bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis of Functionalized Rab GTPases by a Combination of Solution‐ or Solid‐Phase Lipopeptide Synthesis with Expressed Protein Ligation
Authors: Brunsveld Luc , Watzke Anja , Durek Thomas , Alexandrov Kirill , Goody Roger S. , Waldmann Herbert 
Published: February 2005

AbstractPrenylated proteins with non‐native functionalities are generally very difficult to obtain by recombinant or enzymatic means. The semisynthesis of preparative amounts of prenylated Rab guanosine triphosphatases (GTPases) from recombinant proteins and synthetic prenylated peptides depends largely on the availability of functionalised prenylated peptides corresponding to the proteins' native structure or modifications thereof. Here, we describe and compare solution‐phase and solid‐phase strategies for the generation of peptides corresponding to the prenylated C terminus of Rab7 GTPase. The solid‐phase with utilisation of a hydrazide linker emerges as the more favourable approach. It allows a fast and practical synthesis of pure peptides and gives a high degree of flexibility in their modification. To facilitate the analysis of semisynthetic proteins, the synthesised peptides were equipped with a fluorescent group. Using the described approach, we introduced fluorophores at several different positions of the Rab7 C terminus. The position of the incorporated fluorescent groups in the peptides did not influence the protein‐ligation reaction, as the generated peptides could be ligated onto thioester‐tagged Rab7. However, it was found that the positioning of the fluorescent group had an influence on the functionality of the Rab7 proteins; analysis of the interaction of the semisynthetic Rab7 proteins with REP (Rab escort protein) and GDI (guanosine diphosphate dissociation inhibitor) molecules revealed that modification of the peptide side chains or of the C‐terminal isoprenoid did not significantly interfere with complex formation. However, functionalisation of the C terminus was found to have an adverse effect on complex formation and stability, possibly reflecting low structural flexibility of the Rab GDI/REP molecules in the vicinity of the lipid‐binding site.
Water‐Insoluble Ag–U–Organic Assemblies with Photocatalytic Activity
Authors: Yu Zhen‐Tao , Liao Zuo‐Lei , Jiang Yu‐Sheng , Li Guang‐Hua , Chen Jie‐Sheng 
Published: February 2005

AbstractTwo metal–organic coordination polymers [Ag(bipy)(UO2)(bdc)1.5] (bipy=2,2′‐bipyridyl, bdc=1,4‐benzenedicarboxylate) and [Ag2(phen)2UO2(btec)] (phen=1,10‐phenanthroline, btec=1,2,4,5‐benzenetetracarboxylate) were obtained by hydrothermal assembly of the d10 metal silver and the 5f metal uranium with mixed ligands. Both compounds form two‐dimensional networks with π–π overlap interactions between the aromatic fragments in the neighboring layers. In aqueous suspension the two water‐insoluble materials show photocatalytic degradation performance superior to that of commercial TiO2 (Degussa P‐25) when tested on nonbiodegradable rhodamine B (RhB) as model pollutant. The relationship between the structure of the photocatalysts and the photocatalytic activity was also elucidated. On the basis of the monitored intermediate species and the final mineralized products, it is proposed that the possible reaction mechanism for the photodegradation (oxidation) of RhB in aqueous solution catalyzed by the two assembly compounds involves photoexcitation of uranyl centers and molecular oxygen.
Preparation of N‐(4‐Methylpentane‐2‐yl)‐N′‐ [2‐(2‐phenylpropane‐2‐yl)]‐benzene‐1,4‐diamine.
Authors: Sigmundova Ivica , Uhlar Jan , Toma Stefan 
Published: February 2005

AbstractFor Abstract see ChemInform Abstract in Full Text.
One‐Pot Synthesis of Helical Aromatics: Stereoselectivity, Stability Against Racemization, and Assignment of Absolute Configuration Assisted by Experimental and Theoretical Circular Dichroism.
Authors: Watanabe Masashi , Suzuki Hiroshi , Tanaka Yasutaka , Ishida Toshimasa , Oshikawa Tatsuo , Tori‐i Akiyoshi 
Published: February 2005

AbstractFor Abstract see ChemInform Abstract in Full Text.
Highly Efficient Synthesis of (R)‐ and (S)‐Piperazic Acids Using Proline‐Catalyzed Asymmetric α‐Hydrazination.
Authors: Henmi Yoshiaki , Makino Kazuishi , Yoshitomi Yayoi , Hara Osamu , Hamada Yasumasa 
Published: February 2005

