樟子松人工林分枝结构的分析

基于对6块樟子松(Pinus sylvestris var. mongolica)人工林固定标准地中的30株样木枝解析调查数据,通过分析不同林分、不同大小林木1级枝和2级枝的分枝概率、分枝格局和分枝角度,揭示了樟子松人工林树冠的分枝结构特点。研究结果表明：樟子松人工林1级枝和2级枝的平均分枝数量分别为3.84个和2.80个,两者分枝概率均呈正态分布;1级和2级枝条在光照条件好的几个区间（方位角46°～225°）分布较多,1级枝条的水平分布遵从均匀分布,而2级枝条则不遵从均匀分布;树冠上层枝条的分枝角度略小于树冠中、下层,上层平均分枝角度为45.6°,而中下层平均分枝角度都为49.4°。不同大小林木的1级枝分枝结构规律表明：Ⅰ级木和Ⅴ级木的每轮平均分枝数非常接近,分别为3.89和3.94个,比Ⅲ级木每轮分枝数大0.5个左右;1级枝水平分布在各区间内(45°间隔)相差在0.24%～2.81%之间,方差分析结果表明枝条水平分布与林木大小无关;不同大小林木的分枝角度有所差别,Ⅰ级木、Ⅲ级木和Ⅴ级木的平均分枝角度分别为48.5°、42.2°和50.7°。     

Identification of butterfly based on their shapes when viewed from different angles using an artificial neural network

Identification of butterfly species is essential because they are directly associated with crop plants used for human and animal consumption. However, the widely used reliable methods for butterfly identification are not efficient due to complicated butterfly shapes. We previously developed a novel shape recognition method that uses branch length similarity (BLS) entropy, which is a simple branching network consisting of a single node and branches. The method has been successfully applied to recognize battle tanks and characterize human faces with different emotions. In the present study, we used the BLS entropy profile (an assemble of BLS entropies) as an input feature in a feed-forward back-propagation artificial neural network to identify butterfly species according to their shapes when viewed from different angles (for vertically adjustable angle, θ = ± 10°, ± 20°, …, ± 60° and for horizontally adjustable angle, φ = ± 10°, ± 20°, …, ± 60°). In the field, butterfly images are generally captured obliquely by camera due to butterfly alignment and viewer positioning, which generates various shapes for a given specimen. To generate different shapes of a butterfly when viewed from different angles, we projected the shapes captured from top-view to a plane rotated through angles θ and φ. Projected shapes with differing θ and φ values were used as training data for the neural network and other shapes were used as test data. Experimental results showed that our method successfully identified various butterfly shapes. In addition, we briefly discuss extension of the method to identify more complicated images of different butterfly species.     

冀北山地阴坡优势树种的树体分维结构

以冀北山地阴坡两种混交林分中5种优势树种为研究对象,采用分形几何理论,论述了不同树种的树冠和侧枝分维结构,结果表明:(1)华北落叶松的树冠最宽处处于中上部(相对冠高的60％ -80％),白桦处于中部(40％-60％),山杨和糠椴都处于中下部(40％-50％),落叶松桦木混交林中的黑桦处于上部(70％ -80％),而山杨桦木混交林中黑桦则处于中部(50％-60％);(2)通过计盒维数法所得华北落叶松树冠的分形维数最大为1.690,山杨桦木混交林中4种树木分维数较接近(0.770-1.202),而两混交林中,前者白桦分维数(0.997)与后者(1.149)相似,而前者黑桦分维数(1.257)＞后者(0.770);(3)胸径13.1cm的华北落叶松侧枝在各方向上符合均匀分布,总体也符合均匀分布,前者中的黑桦在胸径15.8 cm时绝大多数方向上为均匀分布,前者中白桦及后者中4种树木在不同胸径时在各个方向上均为不均匀分布;(4)华北落叶松侧枝倾角随树龄增大分布在85-95°,糠椴则分布在55-85°.山杨树龄小(5.3)与树龄大(16.5)时分布在40-55°,中间树龄(10.5)分布在60-80°,黑桦分布在30-65°,前者中白桦倾角范围25-90°,后者则主要分布在45--85°;(5)采用网格覆盖法所得华北落叶松枝条的分维数平均值最高为1.772,其次为山杨桦木混交林中的4种树木,而两混交林中黑桦枝条的平均分维数却相差很大,其中前者为1.476,而后者为1.674.尽管同一树种侧枝形状大小各异,但相互间差异不显著,相关系数均在0.93以上,刻画了各枝条分枝格局的自相似共性.     

