变和异义突变 的差异。结果表明，几乎在所有的基因中，异义突变的数量低于同义突变的数量， 从而表明纯净化选择是人类mtDNA 进化中的主要力量。然而，在这三个大洲之 间没有发现显著的差异，表明mtDNA 在这三个区域上所承受的选择压力基本相 同。这一结果表明，气候不大可能是造成人类mtDNA 分化的主要原因。

全球变化背景下科尔沁沙地生态系统C、N循环过程

工业革命以来，由于人口的快速增加和人类活动的强烈干扰（主要包括煤炭、石油等石化燃料的燃烧、化肥生产和使用）导致土地利用/覆被变化、大气CO2浓度升高、N沉降等一系列全球环境变化问题。有关陆地生态系统生物地球化学循环，尤其是陆地生态系统C、N循环及其耦合过程方面的研究成为全球变化科学研究领域的重要内容。 干旱/半干旱地区占地球陆地总面积的1/3。与湿润地区相比较，干旱/半干旱地区生态系统稳定性比较差，往往属于生态脆弱区。因此，全球变化对干旱/半干旱地区生态系统影响更加敏感。科尔沁沙地位于我国北方干旱/半干旱地区，是我国典型的农牧交错区和生态脆弱区。科尔沁沙地是世界上人口密度最高的干旱/半干旱地区之一，人类活动对其影响剧烈。然而，有关科尔沁沙地生态系统C、N元素生物地球化学循环过程对土地利用/覆被变化、N沉降等全球变化响应及其反馈机制的研究非常缺乏。因此，本文以科尔沁沙地退化沙质草地、农田、不同年龄樟子松和杨树人工林等生态系统为对象，开展了造林、模拟N沉降和凋落物管理对生态系统C、N元素循环过程影响的研究。 在科尔沁沙地东南缘，以退化沙质草地、樟子松（Pinus sylvestris var. mongolica）人工林（15、24和30年生）、杨树（Poplus xiaozhuanica）人工林（7、11和15年生）为对象，研究草地转变为林地对生态系统C、N储量影响；以退化草地、榆树疏林草地和32年生樟子松人工林为对象，比较草地造林对土壤C、N循环过程及其土壤微生物性状的影响；以农田和5、10、15年生杨树人工林为对象，研究退耕还林对生态系统C、N储量和循环过程影响；以35年生樟子松人工林为对象，模拟研究N沉降和凋落物管理对生态系统C、N循环过程影响。通过上述研究，得到以下主要结果： （1）草地生态系统总C储量为34.38 Mg ha-1，15、24和30年生樟子松人工林生态系统总C储量分别为43.56、60.45和66.59 Mg ha-1，7、11和15年生杨树人工林生态系统总C储量分别为34.54、48.26和78.77 Mg ha-1；与农田相比，退耕5年的杨树人工林生态系统总C库储量下降13%，而10年和15年杨树人工林分别增加了176%和5倍；随着人工林年龄的增加，地上植被生物量C库储量占生态系统总C库储量的比例逐渐增加，并主要分配在树干。草地生态系统总N库储量为2.54 Mg ha-1，15、24和30年生樟子松人工林生态系统总N库储量分别为1.96、2.10和2.19 Mg ha-1，7、11和15年生杨树人工林生态系统总N库储量分别为2.27、1.84和2.60 Mg ha-1；与农田相比，退耕5年的杨树人工林生态系统总N库储量下降32%，而10年和15年杨树人工林分别增加了47%和76%；农田和草地造林后生态系统N储量依然主要分配在土壤中。 （2）草地和农田造林后土壤C、N库储量的变化受多因子的影响，例如林龄、树种种类以及立地条件等。农田和草地造林初期，土壤C、N库储量表现出下降趋势，随着林龄的增加，土壤C、N储量逐渐恢复。草地营造樟子松人工林30年后，0–60 cm深度土壤C、N储量依然显著低于草地；与草地相比，15年生杨树人工林土壤C、N储量差异不显著。在立地条件较好的情况下，10年杨树人工林土壤C、N储量已显著高于农田；然而，在立地条件相对较差的情况下，15年杨树人工林土壤C、N储量仍然与农田相比差异不显著。 （3）土地利用变化能够强烈地改变土壤C、N循环过程。与草地或疏林草地相比，32年生樟子松人工林土壤C、N、P含量显著降低；土壤C、N矿化过程发生显著变化，并且受季节变化的影响；在不同季节，土壤微生物量碳含量、代谢熵（qCO2）、微生物熵（MBC/TOC）以及土壤酶活性等在不同土地利用条件下表现出规律不一致。同样，农田退耕杨树人工林能够显著影响土壤C、N矿化过程，土壤无机氮（铵态氮+硝态氮）含量，土壤微生物量碳含量以及土壤微生物活性。草地造林在一定程度上导致土壤质量下降。而农田造林有利于土壤质量改善，尤其在在立地条件较好情况下。 （4）N添加增加对沙地樟子松人工林地上和地下C、N元素含量影响不大；N添加1年后，仅林下植被C、N含量显著增加，高氮处理（N15）凋落物N含量显著增加。N添加抑制了沙地樟子松人工林凋落物的早期分解和N、P元素释放。5、6、8和9月份土壤无机N含量均随着N输入增加表现出一定程度的增加，然而，7月份N添加导致土壤无机N含量降低。N添加对土壤潜在N矿化速率影响不显著。7和8月份N添加影响土壤C矿化速率，而其它月份影响不显著。低氮处理（N5）有利于增加土壤微生物量碳含量，而高氮处理（N15）在一定程度上降低土壤微生物量碳含量。 （5）凋落物输入变化（凋落物添加和凋落物移出）在一定程度上改变了35年生沙地樟子松人工林生态系统C、N循环过程。凋落物移出（C0）增加了林下植被C含量，降低了树木叶片N含量。凋落物移出抑制了凋落物分解和P元素的释放，而增加了C元素的早期释放速率，对N元素释放过程影响不显著。凋落物输入变化对不同月份土壤无机N含量和土壤N矿化过程影响均不显著。仅在6月份凋落物移出显著抑制了土壤C矿化速率，其它月份差异均不显著。凋落物管理对土壤微生物量碳含量影响不显著。 以上研究结果表明，土地利用变化、N沉降和凋落物输入改变等能够影响半干旱地区沙地生态系统C、N储量和循环过程。尤其是土地利用变化强烈改变沙地生态系统C、N储量、分配格局和循环过程，并且受到多因子的影响。科尔沁沙地樟子松人工林生态系统C、N元素生物地球化学循环存在密切的耦合关系。今后有必要进一步结合3S技术、同位素技术、模型模拟以及分子生物学技术等，从微观-宏观不同尺度上，研究半干旱地区沙地生态系统C、N循环过程对全球变化的响应及其反馈机制。

细胞色素c突变体的共振拉曼光谱研究

采用共振拉曼光谱技术研究了细胞色素 c一次突变体 ( WT)及其二次突变体 Y67F和 N5 2 I在低频区的光谱特征 .结果表明 ,以苯丙氨酸替代 WT中酪氨酸残基 Tyr 67并没有明显影响血红素丙氨酸侧基周围多肽氨基酸残基的构象 ,而异亮氨酸对天冬酰胺残基 Asn5 2的取代则较大程度地改变了蛋白质内部水分子与周围氨基酸残基间的氢键作用和多肽空腔的疏水性 ,进而使氨基酸残基和血红素的构象相应发生调变 .两种取代都导致形成血红素周围空腔的多肽氨基酸残基构象的变化