AbstractFor Abstract see ChemInform Abstract in Full Text.
Agariblazeispirol C (I) from the Cultured Mycelia of the Fungus, Agaricus blazei, and the Chemical Conversion of Blazeispirol A.
Authors: Hirotani Masao , Masuda Miyuki , Sukemori Aya , Hirotani Seiko , Sato Noriko , Yoshikawa Takafumi 
Published: February 2005

AbstractFor Abstract see ChemInform Abstract in Full Text.
Synthesis of 1,6‐Anhydro‐2,3,4‐trideoxy‐2,3‐epimino‐ and 1,6‐Anhydro‐2,3,4‐trideoxy‐3,4‐epimino‐β‐D‐hexopyranoses and Their NMR and Infrared Spectra.
Authors: Karban Jindrich , Budesinsky Milos , Kroutil Jiri 
Published: February 2005

AbstractFor Abstract see ChemInform Abstract in Full Text.
Role of Platelet Derived Endothelial Cell Growth Factor/Thymidine Phosphorylase in Fluoropyrimidine Sensitivity and Potential Role of Deoxyribose‐1‐phosphate
Authors: de Bruin M. , van Capel T. , Smid K. , van der Born K. , Fukushima M. , Hoekman K. , Pinedo H. M. , Peters G. J. 
Published: February 2005

AbstractFor Abstract see ChemInform Abstract in Full Text.
8‐Substituted‐9‐deazaxanthines as Adenosine Receptor Ligands: Design, Synthesis and Structure‐Affinity Relationships at A2B.
Authors: Carotti Angelo , Stefanachi Angela , Ravina Enrique , Sotelo Eddy , Loza Maria Isabel , Cadavid Maria Isabel , Centeno Nuria B. , Nicolotti Orazio 
Published: February 2005

AbstractFor Abstract see ChemInform Abstract in Full Text.
Tubulin nucleation and assembly in mitotic cells: Evidence for nucleic acids in kinetochores and centrosomes
Authors: Pepper Daniel A. , Brinkley B. R. 
Published: February 2005

AbstractA lysed cell system was used to study the organelle structure and nucleation of exogenous tubulin at kinetochores and centrosomes in mitotic PtK2 cells. We have used this lysed cell system in conjunction with nuclease digestion experiments to determine which specific nucleic acids (DNA or RNA) are involved in either the structure and/or microtubule‐initiating capacity of kinetochores and centrosomes. The results indicate that DNase I specifically decondenses the kinetochore plate structure, with the eventual loss in the ability of the chromosomes to nucleate microtubule assembly. DNase I had no effect on either the structure or nucleating capacity of centrosomes. Both RNase T1 and RNase A specifically attacked the amorphous pericentriolar material of the centrosomes, with a concomitant loss in the ability of this material to nucleate microtubule formation. Neither RNase appeared to affect the structure or nucleating capacity of the kinetochore. Therefore, the two types of nucleases appear to exert preferential effects on the different types of microtubule initiation sites in mitotic mammalian cells. The results suggest that DNA is a major component of the kinetochore, while RNA is a major component of the amorphous pericentriolar material. These findings support the concept that microtubule initiation sites in mitotic cells contain nucleic acids which are essential for the structural and functional integrity of the sites.
Redistribution of actin and fascin in sea urchin eggs after fertilization
Authors: Otto J. J. , Kane R. E. , Bryan J. 
Published: February 2005

AbstractFollowing fertilization, the sea urchin egg cortex undergoes a structural change involving the assembly and organization of actin filaments into microvilli. Antifascin localizes this actin cross‐linking protein in the microvilli of the fertilized egg cortex but no organized staining is present in the unfertilized cortex. Determination of the actin content of eggs using the DNAase I inhibition assay indicates that actin is about 1.4% of the total protein. Approximately 90% of this actin is soluble in low calcium isotonic extracts of unfertilized eggs while only 60–65% can be recovered in identical extracts of fertilized eggs. Similar measurements for fascin using a radioimmunoassay indicate this molecule represents about 0.3% of the total egg protein, essentially all of which is recovered in low calcium isotonic extracts of unfertilized eggs. After fertilization only 65–70% of this actin cross‐linking protein is in the soluble phase. These results demonstrate a markedly different solubility for actin and fascin after fertilization, when the indirect immunofluorescence staining localizes fascin in the microvilli, and are consistent with the idea that fascin organizes newly polymerized actin filaments into the microvillar cores. A consideration of the amounts of actin and fascin incorporated into the cortex after fertilization and the number of microvilli on the egg surface indicates that the measured values are sufficient to account for the observed microvillar elongation.
Physarum myosin light chain binds calcium
Authors: Kessler D. , Eisenlohr L. C. , Lathwell M. J. , Huang J. , Taylor H. C. , Godfrey S. D. , Spady M. L. 
Published: February 2005