Directional selection by termites at a branching node created by a ballpoint pen

Subterranean termites excavate complex underground tunnels for foraging. Most tunnels comprise primary and secondary tunnels. Tunnels originating from the nest are called primary and those branching from the primary tunnels are named secondary tunnels; tertiary and quaternary tunnels are rarely observed. During foraging, termites may thus encounter a considerable number of tunnel-branching nodes. Directional selection at such a node is likely correlated to tunnel-growth activity because tunnels containing more termites have a higher probability of growth. In this study, we investigated how termites select the direction of movement at an artificially-designed branching node, by making chemical trails on filter paper, drawing lines using a ballpoint pen which contained the chemical substance that induces the termite to follow trails. The trails consisted of two lines: straight and branching. The branching line was drawn from the center of the straight line at an angle θ (10°, 20°,…, 90°). We then calculated the ratio of the directional selection as r = N_s/N_b, where N_s and N_b represent the number of straight and branching tunnels selected, respectively. The values of r were statistically classified into three groups based on the angle of the branching trail, as follows: 10° ≤ θ ≤ 20°, 30° ≤ θ ≤ 60°, and 70° ≤ θ ≤ 90°. Our paper briefly discusses the underlying mechanisms of the experimental results.     

Angles of nucleotides bound to cross-bridges in glycerinated muscle fiber at various concentrations of ϵ-ATP, ϵ-ADP and ϵ-AMPPNP detected by polarized fluorescence

The polarized fluorescence from nucleotides bound to myosin heads in glycerinated muscle fibers of rabbit psoas was measured as the number of myosin heads with bound nucleotides was varied by adding various concentrations of fluorescent ?-ATP, ?-ADP and ?-AMPPNP (1:N⁶-etheno-ATP, -ADP and -imido ATP). The angles of the absorption and emission dipoles of bound nucleotides to the fiber axis and their angular distribution were determined from the observed values of four components of the polarized fluorescence.The maximum amount of nucleotides bound to the myosin heads in the fiber, B_m, was 170 to 270 μm. The dissociation constant of nucleotides, $\text{K}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$, increased in the order ?-ATP, ?-ADP, ?-AMPPNP, and was four to six times larger at a sarcomere length (SL) of 2.1 μm than at 3.7 μm.The polarized fluorescence from bound ?-ADP at SL = 2.1 μm was independent of the amount of bound ?-ADP when it was lower than one-half of B_m, indicating a single helical array of myosin heads having ?-ADP. The angles of the absorption dipole, φ_A, and the emission dipole, φ_E, to the fiber axis were 69 ° and 66 °, respectively. As the amount of bound ?-ADP exceeded one-half of B_m, the values of the polarized fluorescence showed that the extra ?-ADP bound to myosin heads with a lower affinity and had different angles to the fiber axis: φ_A and φ_E were 49 ° and 54 °, respectively. The half-maximum width of the angular distribution of these bound ?-ADP molecules, $\text{θ}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$, was about 20 °.During development of isometric tension in the presence of ?-ATP with Mg²⁺, the polarized fluorescence was independent of the amount of bound ?-ATP when it was lower than one-third of B_m or when the concentration of free ?-ATP was lower than 100 μm, indicating a single helical array of myosin heads undergoing the ATPase reaction. The angles of bound nucleotides, φ_A and φ_E, were 68 ° and 64 °, respectively. The half-maximum width of the angular distribution, $\text{θ}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$, was about 22 °. As the amount of bound nucleotides exceeded one-third of B_m, the polarized fluorescence showed deviation from the values expected for the single helical array.The angles φ_A and φ_E for bound ?-AMPPNP were about 58 ° and 62 °, respectively, but the angular distribution was broad; that is, $\text{θ}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ was about 42 °. These angles were independent of the amount of bound ?-AMPPNP.In a stretched fiber with SL = 3.7 μm, the polarized fluorescence showed that the angles of ?-ADP, ?-ATP and ?-AMPPNP bound to myosin heads had almost random distributions; $\text{θ}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ was 90 ° to 100 °, independent of the amount of bound nucleotides. Similar results were obtained with the relaxed fiber in the presence of ?-ATP.     