AbstractMyosin from the slime mold Physarum polycephalum contains three sizes of polypeptides: a heavy chain and two light chains, LC‐1 and LC‐2. Using a simple qualitative test for calcium binding by comparing electrophoretic migration of the polypeptides in sodium dodecy1 sulfate (SDS) acrylamide gels in the presence and absence of calcium, we have found that Physarum myosin light chain LC‐2 migrates with an apparent molecular weight of 16,900 daltons in the presence of the metal ion chelator ethylene glycol bis (B‐aminoethyl ether) N,N′‐tetraacetic acid (EGTA). However, if calcium chloride is added to the sample prior to electrophoresis, the apparent molecular weight decreases to 16,100. Lanthanide and cadmium ions, but not magnesium, can substitute for calcium. Because the ionic radii of Ca2+, La3+, and Cd2+ are almost identical, we conclude that Physarum myosin LC‐2 possesses a very size‐specific binding site for calcium. Physarum myosin LC‐1 and the heavy chain give no evidence for binding calcium by this test. Since cytoplasmic streaming in the plasmodium of Physarum requires calcium, our evidence indicates that the calcium‐binding property of Physarum myosin LC‐2 may be important in regulating the production of force by actomyosin in the ectoplasm. Unexpectedly, the myosin light chain in Physarum capable of binding calcium, LC‐2, is the essential light chain, while LC‐1 is a member of the regulatory class of myosin light chains [V. T. Nachmias, personal communication]. Until now, essential myosin light chains have not been shown to have high affinity divalent cation binding sites. This means a new version of the myosin‐based model for actomyosin regulation by calcium may be required to explain cytoplasmic movement in Physarum, and perhaps in other motile systems involving cytoplasmic myosins as well.
Motion of polymorphonuclear leukocytes: Theory of receptor redistribution and the frictional force on a moving cell
Authors: Dembo Micah , Tuckerman Laurette , Goad Walter 
Published: February 2005

AbstractAs a cell moves over a surface, the distribution of membrane proteins that adhere to the surface will be changed relative to the distribution of these molecules on a static cell. Observations of this redistribution offer, in principle, evidence as to the mechanisms of membrane dynamics during cell locomotion. Toward extracting such information we present and analyze a mathematical model of receptor transport in the membrane by diffusion and convection, as affected by the making and breaking of the bonds between the receptors and the surface as the cell moves.We show that the disruption of receptor‐surface bonds at the tail of the cell provides a mechanism by which the frictional force opposing a cell's motion is exerted, and calculate the magnitude of this force as a function of cell velocity. Assuming this to be the major contribution to the frictional force, we show that when the shear force on a cell is above a critical value it is no longer possible for the cell to slide across the surface. For such large forces, it is still possible for the cell to roll; alternatively the cell can be torn free of the surface.Our analysis of existing data on movement of polymorphonuclear leukocytes indicates that cell motion is not accompanied by a bulk flow of membrane from the front to the back of the cell. The data also indicate that cells do not tend to roll as they move over a surface under normal conditions. The data are most consistent with a model where the membrane as a whole is stationary but where receptors that bind to the surface become coupled to sub‐membrane contractile proteins.
Video‐enhanced contrast, differential interference contrast (AVEC‐DIC) microscopy: A new method capable of analyzing microtubule‐related motility in the reticulopodial network of allogromia laticollaris
Authors: Allen Robert Day , Allen Nina Strömgren , Travis Jeffrey L. 
Published: February 2005