Branch bending affected floral bud development and nutrient accumulation in shoot terminals of ‘Fuji’ and ‘Gala’ apples

Branch bending has been practiced for decades in China to induce flower buds in ‘Fuji’ apple. However, the optimum bending angle is yet to be elucidated. The main objectives of this study were to compare the effect of branch bending angles (70°, 90° and 110°) on the flowering and nutrient accumulation of 1-year-old shoots of ‘Fuji’ and ‘Gala’ apples and to determine the optimum branch bending angle for each cultivar. In both cultivars, the production of spurs and terminal flower buds, and the total sugar concentration and the carbon-to-nitrogen (C/N) ratio in the shoot terminals increased, whereas the N concentration decreased with increasing bending angles. The nutrient concentration was significantly higher in spurs than in medium and long shoots. The distinction between the changing patterns of C and N concentrations in the bent shoots during the growing season in our study suggested the competition of these two nutrients caused by vegetative and reproductive growth at different growing times. In ‘Fuji’ apple, the proportion of flowering buds appeared to increase more rapidly with the increase of bending angle from 70° to 110° than that in ‘Gala’ apple, and particularly a higher proportion of spurs was observed on ‘Fuji’ branches bent at a larger angle. The increase in the total sugar concentration and the C/N ratio in the shoot terminals of the bent branches might be involved in inducing floral buds after bending. The optimum bending angle was about 90° for ‘Gala’ apple and 110° for ‘Fuji’ apple, respectively. Bending could help farmers to reduce the severity of biennial fruiting in ‘Fuji’ apple.     

Phragmites australis at an extreme altitude: Rhizome architecture and its modelling

In central EuropePhragmites australis is a lowland plant, occurring rarely up to the tree line. In the Velká Kotlina cirque (Jeseníky mountains, NE Czech Republic), where it reaches its maximum altitude at about 1350 m a.s.l., its culms are 0.5–0.7 m high and the plants flower only in some years. During the last decade no germinable seeds have been observed. The architecture ofPhragmites rhizomes from this site was studied on seven randomly selected clonal fragments. They consisted of 3 to 10 partial tussocks (clumps) and 4 to 17 green shoots. The total length of the rhizomes was 9.7 to 50 m per plant. The number of nodes per plant was 96 to 431 and the longest internodes were 83 mm long. The number of side branches was 31 to 105 per plant. The branching angle depended on the type of branched rhizome. The mean angles of horizontal rhizomes, which connect individual tussocks, were relatively wide (modus 45°, arithmetic mean 37°), whereas within a tussock much sharper angles of branching prevailed (modal value 5°, arithmetic mean 15°). The mean internode-to-internode angle on continuing rhizomes was about 8°, with a wide variation. An architectural, spatially-explicit model ofPhragmites rhizome growth has been developed, showing that thePhragmites population in the studied locality can be maintained by vegetative multiplication, and seedling recruitment is not needed for its long-term persistence.     

The effect of using different coordinate systems on in-vivo hip angles can be estimated from computed tomography images

Measurements of hip kinematics inherently depend on the coordinate system in which they are derived, yet the effect of the coordinate system definition on calculations of hip angles is not well-understood. Herein, hip angles calculated during dynamic activities were compared using coordinate systems described in the literature. In-vivo kinematic data of 24 participants (13 males) were analyzed during gait and the anterior impingement test using dual fluoroscopy and model-based tracking. Two coordinate systems for the pelvis (anterior pelvic plane, International Society of Biomechanics [ISB]) and three coordinate systems for the femur (table top plane with two definitions of the superior-inferior axis, ISB) were evaluated. Bony landmarks visible on computed tomography (CT) images were identified to establish each coordinate system and used as the basis to calculate differences in hip angles between coordinate system pairs. In the analysis during gait, the maximum differences derived from various coordinate system definitions were 6.7° ± 5.5° for flexion, 7.7° ± 2.1° for rotation, and 5.5° ± 0.7° for adduction. For the anterior impingement test, the differences were 8.1° ± 5.9°, 7.1° ± 1.2°, and 5.3° ± 0.7°, respectively. Landmark-based analysis using CT images could estimate these dynamic differences with errors less than 1.0°. Our results indicate that hip angles can be accurately transformed to angles calculated in different coordinate systems by accounting for the inherent bony anatomy. This information may aid in the interpretation of results across biomechanical studies of the hip.     

A taxonomic revision of a Hypnea charoides-valentiae complex (Rhodophyta, Gigartinales) in Japan, with a description of Hypnea flexicaulis sp. nov.

Morphology of a Hypnea charoides‐valentiae complex (Rhodophyta, Gigartinales) in Japan is investigated on the basis of field‐collected and cultured plants. We can recognize two species, Hypnea charoides Lamouroux and H. flexicaulis Yamagishi et Masuda, sp. nov., which are distinguished by: (i) conspicuous percurrent main axes growing straight in the former versus less conspicuous percurrent main axes growing flexuosely in the latter; (ii) narrow branching angles (less than 90°) in the former versus wide branching angles (up to 150°) in the latter; (iii) the presence of branches and branchlets showing abrupt adaxial bending in the former versus those showing pronounced abaxial bending, some growing into hooked branchlets in the latter; and (iv) the absence (in the former) or presence (in the latter) of antler‐like branches. Nucleotide sequences of the plastid‐encoded large subunit of the ribulose‐1,5‐bisphosphate carboxylase/oxygenase gene (rbcL) support the differentiation of these two entities: the pairwise distance between them was 83 b.p. (6.2%).     

Polarized fluorescence from epsilon-ADP incorporated into F-actin in a myosin-free single fiber: conformation of F-actin and changes induced in it by heavy meromyosin.

Fluorescent ADP analog, ε-ADP (1:N⁶-ethenoadenosine 5′-diphosphate), was incorporated into F-actin in a myosin-free ghost single fiber and polarized fluorescence measurements were performed under a microspectrophotometer to investigate the conformation of F-actin and the changes induced in it by heavy meromyosin and subfragment-1. Four components of polarized fluorescence were obtained by exciting the fiber with light polarized parallel and perpendicular to the long axis of the fiber and measuring the intensity of emission polarized parallel and perpendicular. From these data it was shown that F-actin in the fiber was not rigid but flexible, with a value for the elastic modulus for bending of 5.3 × 10^?17 dyn cm². The angles of absorption dipole and emission dipole of bound ε-ADP with the long axis of F-actin were both about 75 °.The binding of heavy meromyosin decreased the elastic modulus of F-actin by 30% and the angles of absorption and emission dipoles by 2.5 ° and 1.5 °, respectively. The molar ratios of bound heavy meromyosin and subfragment-1 to actin in the ghost fiber at saturation were 0.3 and 0.6, respectively, being smaller than those in solution.     