AbstractA new method called Allen Video‐enhanced Contrast, Differential Interference Contrast (AVEC‐DIC) microscopy is shown to be sufficiently sensitive to detect several new features of microtubule‐related motility in the reticulopodial network of the foraminifer, Allogromia. The method takes advantage of the variable gain and offset features of a binary video camera to operate the DIC microscope under conditions highly favorable for video imaging, but in which the optical image is virtually invisible to the eye yet retains its full information when viewed by a suitable video camera. The improvements are made possible by setting a dé Senarmont compensator to λ/9‐λ/4 at maximal working aperture of internally corrected planapochromatic objectives. Under these conditions, the offset feature of the video camera can reject so much stray light from the instrument and specimen that contrast compares favorably with that observed in high‐extinction images, and polarizing rectifiers offer scarcely any advantage. Freed from the constraints of the light‐limited conditions of DIC microscopy, video images can be recorded 60 times per second, or over 1,000 times the rate of photomicrographs at comparable magnifications under high‐extinction conditions.Application of this method to the reticulopodial network of Allogromia has shown that cytoplasmic organelles are translocated only in contact with single microtubules or bundles of microtubules, and that these organelles fail to move when separated from microtubules. Microtubules themselves undergo both axial translatory (“sliding”) and lateral “zipping and unzipping” movements that have been suggested to occur during mitosis and other biological processes.
The motion mechanics of Nitella filaments (Cytoplasmic streaming): Their imitation in detail by screw‐mechanical models
Authors: Foissner Iise , Jarosch Robert 
Published: February 2005

AbstractOur knowledge about the actin‐containing characean filaments on the basis of light and electron microscopical investigations is reviewed. Dynamic filamentous networks, known already from isolated droplets, were detected in Nitella rhizoidal cells using light microscopical techniques. Earlier light microscopic observations in cytoplasmic droplets are confirmed and complemented by new model experiments with rotating helices. The motile phenomena occurring at the filament bundles (ring formation, wave propagation, particle translocation, net dynamics, rolling motions, formation of side arms) can, in this way, be imitated in detail. Thus, the concept of cytoplasmic streaming as a translocation along bundles of rapidly rotating helical filaments is supported. In order to explain unidirectional cytoplasmic streaming, a periodic winding up and unwinding of fine filaments is postulated by which ions are periodically bound and displaced. The formation of side arms which is favored during unwinding results in a screw‐mechanical different behavior of the filaments in the two directions of rotation and therefore causes permanent particle transport in one direction.
Tropomyosin binding to F‐actin protects the F‐actin from disassembly by brain actin‐depolymerizing factor (ADF)
Authors: Bernstein Barbara W. , Bamburg James R. 
Published: February 2005

AbstractBrain or muscle F‐actin is rapidly depolymerized to monomeric actin in vitro by actin‐depolymerizing factor, a protein isolated from chick embryo brain. Binding of muscle tropomyosin to muscle F‐actin protects the F‐actin from depolymerization by this factor. A 8.4/1.0 molar ratio of actin subunits to tropomyosin, achieved by incubation of the F‐actin with excess tropomyosin, protects 58% of the F‐actin from depolymerization by excess actin‐depolymerizing factor for at least 3 hr at 25°C. Thus, actin‐depolymerizing factor seems to be specifically directed toward actin filaments lacking tropomyosin.
Pseudopod formation and membrane production during prey capture by a heliozoon (feeding by Actinophrys, II)
Authors: Hausmann Klaus , Patterson David J. 
Published: February 2005

AbstractTwo phases of prey capture by the heliozoon Actinophrys sol are documented by electron microscopy. The phases are those of prey adhesion to the predator and enclosure of the prey by the predator. Adherence is brought about by numerous small pieces of adhesive membrane produced by the predator at the site of prey contact. Some of the heliozoan extrusomes expel their contents at this time, but the significance of this event is unclear. Enclosure of the prey is effected by a funnelshaped pseudopodium. This is drawn over the prey by the action of the leading margin. The ultrastructural appearance of the cytoplasm of the leading margin differs from the rest of the cell, being homogeneous and finely filamentous. Both force and traction for the progression of the pseudopod are generated primarily at the tip. During the development of the funnel‐pseudopod, extrusomes expand and fuse with each other and with the plasma membrane. Their investing membrane is thereby made available as food vacuole membrane.
Epithelial cell motility: The effect of 2‐deoxyglucose on cell migration, atp production, and the structure of the cytoplasmic ground substance in lamellipodia of epithelial cells in culture
Authors: Gibbins J. R. 
Published: February 2005