Tree Branching: Leonardo da Vinci's Rule versus Biomechanical Models

This study examined Leonardo da Vinci''s rule (i.e., the sum of the cross-sectional area of all tree branches above a branching point at any height is equal to the cross-sectional area of the trunk or the branch immediately below the branching point) using simulations based on two biomechanical models: the uniform stress and elastic similarity models. Model calculations of the daughter/mother ratio (i.e., the ratio of the total cross-sectional area of the daughter branches to the cross-sectional area of the mother branch at the branching point) showed that both biomechanical models agreed with da Vinci''s rule when the branching angles of daughter branches and the weights of lateral daughter branches were small; however, the models deviated from da Vinci''s rule as the weights and/or the branching angles of lateral daughter branches increased. The calculated values of the two models were largely similar but differed in some ways. Field measurements of Fagus crenata and Abies homolepis also fit this trend, wherein models deviated from da Vinci''s rule with increasing relative weights of lateral daughter branches. However, this deviation was small for a branching pattern in nature, where empirical measurements were taken under realistic measurement conditions; thus, da Vinci''s rule did not critically contradict the biomechanical models in the case of real branching patterns, though the model calculations described the contradiction between da Vinci''s rule and the biomechanical models. The field data for Fagus crenata fit the uniform stress model best, indicating that stress uniformity is the key constraint of branch morphology in Fagus crenata rather than elastic similarity or da Vinci''s rule. On the other hand, mechanical constraints are not necessarily significant in the morphology of Abies homolepis branches, depending on the number of daughter branches. Rather, these branches were often in agreement with da Vinci''s rule.     

Changes in human skeletal muscle architecture and function induced by extended spaceflight

The aim of this study was to quantitatively describe the relationships between joint angles and muscle architecture (lengths (L_f) and angles (Θ_f) of fascicles) of human triceps surae [medial (MG) and lateral (LG) gastrocnemius and soleus (SOL) muscles] in vivo for three men-cosmonaut after long-duration spaceflight. Sagittal sonographs of MG, LG, SOL were taken at ankle was positioned at 15° (dorsiflexion), 0° (neutral position), +15°, and +30° (plantarflexion), with the knee at 90° at rest and after a long-duration spaceflight. At each position, longitudinal ultrasonic images of the MG and LG and SOL were obtained while the cosmonauts was relaxed from which fascicle lengths and angles with respect to the aponeuroses were determined. After space flight plantarflexor force declined significantly (26%; p < 0.001). The internal architecture of the GM, and LG, and SOL muscle was significantly altered. In the passive condition, L_f changed from 45, 53, and 39 mm (knee, 0°, ankle, −15°) to 26, 33, and 28 mm (knee, 90° ankle, 30°) for MG, LG, and SOL, respectively. Different lengths and angles of fascicles, and their changes by contraction, might be related to differences in force-producing capabilities of the muscles and elastic characteristics of tendons and aponeuroses. The three heads of the triceps surae muscle substantially differ in architecture, which probably reflects their functional roles. Differences in fiber length and pennation angle that were observed among the muscles and could be associated with differences in force production and in elastic properties of musculo-tendinous complex and aponeuroses.     

大棕蝠下丘听神经元频率调谐的方向敏感性

实验在8只大棕蝠(Eptesicusfuscus)上进行.选取了5个声源方位记录部位对侧80°(C-80°)、40°(C-40°)、0°和同侧40°(I-40°)、80°(I-80°).下丘听神经元的频率调谐曲线的形状有三种V型、封闭型和U型.以C-40°的频率调谐曲线为对照,声源方位改变时,多数神经元频率调谐曲线的形状和最佳频率不变.多数神经元在声源方位由记录部位对侧转向同侧时,频率调谐曲线的锐度(以QndB值为指标)由小变大;神经元在I-80°、I-40°的QndB值显著高于C-80°、C-40°、0°的QndB值.在所观察的47个神经元中,5个声源方位的最低阈值的平均值有显著差异,由高到低的分布为MTI-80°＞MTI-40°＞MT0°＞MTc-80°＞MTc-40°.我们推测,声源方位对神经元频率调谐特性影响的机制,可能是抑制性和兴奋性输入的比例不同而相互整合的结果.     

Comparative structural studies of the first row early transition metal(III) chloride tetrahydrofuran solvates

Two compounds of empirical formula MCl₃- (THF)₃, M = V and Cr, have been characterized by single crystal X-ray studies. The VCl₃(THF)₃ molecule, which has a mer octahedral stereochemistry, crystallizes in the monoclinic space group P2₁/c with a= 8.847(2),b= 12.861(5),c= 15.134(3) Å, β = 91.94(2)°, V = 1721(1) ų and Z = 4. The V-Ci(1) and V-CI(2) distances have a mean value of 2.330 [3] Å while V-CI(3) = 2.297(2) Å, The VO(1) and VO(2) distances have a mean value of 2.061[8] Å while V-O(3) = 2.102(3) Å cis ClVCl angles average 92.0[5]° and cis OVO angles average 86.2[2]° . The isostmctural complex, CrCl₃(THF)₃, has a crystal structure made up of discrete octahedral mer-CrCl₃(THF)₃ molecules with the following unit cell dimensions (space group P2₁/c): a = 8.715(1), b= 12.786(3), c = 15.122(3) Å, β = 92.15(1)°, V = 1684(1) ų and Z = 4. The CrCl(1) and CrCl(2) distances have a mean value of 2.310131 Å while CrCl(3) = 2.283(2) Å. The CrO(1) and CrO(2) distances have a mean value of 2.0101171 Å while CrO(3) = 2.077(4) Å. cis ClCrCl angles average 90.9[4]° and cis OCrO angles average 86.1 [2]°. The structures of these two octahedral complexes and those previously reported for ScCl₃(THF)₃ and TiCl₃(THF)₃ are compared and certain general trends are discussed.     

Gravity can induce epinastic bending of isolated leaves

Abstract Isolated leaves of Plectranthus fruticosus were grown in cubic plastic cuvettes, and were supplied via their cut petioles with nutrient solution and indole-3-acetic acid (10^?6m ). Holes bored in the cuvette walls allowed the petioles to be oriented at approximately 60°, 90° or 120° to the vertical. Growth of the leaves initially oriented at angles of 60° and 90°, which simulated the situation in the intact plant, did not result in epinastic bending of the petiole. Inversion of the leaves (adaxial surface of the petiole downwards) and orientation of the adaxial/abaxial surfaces of the horizontal petiole parallel to the gravity vector, however, yielded strong epinastic bending of the petioles. In the latter case, this bending was not in the direction of the gravity vector (evidence for point (iii), below). Furthermore, epinastic bending occurred, when the isolated leaves were rotated on a clinostat (petioles parallel to the rotation axis or inclined to the rotation axis at an angle of 30°; 3 r.p.m.). Since a possible influence of the shoot was excluded, it is concluded that (i) perception and response are restricted to the leaf, (ii) gravity alone is sufficient to induce epinasty, (iii) a gravitropic component of the response can probably be excluded. The clinostat induced epinasty may not have been caused by nullifying the effect of gravity but due to continuous gravistimulation of the leaf.     