AbstractUsing a line of epithelial cells (SCCA5) derived from a spontaneous rat carcinoma, the glucose analogue 2‐deoxyglucose (2DG) has been shown by time‐lapse cinemicrography to produce a cessation of motility by 1 hour that can be reversed by replacement of the 2DG, and does not occur in equivalent media with or without glucose or in 2DG‐containing media with added pyruvate and citrate. The effect on the cells at the edge of an epithelial island is to prevent the formation of new lamellipodia and produce a progressive retraction and condensation of lamellipodia already present. This effect of 2DG on motility corresponds with a significant reduction in the level of ATP that is partially restored after 30 minutes in the recovery incubation. Only a slight reduction in protein synthesis occurs in the presence of 2DG. The external morphology and the cytoplasmic ground substance of the cells were studied by scanning electron microscopy and high voltage electron microscopy respectively. It was found that after incubation in 2DG for 1 hour the outline of the free edges of the cells was distorted resulting in redistribution of microvilli, condensation of cytoplasm into strands, and irregular projections from the edges of residual lamellipodia. The structure of the cytoplasmic ground substance in lamellipodia from cells incubated in 2DG for 3 hours was distinctly different from that in cells incubated for 3 hours in 2DG then recovered for 25 minutes, or in cells incubated in glucose‐containing medium for 3 hours. In the 2DG‐treated cells the lattice‐like structure evident in critical‐point‐dried cells was condensed into short thick strands that terminated in bulbous ends, whereas in cells recovered for 25 minutes the lattice material was elongated and tapering and the interlattice space relatively expanded. The results obtained support the concept of modulation occuring in the structure of the microtrabecular lattice component of the cytoplasmic ground substance coincident with alterations in cell function and metabolic state.
Tomato actin and myosin: Contractile proteins from a higher land plant
Authors: Vahey Maryanne , Titus Margaret , Trautwein Richard , Scordilis Stylianos 
Published: February 2005

AbstractThis paper describes the initial isolation of actin‐ and myosin‐like proteins from the cytoplasm of the endocarp tissue cells of the fruit of the tomato, Lycopersicon esculentum. Low ionic strength buffers extracted the 42,000 molecular weight tomato actin in the depolymerized form. Tomato actin can be polymerized in 0.1 M KCl, 2 mM MgCl2 to form 6 nm diameter filaments resembling rabbit skeletal muscle F‐actin in their ultrastructure and pattern of decoration with rabbit myosin subfragment‐1 (S‐1). Tomato F‐actin activates the low ionic strength Mg2+ ATPase of rabbit S‐1 up to ten‐fold. High ionic strength extracts of tomato yield a myosinlike enzyme whose ATPase activity in 0.5 M KCl is maximal in the presence of K+‐EDTA and is repressed in the presence of Mg2+. The column‐purified enzyme forms a complex with rabbit F‐actin, which can be dissociated by Mg2+ ATP. The low ionic strength Mg2+ ATPase of tomato myosin can be activated ten‐fold by rabbit actin and up to nineteen‐fold by tomato actin. No activation of the tomato myosin by rabbit F‐actin occurs in the absence of free calcium ions.
Dynamic aspects of the supramolecular organization of intermediate filament networks in cultured epidermal cells
Authors: Jones Jonathan C. R. , Goldman Anne E. , Steinert Peter M. , Yuspa Stuart , Goldman Robert D. 
Published: February 2005

AbstractWe have shown, by indirect immunofluorescence microscopy using an antiserum against the mouse keratin subunit K2 and by electron microscopy, that transformed (PAM) and primary (PME) mouse epidermal cells possess extensive net works of IF bundles. Following trypsinization and replating of PAM cells, IF bundles are seen to move as a continuous net work from a perinuclear zone into the peripheral cytoplasmic regions. In PAM cells lysed in high‐ionic‐strength solutions containing Triton ×‐100 and DNAase‐1, IF bundles appear to be closely associated with nuclear envelope remnants and, in some cases, appear to be attached to nuclear pore complexes. PME cells cultivated in low Ca2+‐containing medium possess perinuclear birefringent arrays of IF bundles. Within 2 hours of switching the cells to normal Ca2+ levels, the PME IF bundle network moves towards and establishes contact with the cell surface as desmosomes form. Live cells observed by phase contrast and fixed cells observed by immunofluorescence microscopy demonstrate that desmosomes can be distinguished as dark bands separating neighboring cells. There is little difference between the major proteins seen in SDS‐polyacrylamide gel profiles of isolated IF bundle net works from PME cells before and after the Ca2+ switch. Therefore, a reorganization of relatively insoluble membrane‐associated protein following the Ca2+ switch may be involved in desmosome formation. The isolated IF networks from PAM cells differ in protein composition compared to the PME IF networks. This may be related to the greatly reduced number of desmosomes in PAM cells. The IF bundle system in epidermal cells appears to be involved in shape formation, shape maintenance, the establishment of desmosomes, nuclear centration, and cell‐cell contact.