Gravitropism of Primary Roots of Zea mays L. at Different Displacement Angles

Primary roots of Zea mays were oriented at various angles fromthe vertical ranging from 99° to 1° and their subsequentbending analysed from filmed records. The maximum rate of bendingand the time before bending commenced both varied two-fold,but showed no correlation with the initial angle of tip displacement.Roots orientated to small initial angles (< 40°) oftenovershot the vertical and proceeded to oscillate around thisorientation, whereas roots oriented to large initial angles(> 60°) often failed to achieve the vertical. Roots inthis latter group resumed bending after an indeterminate time,or did so immediately after a second displacement of their tip,showing that they were not intrinsically unable to bend. Theapparently spontaneous resumption of bending after a temporaryplagiogravitropic phase is suggested as being due to noise inthe graviperception system in the root cap. The tips of rootsgrowing vertically downwards showed oscillatory bending movementsup to 10° either side of vertical. This angle correspondsto the minimum angle of displacement which induces gravitropicbending. Only when roots were oriented 10-20° from verticaldid they begin unequivocally to show a gravitropism since atsuch angles the deflection of their tips exceeded that due totheir natural oscillation.Copyright 1993, 1999 Academic Press Gravitropism, roots, Zea mays     

Solution Structure of a Parallel Left-handed Double-helical Gramicidin-A Determined by 2D1H NMR

The structure of a parallel left-handed double-helical form of gramicidin was detected by circular dichroism spectroscopy and determined using 500 and 600 MHz NMR in CaCl₂/methanol solution. Measurements of TOCSY, DQF-COSY and NOESY spectra were converted into 604 distance and 48 torsional angle constraints for structure calculations. Stereospecific assignments and χ₁angles were calculated using³J_αβ, d_αβ(i,i), d_Nβ(i,i) and d_Nγ(i,i). χ₂angles were determined using d_αβ(i,i), d_Nβ(i,i), d_βδ(i,i), d_Nγ(i,i) and d_αγ(i,i). The calculations of initial structures were performed using the distance geometry/simulated annealing method in XPLOR. The initial structures were further refined and energy minimized using simulated annealing/molecular dynamics methods. Back-calculations for every generated structure were also performed to check their consistency with the experimental data.187 final structures with no violations above the threshold conditions (0.05 Å, 5°, 5°, 0.5 Å and 5° for bonds, angles, improper, NOE and cdihe, respectively) were produced from the 200 initial structures. Twenty structures with the lowest NOE energies were used for further analysis. The average r.m.s. deviations for the 20 structures are 0.64 Å for backbone and 1.1 Å for all non-hydrogen atoms.Gramicidin in this form, with approximately 5.7 residues per turn, is a parallel double helical dimer. The length along the helix axis is about 30 Å and the inner pore diameter varies from 1 to 2 Å. It is different from all other gramicidin structures determined to date. The presence of Ca^{2 +}stabilises a conformation that prevents the binding of monovalent cations. It is likely that this structure is related to a non-channel, antibiotic role of gramicidin.     

The induction of oxidative stress in cervix carcinoma cells by levoglucosenone derived 4-S-salicyl derivative and (1–4)-S-thio-disaccharides. Part 4

(1–4)-S-thiodisaccharides were shown to kill various cancer cell lines, including cervix, lung, mammary-gland and colon by unknown mechanisms. Here we identified two actions of levoglucosenone derived (1–4)-S-thiodisaccharides against cervix cancer cells: induction of oxidative stress and DNA damage. In consequence, (1–4)-S-thiodisaccharides lowered the cellular GSH level and changed the expression profile of genes encoding key proteins involved with oxidative stress response. We also observed that (1–4)-S-thiodisaccharides induced DNA damage and interfered with the thioredoxin (Trx) system. Both actions, as induced by FPC6, were stronger when dihedral angles of sulfur bridge were set to 110°, 100° and 109°, clearly indicating differences when compared to FPC8. These findings demonstrate that the 1–4-thio bridge of disaccharide is a powerful anticancer pharmacophore, and its potential use needs further studies.     

Ribosome structure: hand determination by electron microscopy of 30 S subunits.

Negatively stained Escherichia coli 30 S ribosome subunits have been examined by electron microscopy at tilt angles of ?45 °, 0 ° and +45 °. The tilted views, together with images of metal shadowed particles are consistent with an asymmetric model for the structure of the 30 S subunit and enable the absolute hand of the particle to be determined.